Although the authors stated that the selection criterion for the operation was a good neurological status of the patient (unfortunately “good neurological status” was not defined precisely), data presented in Table 1 show that there were also people in the study group who were graded 13 points on the Glasgow Coma Scale (GCS) scale.

We have some doubts whether it was possible to explain the details of the operation to patients with such a low score and to ensure that the special requirements for the intraoperative interaction between the patient and the medical team were properly and reliably understood by the patient.

We have further doubts about selecting for ACs under CS patients with severe obesity, anticipated difficult airway, and severe respiratory (lung tumour compressing the aorta) and cardiovascular comorbidities.

In our opinion, such patients meet the criteria for a predicted anatomical and physiological difficult airway, and in the context of restricted access to the patient, emergency airway management would be extremely challenging.

The risk of severe complications related to airway management (including death and brain damage) was outlined in the excellent British NAP4 study, which showed the significance of proper identification of patients at risk of difficult airway and the need for advance planning to reduce the risk of a fatal outcome [2].


In Table 2, the authors indicate that they encountered four difficult intubations in 15% of operated patients but did not explain the reasons for instrumentation on the airways.

We also noticed that some patients were operated on in positions that could pose additional difficulties with access to the airways, if needed.

According to the information found in the article there was a group of patients who were operated on in a prone position.

Postoperative survey carried out in our centre revealed that one third of patients who were operated on in conscious sedation in a neutral or lateral position complained about discomfort.

We expect that staying in a prone position during lengthy (over 6 hours) procedures may be challenging for a conscious patient [3].


We strongly agree with the authors’ opinion that dexmedetomidine can be an excellent choice in AC surgery but have some concerns about the choice of less controllable midazolam and oxycodone as a supplement to sedation and analgesia.

We agree with the authors that further studies are needed to confirm the best and safest anaesthetic protocol for awake craniotomy.


Dear Editor, We are responding to the questions raised by our colleagues from Warsaw (commentary by Surówka et al.) [ 1] following the publication of our study “Awake craniotomy with dexmedetomidine during resection of brain tumours located in eloquent regions” [2].

We appreciate this discussion, as it could enhance the management of patients undergoing the awake craniotomy procedure.

The proper patient selection for awake craniotomy (AC) under conscious sedation (CS) is an important factor that influences possible adverse events during the procedure.

Therefore, in our study, a psychologist carefully evaluated each patient at least one day before the procedure to identify the risk factors of uncooperativeness, overwhelming stress, and an inability to understand and follow commands or answer questions.

Patients with significant intellectual or psychiatric disorders were disqualified from AC.

Some patients with somnolence, aphasia or motor impairment were recognised as candidates for AC under CS because they could cooperate and answer questions once aroused, which was confirmed by the psychologist.

In our study, we defined patients as having a “good neurological status” if they passed all psychological tests preoperatively.

Additionally, in our group, only one patient had a Glasgow Coma Scale (GCS) of 14 points, and the rest had a GCS of 15 points (Table 1 should show GCS 14–15: n = 26, and GCS 8–13, n = 0).

However, in our opinion, GCS is not appropriate and sufficient to describe a patient’s psychological and intellectual condition in the context of selection for AC, although commonly used to define neurological status [3, 4].

It may be surprising that even patients with previous psychiatric diseases, as well as those with a poor performance status (Karnofsky scale: < 70 points), were selected for AC and CS in other centres.

A significant correlation between an increase in intraoperative emotional intolerance, and further complications (uncooperativeness, respiratory insufficiency, conversion to general anaesthesia with intubation, or other instrumental upper airway support) during AC and CS, below 70 points of the Karnofsky scale has been noted [5].

This issue was addressed in other studies, which included patients with various neurosurgical procedures of AC/CS, based on dexmedetomidine sedation [5–7].


AC under dexmedetomidine-based CS is routinely performed in our centre.

To date, we have operated on about 70 patients for brain tumour resection, and we noted no adverse events.

All those procedures were completed successfully without conversion to general anaesthesia or any impact on respiration.

The psychological, psychiatric, and intellectual risk factors of adverse events associated with AC under CS were also of interest to us, but they will be presented in a separate publication.

Patients with severe comorbidities are at higher risk for conversion to general anaesthesia and instrumental airway support, during AC/CS.

This includes obese (BMI 30–35) and severely obese patients (BMI 35–40).

The issue is that surgery close to eloquent areas of the brain poses the risk of injury and postoperative disability.

AC increases the chance of the best postoperative neurological and intellectual result, preservation of multilingual skills, instrument playing, artistic skills and personality structure.

To date, only intraoperative performance helps to preserve these skills.

It is better to open up the chance for the patient than to risk irreversible disability and social disclosure.

The study by Garavaglia et al. [ 8] presented three cases of successful AC under CS: one with severe obesity, one with asthma and one with a lung tumour.

Recently other authors [9] presented a unique case of a patient with Eisenmenger syndrome who underwent two operations within a short period: the first under general anaesthesia and the second, successful AC/CS for resecting a large cyst in the third ventricle that was causing obstructive hydrocephalus and a risk of a brain inclination.


We agree that “difficult airways” is the “pearl” of AC.

The head fixed in the Mayfield clamp makes it challenging to instrumentally support the upper airways.

This procedure requires constant high attention, preparation and training of all surgical team members.

Only staff (such as the neuro-anaesthesiologist and anaesthetic nurses) who are aware and experienced in AC/CS nuances can perform such procedures.

Manual support through a face mask, nasopharyngeal, oropharyngeal tubes, laryngeal mask airway (LMA), videolaryngoscope, and fibrescope must be on hand, ready to be used by trained personnel, if needed.

This is recommended in all anticipated and unexpected difficult intubations [10].

In the presented cohort of patients, we based our anticipation of difficult intubation on standard criteria (Mallampati classification, thyromental distance, head and neck movement, inter incisor gap) and the above-mentioned instrumentation was always prepared.

To date, there has been no need to support upper airways in presented cases, as well as in all other AC/CS cases for brain tumour resection in our centre.

A report by Gruenbaum et al. [ 11] studied and presented the successful, fast, and useful ways of upper airway support during AC.

This report showed that the most successful and fastest method (32 seconds) was LMA (laryngeal mask), followed by intubation on bougie/through LMA insertion.

Videolaryngoscopic intubation and nasal/fibrescope intubation took longer (60–90 seconds and 70–120 seconds, respectively).

Cricothyroidotomy was effective only in 40% of cases in the context of ventilation, whereas tracheotomy done by an experienced surgeon was more effective [12].

Respiratory insufficiency, even asystole, was reported by some authors, during AC [12, 13].

Various factors can cause respiratory insufficiency, not only the sedative drugs, as commonly believed, but electrical stimulation, neurophysiological monitoring, aspiration, epilepsy with trismus and tongue biting with bleeding, severe comorbidities, obesity, other rear diseases, and medications [13, 14] All the above aspects should be analysed individually for candidates for AC [15].


Patient positioning for neurosurgical procedures is dictated by the need to assess brain lesions and the neurosurgeon’s preference.

In some cases, one can discuss altered positioning, if it is possible.

Lateral, park bench, prone, semi-sitting, and sitting positions are commonly used in neurosurgery.

The need for upper airway instrumentation in prone and park bench positions is of the highest risk of failed intubation and ventilation.

In our centre, no patients were operated on in the prone position.

In the paper, it was given as the concern of anaesthesiologists.

However, the study of Takami et al. [ 5] presented cases in lateral, park bench, sitting and semi-sitting positions for AC/CS.


In our study [1], small doses of fentanyl or midazolam were used for patient comfort only for the closing phase of the surgery if needed.

Five patients were given 0.05–0.10 mg of fentanyl in boluses of 0.05 mg and two patients received 1.0 mg of midazolam when neurophysiological and psychological assessments were finished.

No impact on respiration was observed.

Other reports on AC/CS show no adverse impact on such management [5, 9].

We did not use oxycodone during the surgery; it was used for postoperative pain control, but from observations on ropivacaine with adrenaline scalp block, excellent pain control up to 8–12 hours was possible.


We believe that the development of robotic surgery opens a new approach to anaesthetic management, and AC/CS is becoming common for more neurosurgical procedures.

Even recently, CS has been used for other surgery, such as deep brain stimulus: for Parkinson’s disease, obsessive-compulsive disorder, severe obesity, depression, psychiatric diseases, and many others.

The indications for intraoperative neuro-psycho-monitoring are still increasing.

There is an urgent need to develop a mode of anaesthetic management that is safe and comfortable for the patient, and that is suitable for all groups of patients, including those with severe comorbidities.

We hope that our study is a small step in this direction.


Citrus, like many other woody species, flower profusely.

In the Mediterranean area, flower induction takes place in autumn/ winter and the main blossoming in spring (Sherman and Beckman, 2003).


Current knowledge discriminates between exogenous and endogenous components for regulating flower- ing biology in citrus (Krajewski and Rabe, 1995; Martínez-Fuentes et al., 2004).

The former mainly includes climatic factors.

Thus, environmental cues such as temperature or photoperiod, and stress conditions (e.g. water deficit or sal- inity), have been reported as modulators of flowering responses (Agustí, 1999; Valiente and Albrigo, 2004).


On the other hand, endogenous factors are essentially genetic and/or hormonal.

Phytohormones, such as cytokinins, polya- mines or gibberellins, are known to participate to a certain extent in the physiological processes regulating flower induc- tion or differentiation (Koshita et al., 1999).

In particular, gibberellins have been traditionally considered as essential inhibitors of flower bud induction (Mutasa-Gottgens and Hedden, 2009).


In addition, the presence of fruit has also been found to be an inhibitor of flowering in fruit trees.

The response of flower- ing to fruit load has been reported in numerous species (Garner and Lovatt, 2008; Spinelli et al., 2009; Rosenstock et al., 2010), including citrus (Monselise and Goldschmidt, 1982).

This behaviour basically consists in the fluctuating production between heavy fruit yields (on year) followed by scarce ones (off year).


Moreover, the inhibitory effect of fruit in flower for- mation depends on both the number of fruits developed and the harvest date (El-Otmani et al., 2004; Martínez-Fuentes et al., 2010).

Hormonal factors, competition for nutrients or even changes in carbohydrate and mineral status (Goldschmidt et al., 1985; Valiente and Albrigo, 2004; Baninasab et al., 2007; Rohla et al., 2007) appear to participate in the regulation processes, although the way in which the presence of fruit affects flowering and the nature of the regulatory mechanisms remains unknown.


Recently, the development of genomic and transcriptomic tools has contributed to a better understanding of the metabolic and molecular processes involved in floral biology.

Most of our knowledge about flower induction has come from studying flowering regulatory genes in Arabidopsis thaliana (Komeda, 2004).

These genes appear to be extraordinarily conserved in woody species (Brunner and Nilsson, 2004), and previous research has demonstrated that many of them even share roles and/or metabolic pathways (Greenup et al., 2009).

Moreover, current evidence assumes that flowering is the result of complex interactions at the metabolic and molecular level involving multiple promoter and inhibitor genes (Moon et al., 2005; Michaels and Michaels, 2009).

Regarding citrus, several studies have recently been conducted to eluci- date the molecular mechanisms involved in flower formation and differentiation.

A first approach on citrus was developed by Peña et al. ( 2001), who demonstrated through plant trans- formation the role of APETALA1 (AP1) and LEAFY (LFY) genes in juvenile phase development.

Later studies have ident- ified and/or isolated in this species these (CsAP1, CsLFY; Pillitteri et al., 2004b) and other regulatory genes involved in both the determination of the flowering time and floral iden- tity processes (see Dornelas et al., 2007).


The regulatory role of the FLOWERING LOCUS T (FT) gene has been identified in numerous species (Turk et al., 2008; Zhang et al., 2010) including citrus (Endo et al., 2005; Nishikawa et al., 2007), and the encoded protein (FT protein) associated with the mythic 'florigen' (Yu et al., 2006).

Other genes, like CONSTANS (CO) or SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) have been reported to integrate signals from different pathways and, at least in Arabidopsis, are involved in promoting vegeta- tive to reproductive tissues (Borner et al., 2000; Lee et al., 2000; Onouchi et al., 2000; Komeda, 2004).

Specifically, CO participates in upstream and complex regulatory pathways, whereas SOC1 appears to act downstream (Dornelas et al., 2007).


In contrast, FLOWERING LOCUS C (FLC) represses flowering; high transcript levels have been found in late- flowering mutants, suggesting a central role of this gene in the control of flowering time, mainly through the vernalization pathway (Sheldon et al., 2000; Michaels et al., 2005).


Even though other repressor genes of flowering, like TERMINAL FLOWER 1 (TFL1), have been isolated from 'Washington' navel sweet orange (CsTFL; Pillitteri et al., 2004a) and corre- lated positively with juvenility, rigorous information about the function of FLC in citrus is not yet available.


In summary, alternate bearing is the result of complex meta- bolic and molecular regulatory pathways affecting flowering induction and floral identity.

The phenomenon has been largely explained as a crop load dependency and, although the factors modulating the processes involved have recently been studied for diverse species and key genes regulating flow- ering identified, we lack knowledge about the effects of crop load and the molecular mechanisms involved.

In this work, for the first time, the effects of fruit on the expression of puta- tive homologues of genes involved in flowering pathways were analysed to provide insight into the molecular mechanisms underlying alternate bearing in citrus due to crop load.


This study involved field grown 12-year-old trees of 'Moncada' mandarin [Clementina 'Oroval' (Citrus clementina Hort. ex Tan.) × 'Kara' mandarin [C. unshiu (Swingle) Marcow. × C. nobilis Lour.] trees, grafted onto 'Carrizo' citrange [C. sinensis Osbeck × Poncirus trifoliata (L.) Raf.] rootstock, planted 5 m × 5 m apart.

Experimental fields were located in the IVIA Research Station (Moncada, Spain).

Trees of this cultivar exhibit a marked alternate-bearing behaviour.


To examine the effect of fruit load on flowering, 25 trees were randomly selected for their uniformity in size and vigour at spring.

Total yield per tree was determined by count- ing and weighing all fruits at harvest (April), and flowering intensity was evaluated in spring as follows.

Four branches per tree of three ages (late spring, summer and autumn sprouts) with some 300 nodes per branch were previously selected.

Both the number of sprouted nodes and sprouts were counted.

The flowers per sprout were also counted, obtaining the results as the number of flowers per 100 nodes to compensate for the differences in size of the selected branches.


Defruiting experiments were performed on another set of 24 trees using four levels of fruit removal (0, 33 %, 66 % and 100 %).

Treatments were performed at the onset of stage II of fruit development (July).

A randomized complete-block design was used in the experiments.


From early September to the end of February, 30 fully developed mature adult leaves per tree from on (fully loaded) and off trees (without fruits) were collected for RNA extractions.

Samples were pooled into three groups, and immediately ground and stored at - 80 8C until analysed.


Total RNA was isolated from frozen tissue using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany).

RNA samples were treated with RNase free DNase (Qiagen) through column purification following the manufacturer's instructions.

RNA quality was tested by OD 260 /OD 280 ratio and gel electrophoresis.

RNA concentration was determined by fluorometric assays with the RiboGreen dye (Molecular Probes, Eugene, OR, USA) according to manufacturer's instructions.

Three fluorometric assays per RNA sample were performed.


Quantitative real-time RT-PCR was performed with a LightCycler 2 . 0 Instrument (Roche Diagnostics, Basel, Switzerland) equipped with LightCycler Software version 4 . 0.

One-step RT-PCR was carried out.

Reactions con- tained 2 . 5 units of MultiScribe Reverse Transcriptase (Applied Biosystems, Carlsbad, CA, USA), 1 unit of RNase Inhibitor (Applied Biosystems), 2 mL LC FastStart DNA MasterPLUS SYBRGreen I (Roche Diagnostics, Basel, Switzerland), 25 ng total RNA and 250 nM of the specific forward and reverse primers of each gene in a total volume of 10 mL. Incubations were carried out at 48 8C for 30 min, 95 8C for Muñoz-Fambuena et al. - Fruit regulation of flowering gene expression in citrus 512 10 min followed by 45 cycles at 95 8C for 2 s, 58 8C for 8 s and 72 8C for 8 s. Fluorescent intensity data were acquired during the 72 8C-extension step and transformed into relative mRNA values using a 10-fold dilution series of an RNA sample as a standard curve.

Relative mRNA levels were then normalized to total RNA amounts as previously described (Bustin, 2002; Hashimoto et al., 2004) and an expression value of 1 was arbi- trarily assigned to the first sample of the on trees.

Specificity of the amplification reactions was assessed by post-amplification dissociation curves and by sequencing the reaction product.


Putative genes were identified through homology search with related genes from an EST database of a random 5 ′ 'Clemenules' mandarin (C. clementina Hort.

ex Tan.) full- length cDNA library (Terol et al., 2007).

Synthetic oligonu- cleotides were designed to amplify the gene from the selected clones and, as stated before, sequenced for confirmation.

Details about the forward and reverse primers are listed in Table 1.


Parameters were statistically tested by analyses of variance (ANOVA), using the least significant differences (LSD) test for means separation.

The experimental data were analysed with Statgraphics Plus 5 .

1 software (Statistical Graphics, Englewood Cliffs, NJ, USA).


A significant inverse relationship between preceeding fruit load and flowering intensity was found in 'Moncada' mandarin (r ¼ -0 . 93; P ≤ 0 .

05; n ¼ 25; Fig. 1).

Considering the results, the larger the crop load the lower the flowering intensity, with a breaking point of about 50 kg tree 21 .

Above this fruiting value, flowering was independent of crop load and paralleled nearly nil values.


Although statistically significant, this relationship does not imply causality, therefore further experiments were carried out to demonstrate the direct effect of fruit removal upon flow- ering.

As expected, control on trees (non-defruited, fully loaded) showed the lowest number of flowers (0 . 5 flowers/ 100 nodes, on average), in comparison with those completely defruited, which presented the highest number of flowers (142 flowers/100 nodes).

Intermediate fruit loads (33 % and 66 % defruited trees) resulted in intermediate flowering intensities (Fig. 2).


The effect of fruit removal on flowering was also evident on fruit set and yield assessment.

The higher the flowering inten- sity, the larger the crop load (data not shown).

The magnitude of the response, however, depended on the time of fruit removal.

Thus, removal of all fruits in August, September or October did not affect flowering in spring (100 - 135 flowers/ 100 nodes; Fig. 3); however, when fruit removal was per- formed from November onwards, a dramatic inhibition of flowering was observed the following spring (,10 flowers/ 100 nodes).


The time-course of CiFT expression in leaves throughout the study was strongly affected by fruit load (Fig. 4).

Significant differences in mRNA transcripts were detected between on and off trees from October onwards.

The expression in off tree leaves increased progressively, becoming more than 10-fold higher than that of on tree leaves in December, and remaining almost constant up to late in February.

CiFT tran- scripts in on tree leaves did not significantly vary within the study period.


The time-course of SOC1 relative expression in leaves was also higher in off trees than in on trees (Fig. 5).

Differences were statistically significant from early September to mid-December, becoming highest in November (close to 50 % higher for off trees).

From early January onwards, differ- ences between treatments were not statistically significant.


Figure 6 shows the time-course of FLC expression in leaves from on and off trees.

From September to mid-December, no differences in gene expression between treatments were found.

In January, however, levels of mRNA transcripts mark- edly increased in on trees.

From January until the end of the study, expression in on tree leaves remained between 1 .

6- and 2 .

8-fold higher than in off tree leaves.


Expression of CsTFL in leaves was slightly reduced from September to mid-November; afterwards, it continuously increased up to the end of February, when it was .3 times the amount measured in November (Fig. 7).

No significant differences were found between leaves from on and off trees during the study period.


CsAP1 and CsLFY revealed different patterns of change in response to fruit load (Fig. 8).

CsAP1 expression remained almost constant from early October up to the middle of December.

During this period, expression values were 3 - 5 times lower in on trees than in off trees.

From December onwards expression increased in both cases and, although minor in magnitude, significant differences between on and off trees were also found until the end of February.


On the other hand, CsLFY expression progressively increased from September to the middle of December (15- to 20-fold).

After a transitory reduction in January, expression considerably aug- mented towards the end of February, reaching values between 30 and 50 times those registered in September.

Differences between on and off trees were only significant at the end of the study.

In late February, CsLFY expression in off trees was significantly higher than that found in on trees (close to 20 %).


Alternate bearing has been associated primarily with the pres- ence of fruit (Verreynne and Lovatt, 2009; Martínez-Fuentes et al., 2010).

According to the literature, it is assumed that crop load alters both flower induction and floral bud differen- tiation (Valiente and Albrigo, 2004).

Particularly, in citrus, flower induction has been reported to occur late in autumn, whereas differentiation occurs afterwards (Iglesias et al., 2007).

Recent molecular approaches support this scheme, dis- tinguishing between genes regulating flowering induction and those regulating floral differentiation processes (Tadeo et al., 2008).

The present results indicate that genes regulating flower induction are strongly related to fruit load in alternate- bearing citrus trees.


Fruit load acts as a strong inhibitor of flowering in numerous woody fruit tree species including citrus, although the responses vary among species and cultivars (Monselise and Goldschmidt, 1982; Valiente and Albrigo, 2004; Albrigo and Galán, 2004).

The present data obtained for 'Moncada' man- darin confirmed, once again, a non-linear fruit load - flowering intensity relationship (Fig. 1).

However, since this relationship does not necessarily imply causality, convincing evidence that fruit load is directly responsible for reducing flowering inten- sity was provided by means of defruiting treatments.


Trees maintaining all developed fruits up to maturation hardly flow- ered (5 flowers/100 nodes, on average), whereas those fully defruited at the onset of stage II of fruit development flowered profusely (142 flowers/100 nodes, on average).

Trees defruited at an intermediate intensity (33 % and 66 % of developing fruitlets) flowered intermediately as well.

However, because no differences were found between 33 % and 66 % of fruit removal (16 and 22 flowers/100 nodes, respectively) the effect does not appear to be strictly quantitative.


These results support the hypothesis that the fruit load - flower- ing intensity relationship is not a linear function and this coincides with previous reports suggesting that there might be a threshold value for crop load, dependent on the variety and physiological status, above which flowering is strongly inhibited (Agustí et al., 1992; Martínez-Fuentes et al., 2010).


It has been previously reported that flower inhibition due to crop load also depends on the length of time the fruit remains on the tree (see review by Monselise and Goldschmidt, 1982).


Considering the present data for 'Moncada' mandarin, fruit Sep Oct Nov Dec Month Relative CsTFL expression Jan Feb 1 2 On Off Muñoz-Fambuena et al. - Fruit regulation of flowering gene expression in citrus 515 remaining on the tree did not affect return bloom (100 - 120 flowers/100 nodes) up to November; however, fruit remaining on the tree from November onwards dramatically reduced flowering (values close to 0).

Therefore, effective inhibition time of fruit load began between October and November.

This period has been associated with the fruit reaching its maximum size (Martínez-Fuentes et al., 2010), or with peel ripening (García-Luis et al., 1986).

In any event, fruit drasti- cally inhibits flowering from November onwards, suggesting that there is a point of no return for induction of quiescent buds, and that some irreversible physiological, metabolic or molecular events induced by presence of fruit must be respon- sible for inhibition.

This hypothesis is supported by the fact that bud sensitivity to gibberellic acid (GA 3 ) inhibiting flower- ing occurs at this moment (García-Luis et al., 1986).


The mechanism whereby fruit load affects flowering intensity is not completely understood, although several regulatory factors have been described.

Early observations linked carbo- hydrate and nitrogen metabolism to the process (Goldschmidt et al., 1985; Lovatt et al., 1988); however, recent studies demon- strated that carbohydrate or nitrogen status are involved in nutri- tional or storage adjustments rather than in the floral process directly (Reig et al., 2006; Martínez-Fuentes et al., 2010).

Several studies have linked flowering intensity to bud sprouting, showing that changes in flowering intensity paralleled changes in the summer/autumn shoot number (Verreynne and Lovatt, 2009; Martínez-Fuentes et al., 2010), and also illustrated that the higher the fruit load the lower the number of sprouted nodes in spring (Martínez-Fuentes et al., 2010).

Additionally, environmental factors can modulate flowering through modifications in the physiology of shoot development or even in key metabolic path- ways (Agustí, 1999).

Nonetheless, knowledge about factors affecting flowering has considerably increased, but data do not provide enough information to understand the mechanisms through which the fruit controls the process of flowering.


Recently, molecular and genomic approaches have been con- sidered important tools to shed light on the complex physiologi- cal and metabolic pathways leading to flowering.

In recent years, numerous flowering-gene promoters and inhibitors have been identified, isolated and characterized.

Extensive research has been done in A. thaliana, for which the balance between promo- ters and inhibitors is decisive for the adequate determination of flowering time and floral identity (Chon and Yang, 1999; Kobayashi et al., 1999).

However, in woody tree species, little has been done on this subject.

The results presented herein regarding the expression of flowering genes affected by fruit load offer an insight into the molecular mechanisms underlying alternate bearing in citrus trees.


In several species, flowering ability has been demonstrated to be influenced by the integration of environmental signals from the photoperiod and vernalization pathways (Onouchi et al., 2000; Amasino, 2005; Sheldon et al., 2009), mainly modulated by two floral integrators, the FT and the SOC1 genes (Kardailsky et al., 1999; Borner et al., 2000; Lee et al., 2000; Samach et al., 2000).

Both genes have been described as floral promoters and their overexpression induces early-flowering phenotypes (Lee et al., 2006; Sreekantan and Thomas, 2006; Zhang et al., 2010).

The FT gene has been demonstrated to be a pivotal factor controlling flowering period in numerous species (Faure et al., 2007; Chab et al., 2008; Hisamoto et al., 2008; Zhang et al., 2010).

The present results support this hypothesis and further relate it to the effects of fruit load in citrus trees just as autumn/winter temperature enhances its expression (Nishikawa et al., 2007).


Leaves from off trees (high-return bloom-flowering in spring) showed significantly increased mRNA transcript levels as compared with those from on trees (low return bloom).

Thus, whereas on trees showed stationary basal levels of expression, a progressive increase in CiFT levels was observed in leaves from off trees (Fig. 4) until December, concomitantly with a higher flowering rate the following spring (Fig. 2).


These results demonstrate, on the one hand, that an increased FT protein constitutes a signal per se that exports from leaf to the shoot apical meris- tem, where floral differentiation takes place (Notaguchi et al., 2008) and, on the other, that a translated FT protein can be translocated to the floral meristem at any time (Lin et al., 2007; Turck et al., 2008).

Nevertheless, the translocation pathway followed by FT protein into the apex remains unknown.


Although not always significant, SOC1 also showed higher expression levels in leaves from off trees compared with those registered for on trees, particularly during the floral induction period (Fig. 5).

Lee and Lee (2010) reported that constitutive expression of SOC1 promotes early flowering, while recessive loss-of-function seems to delay flowering (Onouchi et al., 2000).

Although isolated in only a few plant species, highly conserved homologues of this gene have been identified in numerous species, including citrus, in which the constitutive expression of several SOC1-like homol- ogues induces early flowering and delays senescence of floral organs (Tan and Swain, 2007).

In this sense, the present results confirm the role of this gene in flowering resulting from alternate-bearing adult trees.


Unlike the functions attributed to SOC1 and FT genes, FLC has been described to encode a MADS-domain protein able to repress flowering (Michaels and Amasino, 1999).

The present data showed no differences in FLC activity between on and off trees until December (Fig. 6).

From this time onwards, there was a progressive increase in transcript levels in leaves from on trees, whereas those from off trees showed no change or even a slight decrease.


Some authors have pointed out that ver- nalization promotes flowering through a permanent epigenetic repression of FLC (Michaels and Amasino, 1999), probably through histone methylation and changes in chromatin confor- mation (Bastow et al., 2004; Sung and Amasino, 2004).

In the present study, trees with increased amounts of FLC mRNA transcripts near spring corresponded to on trees that did not flower.

Additionally, previous reports have indicated antagon- istic effects of flowering promoters and FLC on the expression of target genes leading to flowering.


The study of regulatory pathways demonstrates that this gene is located upstream along the major pathways, since FT overexpression does not appear to affect FLC expression (Moon et al., 2005; Lee and Lee, 2010).

Likewise, it has been proposed that elevated levels of FLC expression may be responsible for reductions in FT activity (Michaels et al., 2005).

In this context, the marked increase in FLC measured in the on trees from December onwards (Fig. 6) might be related to the suppression Muñoz-Fambuena et al. - Fruit regulation of flowering gene expression in citrus 516 of CiFT activity in their leaves compared with off trees (Fig. 4) and, therefore, with the inhibition of flowering.


Moreover, the results show that SOC1 expression increased in off trees before the sharp increase in CiFT, so the activation pathways appear to work, at least partially, autonomously; fur- thermore, from November onwards, SOC1 expression did not parallel the increased CiFT gene expression.

This is not unusual since, at least partially, self-determining regulatory mechanisms for FT and SOC1 activity have been reported recently (Lee and Lee, 2010).

Therefore, this hypothesis can be extrapolated to the molecular mechanisms affecting flower- ing through effects of fruit load.

Moreover, whereas CiFT expression was significantly higher in off trees as compared with on trees until the end of February, significant differences in SOC1 expression disappeared by the beginning of January.


Although TFL1 has been described as a crucial floral timing regulator in several species (Shannon and Meeks-Wagner, 1991; Liljegren et al., 1999), in the present study no differ- ences in CsTFL expression dependent on fruit load were found (Fig. 7).

This gene was identified and isolated in Citrus sinensis (Pillitteri et al., 2004a) and has been proposed to participate in the development and maintenance of vegeta- tive growth, repressing flowering in several plant species (Esumi et al., 2010; Mohamed et al., 2010).

In addition Nishikawa et al. ( 2009) have reported no variations in the expression of this gene during induction and flower bud devel- opment, neither in trifoliate and deciduous Citrus-like species (P. trifoliata) nor in Satsuma mandarin (C. unshiu), indicating that this gene is related to juvenility processes rather than to annual floral transition.


Since there were no differences between on and off trees regarding CsTFL expression, differ- ences in flowering as a consequence of fruit load do not appear to be dependent on this gene.


Finally, AP1 and LFY genes have been reported to promote flowering in diverse species including citrus, although their primary role appears to be linked to the determination of floral identity (Pillitteri et al., 2004b).

Although transgenic approaches have demonstrated that both genes strongly interact with other physiological processes, such as competition for nutrients, their constitutive expression per se reduces the juve- nility period in transgenic citrus (Peña et al., 2001; Duan et al., 2010).

In particular, AP1 seems to be more effective and dynamic than LFY in the induction of flowering (Peña et al., 2001), orchestrating floral initiation by repressing the action of inhibitors at the level of the meristem as stated by Kaufmann et al. ( 2010).


The present results showed a reduced expression of CsAP1 in leaves in response to the pres- ence of fruit (Fig. 8).

Differences between the levels of expression in leaves from on and off trees were significant during the whole study period despite the reduction in these levels from January onwards.


It is noteworthy that LFY activity has been associated with the control of floral meristem identity in Arabidopsis (Weigel et al., 1992).

Moreover, recent studies on fruit trees, including citrus, demonstrated that once floral identity is determined, high LFY expression levels are almost limited to reproductive organs (Pillitteri et al., 2004b).

This observation might also be linked to the absence of differences in CsLFY expression in leaves from on and off trees between September and January.


The significantly higher values found in off trees at the end of February support the main role of this gene on bud differentiation and/or floral identity rather than on inductive processes.


In conclusion, in Citrus fruit load inhibits flowering by repressing CiFT and SOC1 expression in leaves during the floral bud induction period, whereas CsTFL and FLC expression does not seem to be associated with fruit load.

Fruit load reduces CsAP1 gene expression in leaves during the floral bud induction period, although differences between on and off trees were attenuated from January onwards, indicat- ing the onset of floral differentiation.

This hypothesis is also reinforced by the significant increase in CsLFY expression found in leaves from off trees only in late February.

The FLC-increased expression in on trees from early winter onwards might well be related to the suppression of CiFT expression in their leaves and, therefore, with inhibition of flowering.


Studying a process in a new species often relies on focusing our attention to a candidate gene, encoding a protein similar to one with a known function.

Not all the choices seem to be prudent.

This Viewpoint includes an overview of issues that are encountered during research of candidate genes.

Defining a match for a gene of interest, deciding whether variation in ESTs or RNAseq data for a certain transcript, represent more than one gene.

The problem of incorrect annotation of genes due to incorrect in-silico splicing, is also mentioned.

The author’s humble opinion on how to deal with these issues is provided.

The vast amount of new sequence data provides us with great possibilities for giant leaps in our understanding.

Still, we cannot afford to skip over the tedious steps required to confirm that we are indeed studying the correct gene, and try to be sure that the complex expression pattern we observe is not a composite of several genes.


One rationale behind studying ‘model’ plants (MPS) such as arabidopsis is that different plant species are likely to use conserved mechanisms to control development, metabolism and other processes.

By learning from one species that is easy to study, we might extrapolate these findings to different, more complex species, which are either more important to agriculture, or simply our ‘favourite’ species (OFS).

For example, while flowering of different plant species is mediated by different internal and external cues, it seems to be triggered by a common protein, FLOWERING LOCUS T (FT), which functions as a universal ‘florigen’ [1].

The MADS box proteins that confer organ identity in flowers (termed the ABC model) are another example of conserved function [2].

It is obvious that not everything will be the same among species, and the differences help explain why flowering plants are so diversified.

Once we decide to study a certain event in OFS, we might begin by presuming nothing and start our studies with a clean slate.

Many choose to also use a parallel approach in which they study ‘candidate’ genes that encode proteins that were functionally characterized in MPS.

This Viewpoint discusses problems that might rise in the course of picking such candidate genes.


If X and Y are identical twin dogs and someone scanned all dogs on the planet for the one that is most similar (in genome sequence) to X, they should end up with Y. If X was in a room with one more dog (Z) and several humans, a scan limited to the room would probably identify Z as most similar to X. The depth of the search clearly depends on the available dataset.

If I want to identify, in OFS, a gene encoding a protein most similar in sequence to protein X from MPS, I would need to have access to the full genome of OFS, to identify the best match.

Still, I might be lucky and identify a gene encoding a protein orthologous to X from a small dataset.

When can I assume that the gene I identified indeed encodes a protein that has a similar role to the one described for protein X in MPS?

There is no straightforward answer to this question and there are different points of view regarding how rigorous the analysis should be before making such a statement.

If XMPS and XOFS share extended homology, and mutations in each of the genes cause similar phenotypes, one might assume that these are orthologous genes which have originated from the same gene in their common ancestor and share the same function.

Reaching this result would depend on how easy it is to obtain loss of function mutations in both species, and whether or not there are redundant genes that might mask the phenotype of loss of function.

In many species the genome has gone through duplications or has become polyploid.

Thus, reaching a loss of function phenotype becomes even more difficult.

Without loss of function phenotypes, similar expression profiles can also strengthen a choice of an orthologue among paralogues [3].

Clearly, homology within functional domains is a better indicator than overall similarity, since a loss of an active site would make a paralogue into a pseudogene [4].


In a recent paper, we described for the first time the effects of fruit on the expression of putative homologues of genes involved in flowering pathways.

It was our aim to provide insight into the molecular mechanisms underlying alternate bearing in citrus.

However, a bioinformatics-based critique of our and other related papers has been given by Samach in the preceding Viewpoint article in this issue of Annals of Botany.

The use of certain bioinformatic tools in a context of structural rather than functional genomics can cast doubts about the veracity of a large amount of data published in recent years.

In this response, the contentions raised by Samach are analysed, and rebuttals of his criticisms are presented.


Alternate bearing is a result of complex metabolic and molecular regulatory pathways in which flowering-related genes are strongly implicated.

In a recent paper published in this journal we reported, for the first time, the effects of fruit on the expression of putative homologues of genes involved in flowering pathways.

It was our aim to provide insight into the molecular mechanisms underlying alternate bearing in citrus (Citrus clementina) due to crop load.

For detailed information, please refer to our original paper [1].


The main conclusion derived from our study was that fruit modulates seasonal expression of flowering genes in alternate-bearing ‘Moncada’ mandarin: novel and original research in the context of fruit crop physiology (indeed, the publication was awarded a Graduate Prize by the journal).

The study of the expression pattern of flowering-genes of on (fully loaded) and off (without fruit) trees revealed that mainly CiFT and also floral-identity genes (CsAP1 and CsLFY) are highly involved in the process.

No reference to choosing any new developmental regulator, as Samach [7] generalizes, was included in our manuscript.


Moreover, he claims that ‘the vast amount of new sequence data provides us with great possibilities for giant leaps in our understanding’, and he globally criticizes some current, frequently used methodological approaches.

It is certainly the case that in recent decades an astonishing advance in the development of new databases and bioinformatic tools and platforms has taken place [5].

Nevertheless, current genome programs generate large amounts of data that require significant processing, storage and delivery to the research community [8], not always resulting in a precise or complete annotation of genes and associated proteins – especially so if referred to EST collections.


Previous publications have already warned about the current limitations of bioinformatics [6] and in this context it is well known that, as the volume of sequence data increases exponentially, the number of genes of unknown function – and, therefore, the large amount of associated uncertainties, gaps or mismatches – does as well [4].

It is fairly easy to understand how this excess of information may be conveniently interpreted when introduced into functional research, and likewise conclusions may be exaggerated in scenarios of in silico gene prospecting.


In our opinion, however, this potential lack of precision and the continuous improvement of bioinformatic procedures should not be exploited to spread doubts about the conclusions of functional studies that are just focused on the role of previously described genes.


In his Viewpoint article, Samach alerts the reader to the problems that arise when mixing new databases with old ones and their corresponding notations.

In the following paragraphs we will give concise evidence as to why the conclusions we presented previously are as precise as possible in terms of functionality, the main goal of our research.


(1) To analyse the expression of those genes previously identified and sequenced in citrus based on an EST collection, the primers we used were selected for the specific amplification of the targets according to the current literature and the corresponding public annotation.

Any new developmental regulator was studied.

Just as an example to illustrate that Samach’s assertions are not necessarily as precise as stated, we point out that when you BLAST the EST supposedly containing CiFT to public databases (i.e. NCBI) the unequivocal output is, precisely, CiFT.

In addition, it is worth mentioning that in combining in silico the old with new and other particular non-published databases, Samach appears to ignore that the increase in the number of genes of a given family is not a reason to invalidate the functionality of a target, previously-annotated gene.


(2) To analyse the expression of those genes not yet identified or annotated, a consensus sequence formed by all EST homologues (from the Citrus Functional Genomics Project; http://bioinfo.ibmcp.upv.es/genomics/cfgpDB/) to the target Arabidopsis gene was built [2], and a specific primer was designed for amplification.

This methodology (with its understandable limitations) is not new and in fact it is widely represented in the bibliography.


(3) In order to provide transparent information for the reader, we decided to include in our study, together with the sequence of the primer, a table with details about the notation of the EST with highest similitude to the target gene previously described (see point 1) or the consensus sequence designed (point 2).

The fact that this sequence was or was not annotated in the referenced database is not so relevant from a functional perspective.


(4) Finally, the use of sequences from new, published databases (e.g. Aleza et al., 2009) instead of being from previous ones would only affect the nomenclature and codes in our published table.


All things considered, we understand that the ultimate goal of functional genomics is to integrate large amounts of data so as to increase basic knowledge about key biological processes.

Our study into the molecular mechanisms underlying alternate bearing in fruit trees is a good example – with the known limitations in the use of EST collections.

And we hope that further studies supported with new data will confirm or improve our published results – which is, after all, the ultimate goal of scientific research.


Chronic lower back pain is well known as a public health epidemic.

In highly developed countries, it is one of the top 3 causes of degradation in quality adjusted life years, along with ischemic heart disease and chronic obstructive pulmonary disease [1].

While lumbar spine pathology is an important cause of chronic lower back pain, substantial evidence suggests that not all low back pain is due to lumbar spine pathology.

The SI joint is thought to be the source of pain in up to 30% of patients evaluated for chronic lower back pain [2-5].

Disorders of the SI joint may be the result of trauma, pregnancy, inflammatory arthritis, osteoarthritis or degeneration of the joint either de novo or after lumbar spinal fusion [6].

In the case of lumbar spinal arthrodesis, sacroiliac joint pathology may explain delayed postoperative pain or a failure for the patient to experience symptom improvement in the early postoperative period (failed back surgery syndrome) [7, 8].


Diagnosing the SI joint as the primary or sole pain generator (PG) can be complex as patients often present with a combination of low back, groin, gluteal, and/or leg pain and the symptom profile may mimic other disorders of the lumbar spine and hip [2, 9].

Additionally, some patients present with more than one pain generator within the lumbar spine-SI joint-hip axis, making the identification of the primary versus secondary pain generators more challenging [3].

Furthermore, SI joint imaging studies are typically neither sensitive nor specific to abnormalities in the absence of trauma, tumor, ankylosing spondylitis, or infection [10].


SI joint pain can be debilitating and treatment with non- operative care is often unsuccessful.

The impact of pain on persons living with the disease is similar to that associated with other prominent orthopedic conditions routinely treated surgically [11].

Furthermore, the economic burden of non- operative care is significant for Medicare as well as commercial payer entities with a 5-year estimated cost of $270 million for Medicare beneficiaries and a 3-year estimated cost of $1.6 billion per 100,000 commercial covered lives [12, 13].


Surgical treatment options for SI joint disorders have been unattractive until relatively recently.

Open arthrodesis, commonly performed throughout the 1900s, is now reserved primarily for traumatic pelvic ring fractures due to the invasiveness of the procedure, coupled with a high morbidity rate [14-16].

In recent years, several minimally invasive Rudolf and Capobianco techniques for fusing the SI joint have been introduced into the surgical repertoire [17-21].

MIS SI joint fusion for certain SI joint disorders (degenerative sacroiliitis and SI joint disruptions), specifically using a series of triangular titanium implants, has been shown to result in lower morbidity, including shorter operating times and hospital stays, fewer complications, a lower reoperation rate, and higher gains in patient quality of life compared to the open surgical method, as evidenced by a recent comparative cohort study [22].


The current body of medical literature substantiates positive short to mid-term clinical outcomes [17, 23-25].

However, no long-term clinical or radiographic outcomes have been published to date.

Herein we report 5-year clinical effectiveness, safety and radiographic outcomes in patients treated with MIS SI joint fusion for degenerative sacroiliitis or sacroiliac joint disruptions using a series of triangular, porous titanium plasma spray (TPS) coated implants (iFuse Implant System ® , SI-BONE, Inc., San Jose, CA) from a single center.


All consecutive patients who underwent MIS SI joint fusion between October 2007 and March 2009 at a single center were identified.

Prior to surgery, all patients were diagnosed with either degenerative sacroiliitis and/or SI joint disruptions using a detailed history, combination of physical provocative maneuvers specific to the SI joint, image-guided intra-articular SI joint injections and various imaging modalities [17].

MIS SI joint fusion was performed in all patients by placing a series of implants laterally across the SI joint, as previously described [17, 23].

Patients were contacted and asked to participate in a long-term evaluation, which included a clinical exam as well as an optional radiographic imaging component.

Patients signed a study- specific, IRB-approved consent form before beginning any study-related activity.


Patients were asked to reveal and discuss any further surgical treatment they received for SI joint, lumbar spine, pelvic or hip disorders.

A series of patient reported outcome instruments, described below, was also administered.

Participants who resided outside of a reasonable travel distance were given the opportunity to provide responses by phone or mail.

Patients who consented to the radiographic component of the study had both plain film radiographs (outlet and anteroposterior (AP) views) and computed tomography (CT) scans of the pelvis.

These imaging tests were used to assess implant position, evidence of lucency adjacent to the implant, qualitative increase in bone density adjacent to the implant, and presence of intra-articular osseous bridging.

The 5-year images were compared to those previously acquired closest to the one-year follow-up interval.


Data extracted from the medical charts included demo- graphics, diagnosed pain generators in the lumbar spine-SI joint-hip axis, pain treatments received, perioperative measures, adverse events, one-year imaging studies, and previously administered patient reported outcomes at 12- and 24-months postoperatively, described below.


Pain and functional outcomes were assessed in a prospective manner pre-operatively and at 12-, 24- and 60-months postoperatively.

Level of pain was assessed using a 0-10 visual analog scale (VAS).


Prior to the initial experience with the surgical procedure, a 9-question SI joint- related health outcomes survey was created with response domains taken from both the SF-36 and Oswestry Disability Index (ODI) (Fig. 1): pain level, the ability to perform light, moderate and vigorous activities, quality of sleep, lifting ability, happiness, social activities, and the effect of pain on social life [17].

A numerical rating scale of 0-10 with 0 representing no pain or difficulty and 10 representing the worst pain imaginable or severe difficulty was used for all domains.


Satisfaction with surgery was assessed in a binary fashion (yes or no) by asking if the patient would have the same surgery again for the same result.

The SI joint-related health outcomes survey and VAS were administered preoperatively and at 12- and 60-months postoperatively.


At 24 months, patients were contacted to assess SI joint pain on VAS.

The ODI was administered at the 60-month visit only.

Satisfaction and safety events were collected at all postoperative time points.


Demographic variables were tabulated and expressed as frequency and means with standard deviation, where appropriate.

A repeated measures analysis of variance (ANOVA) was used to compare VAS pain scores from baseline to all postoperative time points.

A paired t-test was used to assess improvement from baseline to the 60-month time point on the SI joint survey.

An unpaired t-test was performed to assess the effect of sex and history of prior lumbar spinal fusion on outcomes.

Statistical analyses were performed using R software [26].

Clinical improvement was defined using previously validated minimum clinically important difference (MCID) and substantial clinical benefit (SCB) values for back pain on VAS.

MCID is defined as a change of >2.0 points and SCB is defined as a 2.5-point decrease or a raw score of < 3.5 [27, 28].


Institutional Review Board approval was obtained before beginning this study.


1. How much pain are you in at this time?


2. How well are you able to perform light activities like walking a block or dressing yourself?


3. How well are you able to perform moderate activities like playing golf, walking half a mile, or dancing?


4. How well are you able to perform vigorous activities like running or moving furniture?


5. How much is your sleep disturbed by pain at this time?


6. How well are you able to lift items off the floor at this time?


7. How would you assess your level of happiness at this time?


8. How interested are you in socializing at this time?


9. Because of pain, how much is your socializing limited at this time?


Of 21 consecutive patients who underwent MIS SI joint fusion, 17 were available for follow-up and form the analysis cohort.

Of those not available, 2 had died unrelated to spine conditions, one was lost to follow-up and one suffered a severe neck trauma rendering the patient quadriplegic and unable to provide relevant data.

All available patients participated inthe clinical portion of the study and 15 of 17 (88%) agreed to participate in the radiographic component.


Mean subject age was 58 (±14) years (range 36-85), 77% were female and 47% had undergone lumbar spinal fusion prior to SI joint fusion (Table 1).

Slightly more subjects had the right SI joint treated (53%) compared to the left (41%), and one patient underwent bilateral treatment.

Mean operating time was 65 (±18) minutes, range (43-110).

There were no intraoperative complications.

Postoperative events, which primarily included hematoma (1), cellulitis (2), and deep infection secondary to diverticulitis (1), were previously reported in detail [17].


Improvement in pain was clinically and statistically significant at all follow-up intervals compared to baseline (all p<0.001) (Table 2).

All subjects who reached MCID also reached SCB.

The percentage of patients who achieved both MCID and SCB remained high at each time point (77%, 82%, and 88% at 12-, 24- and 60-month visits, respectively).

No statistical effect was found for sex, or history of lumbar fusion on pain improvement at any time point.

At 60-months, statistically significant improvement was seen in 6 of 8 domains of the SI joint survey instrument (Table 3): the ability to perform light, moderate and vigorous activities, sleep disturbance caused by pain, overall happiness, and the effect of pain on social life.

The ability to perform light, moderate and vigorous activities showed continual improvement from 12 months to the 5-year time interval.


Patient satisfaction scores obtained at the 12-month interval were unchanged at 2- and 5-years postoperatively; 82% (14/17) would have the same surgery again for the same result at all time points.


ODI scores were obtained at the 5-year follow-up only (Table 4).

Mean (SD) ODI score was 21.5 (22.7).

Fairbank categorized scores in terms of degree of disability, with 0-20 representing minimal disability and 21-40 representing moderate disability requiring conservative care only [29].

Results show the majority (71%) of subjects are living with minimal or moderate disability.


Pelvic AP and outlet view plain films radiographs and a pelvic computed tomography (CT) scan were performed on 15 subjects; 45 implants were assessed.

Imaging studies obtained at 5 years were compared to available studies acquired as close as possible to the one-year postoperative time point.


A qualitative comparison of 1- and 5-year pelvic plain film radiographs, including AP and outlet views, revealed no change in implant position (Fig. 2).

CT scans of the pelvis with axial, sagittal, and coronal reconstructions documented increased bone density circumferentially along three implant walls for all implants on both the iliac and sacral segments.

Evidence of osseous bridging across the SI joint was clearly seen on 13 of 15 (87%) of patients (Fig. 3).


On x-ray, what appeared to be full-length lucency (absence of bone adjacent to an implant) along the wall of the implant was consistently observed on at least one implant in all patients on AP view.

However, this observation was not evident on the outlet view.

Upon review of CT imaging, this apparent lucency was confirmed to be an artifact (Fig. 4).


Assessment and comparison of CT scans at 1- and 5-years revealed a consistent pattern of artifacts at the corners and periodically along the wall of an implant, which were non-progressive and unchanged in equivalent projections on the axial, sagittal and coronal sections.

A small area of true focal lucency was observed on CT scans in 4 patients; along the superior edge of the most cranial implant on the iliac side in 3 patients, and on the superior edge of the most caudal implant on the iliac side in one patient (Fig. 5).

Other findings included a regular pattern of sclerotic bone response at the implant entry point in the ilium, on primarily the superior implant (Fig. 6).

A detailed explanation of the physics of CT imaging of triangular titanium implants is outside the scope of this manuscript and will be reported separately.


Three subjects in the current cohort did not improve satisfactorily.

To understand why these patients failed to improve and to refine patient selection criteria for MIS SI joint fusion, an in-depth interview was performed for each patient.

Patient vignettes are described below.


Subject 1012 is a 72-year old woman who presented to the clinic complaining of low back and pelvic pain.

The subject's history included a successful total knee replacement as well as L3-L5 arthrodesis for degenerative thoracolumbar scoliosis, symptomatic spondylosis and spondylolisthesis.

At baseline, the lumbar spine and SI joint were confirmed as pain generators using physical and clinical exam, imaging studies, and injections as appropriate.

Non-operative management was employed for lumbar spinal pain.

Based on the pain improvement associated with image- guided intra-articular SI joint injection, MIS SI joint fusion was performed without postoperative complications.

After surgery, she continued to have persistent back pain and buttock pain with walking.

Subsequent imaging studies revealed a progression of her scoliotic curve above L3 with pelvic obliquity and clinical exam suggested multiple pain generators including thoracolumbar spine and degenerative joint disease of the hip.


Pelvic and spinal radiographs at the 5-year visit, and comparison to imaging at 1-year, revealed her SI implants to be intact with no signs of loosening, and a progression of spondylosis at levels above L3.

The 5-year pelvic CT scan showed increased bone density along the walls of the implants, suggestive of biological fixation of the implants in bone.

There were no imaging findings to suggest implant failure as explanation for the subject's residual pain.


In addition to her SI joint problems, this patient suffers from multiple pain generators including hip dysfunction secondary to pelvic obliquity and spondylosis associated with degenerative scoliosis.

A review of this case provokes concern that the symptomatology of other pain generators may have overshadowed any potential improvement after SI joint treatment.

Results from a single image guided intra- articular SI joint injection may be vulnerable to misinterpretation in the context of multiple pain generators.

Some patients may benefit from a second injection.

Positive results on the second injection will confirm the SI joint as the primary PG.

However, an equivocal response of less than 75% pain reduction would suggest the SI joint as a secondary PG [30].

No pain improvement rules out the SI and indicates that other PGs in the lumbar spine-SI joint-hip axis need further investigation.


Subject 1013 is a 50-year old female who presented to the clinic post L4-S1 arthrodesis with complex pain syndrome and concomitant chronic conditions requiring multiple medications to manage her pain.

Furthermore, due to her diminished ambulatory capability, she required assistance in performing activities of daily living.

Subject symptoms and findings on physical exam suggested degenerative sacroiliitis.

The SI joint as a pain generator was confirmed by intra-articular SI joint injection.

The subject underwent a single-side SI joint fusion.


She experienced good pain improvement on the operative side, prompting her to undergo diagnostic testing on the contralateral side followed by SI joint fusion.

Postoperatively, she experienced significant improvement in ambulation and capacity for activities of daily living and near complete resolution of her bilateral SI joint pain.

One year later, her degenerative hip joint disease had progressed, resulting in a left-sided total hip replacement.

This subject declined to participate in the imaging component of the study.

The degradation of function and high ODI score at the 5-year assessment seems associated with recurrent spine-related low back pain.


Subject 1002 is a 50-year old female who underwent left SI joint fusion for degenerative sacroiliitis after previous L4- S1 instrumented arthrodesis for degenerative spondylosis and spondylolisthesis.

Postoperatively, she suffered from an infected hematoma secondary to hematogenous seeding from recurrent diverticulitis that resolved after a 6-week course of intravenous antibiotics.

Clinically, the process to control her infection overshadowed her improvement from SI surgery.

Several years after her SI joint fusion, she was diagnosed with L3/4 adjacent segment disease and experienced partial pain relief after L3/4 laminectomy.

At the 5-year visit, there were no imaging findings to suggest implant failure as explanation for the subject's residual pain.

This subject reported symptoms in her contralateral SI joint and continuing symptoms from L3/4 that will likely require arthrodesis.

Therefore, the lumbar pain generators and symptoms from her contralateral SI joint have influenced the degree of her functional improvement after the index procedure.


All 7 patients with the SI joint as the sole PG experienced good to excellent outcomes.

In the 10 patients with multiple PGs, 7 had favorable outcomes while residual pain from secondary PGs eclipsed symptom relief in the remaining 3 patients.

There were no distinguishing characteristics on imaging between responders and non-responders.

Residual symptoms did not correlate with implant failure or lack of boney integration.

Accordingly, no correlation between clinical and radiographic outcomes can be made.


The 5-year results of patients treated for degenerative sacroiliitis and/or SI joint disruptions with MIS SI joint fusion using a series of triangular TPS coated implants presented herein demonstrate the long-term durability of positive outcomes regarding pain relief, return to function, and satisfaction with surgery.

Though pre-operative ODI scores were unavailable for the current case series, the published range for patients with SI joint disorders is 52.6- 61.8 [23, 24, 31].

Our mean 5-year postoperative ODI score (21.5) indicates minimal to moderate impact on functional capacity, and is commensurate with results from other published studies.

Long-term complications of MIS SI joint fusion were rare.

No subject underwent revision of SI joint arthrodesis.

Similar to other reports, a large portion (47%) of patients in the present cohort had a history of previous lumbar spinal fusion.

In contrast to a report describing the use of hollow modular anchorage screws, the degree of pain improvement for patients in the current study was not affected by a history of prior lumbar spinal fusion [19].

As with all studies, we observed variations in patient outcomes.

In the current cohort, the number of pain generators, either single or multiple, influenced patient perception of improvement in pain and function after surgery.

Amongst subjects who did not respond, multiple pain generators (PG) were apparent.

Determination of primary versus secondary pain generators is critical in patients that present with multiple PGs.


Imaging studies at 5 years postoperatively revealed no evidence of implant loosening, confirmed by a consistent observation of increased bone density immediately adjacent to all walls of all implants, suggestive of biological fixation in bone.

The cause of the sclerotic bony margin often observed on the upper wall of the most cranial implant is unknown, but may be the result of a) impaction from broaching step of the procedure, b) micromotion after initial implant placement, or c) as a result of Wolff's law in response to higher loading conditions.

Further investigation is needed to fully understand the mechanism.

After close evaluation of the appearance of the implants on plain film radiographs and CT imaging, we have come to appreciate the difference between lucency along an implant wall and actual loosening of the device.

An observation of apparent linear lucency along the wall, nose or shoulder of the implant on x- ray did not correlate with true lucency on CT in the present study, but rather with an artifact generated by the titanium implant.

In our experience, true loosening of the implant will result in the appearance of an enlarged gap between the implant and a sclerotic margin on both x-ray and CT (Fig. 7).

If implant loosening is suspected, it is vital to correlate clinical symptoms with 3 views on CT to differentiate artifact, lucency and loosening.


Multiple non-surgical and surgical treatments for SI joint disorders are available.

When non-surgical management fails to provide adequate relief of symptoms, surgical arthrodesis is an option.

Published case series of various arthrodesis techniques (both open and MIS) report variable degrees of improvement in pain and function, with more invasive approaches reporting moderately high complications and non-unions [22].

MIS techniques overall report significant improvements in pain and function, but results vary with surgical technique and patient selection.


Positive clinical outcomes are based on accurate diagnosis and assessment of all potential pain generators in the lumbar spine, SI joint and hip.

Correctly diagnosing SI joint disorders requires a rigorous approach to arrive at an accurate diagnosis.

A detailed history, comprehensive physical examination, and an index of suspicion are required to formulate a differential diagnosis.

The practitioner utilizes imaging and diagnostic testing for the process of inclusion/exclusion of the different diagnostic possibilities.


Several pathophysiologic conditions that affect the lumbar spine-SI joint-hip axis can present similarly and typically low back pain patients have multiple pain generators.

Biomechanical studies clearly show an interdependent kinematic relationship within the lumbopelvic hip complex, with changes in one structure affecting degree of motion and load within the entire complex [32].

Therefore, the SI joint should be evaluated as a potential pain generator in patients who fail to improve or experience late non-mechanical failures after lumbar arthrodesis.


Pain and degeneration in the SI joint after lumbar arthrodesis has been reported to range between 43 and 75% [6, 30, 33, 34].

The relatively low success rate of spinal fusion, combined with the high incidence of diagnosable SI joint disorders in patients presenting with low back pain strongly suggests that the SI joint is often overlooked as a PG in this population [3].


An accurate diagnosis requires not only a ruling out or downgrading of other conditions, but also a thorough evaluation of the lumbar spine and hip, as well as a physical exam that includes maneuvers that stress the SI joint and a series of image-guided intra-articular diagnostic injections.


For patients with multiple pain generators, the most bothersome should be treated first to assess the true impact of the secondary pain generator(s).

Surgical treatment of the primary PG alone may effectuate adequate pain control in certain patients, while for others sequential treatment of secondary PGs may be indicated to achieve a satisfactory 382 The Open Orthopaedics Journal, 2014, Volume 8 Rudolf and Capobianco final outcome.

Patients with multiple pain generators, regardless of treatment, may not experience a high degree of improvement as the cortical region of the sensory homunculus governing the low back and hip is relatively small, making it difficult for the brain to distinguish discrete pain generators in this area [35].

Functional improvement relies on the interdependent relationship of the lumbar spine, pelvis and hip axis.

Pain or loss of function in one component can overshadow improvement in another.

Identification and sequential treatment of secondary pain generators in this axis may be needed to achieve the best possible outcome.


Although the study sample size is relatively small and represents the experience of a single surgeon, this cohort represents the first patients to have received this implant.

ODI was available only at the 5-year time point; a comparison to baseline could not be performed.

It should be noted, however, that all pain and functional outcomes were self-reported by study subjects.

Larger cohort and multi- center long-term studies are needed to better understand how to formulate a surgical strategy and set realistic outcome expectations in the patient with multiple pain generators within the lumbar spine-SI joint-hip axis.


Long-term (5-year) clinical and radiographic outcomes after MIS SIJ fusion for degenerative sacroiliitis and/or SI joint disruptions are favorable.

Clinical improvements observed at 12 months postoperatively were maintained at 5years.

There was no evidence of long-term complications, implant migration or loosening.

Increased bone density was observed circumferentially in 100% of the implants.

Most (87%) scans showed intra-articular osseous bridging.

Patients who did not do well were affected by multiple severe degenerative conditions of the spine, pelvis, and/or hip.


LR is an SI-BONE, Inc. investor, consultant and clinical trial investigator.

RC is an SI-BONE, Inc. employee.


The sacroiliac joint (SIJ) may be a source of chronic low back pain in 15-22% of patients.


Over the past four years, minimally invasive surgery (MIS) has become an emerging standard of care for SI joint fusion.


The International Society for the Advancement of Spine Surgery (ISASS) and Society for Minimally Invasive Spine Surgery (SMISS) conducted a survey of their members to examine current preferences in surgeon practice of MIS SI fusion.


To qualify for survey participation, the surgeon had to perform at least one open or MIS SIJ fusion procedure between 2009 and 2012.


All surgeons were instructed to review their records.


This included the number of surgical procedures performed annually from 2009-2012, site of service where each procedure was commonly performed, and average length of stay for each approach.


Twenty-four percent (121/500) of the eligible members participated in this survey.


This survey revealed that the percentage of MIS procedures increased from 39% in 2009 to over 87% in 2012.


The survey showed a significant increase in the average number of MIS surgeries and a significant difference between open and MIS surgeries in 2012 (p<0.0001).


In addition, 80% of the survey respondents indicated a lack of preference toward the open approach if that was the only available option.


According to the performed survey, MIS SIJ fusion is preferred over the open technique.


Incorporation of the MIS technique into the spine surgeon's spectrum of skills would allow an increased number of surgical options as well as a possible increase in outcome quality.


Sacroiliac joint dysfunction, caused by degenerative sacroiliitis or sacroiliac disruption, has been recognized as a legitimate pain generator since the 1800s, but has remained under-appreciated and under-treated until the emergence of advanced diagnostic methods as well as the development of reasonable, effective, and less morbid interventional modalities.


Sacroiliac Joint (SI joint) pain is a significant cause of low back pain [1-3].


It has been reported as the pain generator in 15%-22% of patients with low back pain [1,4].


Non-operative management such as physical or manual therapy and fluoroscopic guided steroid injections are the first line treatment and in many cases the definitive treatment [4-6].


When non-operative management fails and SI joint symptoms persist, arthrodesis becomes a viable option.


A variety of surgical techniques have been developed to fuse the SI joint, including traditional open arthrodesis with plates and/or screws.


Emerging minimally invasive techniques have been developed because of potential advantages such as minimizing soft-tissue trauma, less operative blood loss, faster rehabilitation, and reduced length of hospital stay [7-9, 11, 13, 14].


Surgeons should choose the approach that will provide the best clinical outcome for the patient and treat their medical condition with the least risk of complications.


Since the development of instrumentation allowing SI joint fusions via a less invasive approach, the number of open procedures has significantly declined because the surgeon community appears to prefer the minimally invasive approach in the best interest of their patients [18].


Over the past four years, MIS is an emerging standard of care for SI joint fusion.


The International Society for the Advancement of Spine Surgery (ISASS) and Society for Minimally Invasive Spine Surgery (SMISS) conducted a survey of their members to examine current preferences in surgeon practice of MIS SI fusion.


Previous reports of minimally invasive (MIS) sacroiliac (SI) joint fusion for low back, SI joint, and buttock pain secondary to SI joint disorders have shown favorable short- and mid-term outcomes.

Herein we present 5-year clinical and radiographic outcomes after MIS SI joint fusion using a series of triangular porous titanium plasma spray (TPS) coated implants.

Consecutive patients treated with MIS SI joint fusion for degenerative sacroiliitis and/or sacroiliac joint disruptions between October 2007 and March 2009 were evaluated.

Pain on VAS, an SI joint specific survey and Oswestry Disability Index (ODI) were administered.

X-ray and CT scans were obtained to assess the implants.

Of 21 patients treated, 17 were available for the study.

Mean age was 58 years (range 36-85), 77% were female and 47% had prior lumbar spinal fusion.

Pain on VAS improved from 8.3 at baseline to 2.4 at 5 years; 88% of patients reached Substantial Clinical Benefit.

Mean ODI score at 5 years was 21.5 (SD 22.7).

Patient satisfaction achieved at 12 months was maintained for 5 years (82%).

A qualitative review of x-ray and CT imaging showed increased bone density immediately adjacent to all implants, intra-articular osseous bridging in 87% of patients and no evidence of implant loosening or migration.

Long-term clinical and radiographic outcomes after MIS SIJ fusion are favorable.

Clinical improvements observed at 12 months postoperatively were maintained at 5 years.

There was no evidence of long-term complications, implant loosening or migration.

Patients who did not achieve large improvements were affected by multiple severe concomitant degenerative conditions of the lumbar spine, pelvis, and/or hip.


Chronic lower back pain is well known as a public health epidemic.

In highly developed countries, it is one of the top 3 causes of degradation in quality adjusted life years, along with ischemic heart disease and chronic obstructive pulmonary disease [1].

While lumbar spine pathology is an important cause of chronic lower back pain, substantial evidence suggests that not all low back pain is due to lumbar spine pathology.

The SI joint is thought to be the source of pain in up to 30% of patients evaluated for chronic lower back pain [2-5].

Disorders of the SI joint may be the result of trauma, pregnancy, inflammatory arthritis, osteoarthritis or degeneration of the joint either de novo or after lumbar spinal fusion [6].

In the case of lumbar spinal arthrodesis, sacroiliac joint pathology may explain delayed postoperative pain or a failure for the patient to experience symptom improvement in the early postoperative period (failed back surgery syndrome) [7, 8].

Diagnosing the SI joint as the primary or sole pain generator (PG) can be complex as patients often present with a combination of low back, groin, gluteal, and/or leg pain and the symptom profile may mimic other disorders of the lumbar spine and hip [2, 9].

Additionally, some patients present with more than one pain generator within the lumbar spine-SI joint-hip axis, making the identification of the primary versus secondary pain generators more challenging [3].

Furthermore, SI joint imaging studies are typically neither sensitive nor specific to abnormalities in the absence of trauma, tumor, ankylosing spondylitis, or infection [10].

SI joint pain can be debilitating and treatment with non-operative care is often unsuccessful.

The impact of pain on persons living with the disease is similar to that associated with other prominent orthopedic conditions routinely treated surgically [11].

Furthermore, the economic burden of non-operative care is significant for Medicare as well as commercial payer entities with a 5-year estimated cost of $270 million for Medicare beneficiaries and a 3-year estimated cost of $1.6 billion per 100,000 commercial covered lives [12, 13].

Surgical treatment options for SI joint disorders have been unattractive until relatively recently.

Open arthrodesis, commonly performed throughout the 1900s, is now reserved primarily for traumatic pelvic ring fractures due to the invasiveness of the procedure, coupled with a high morbidity rate [14-16].

In recent years, several minimally invasive techniques for fusing the SI joint have been introduced into the surgical repertoire [17-21].

MIS SI joint fusion for certain SI joint disorders (degenerative sacroiliitis and SI joint disruptions), specifically using a series of triangular titanium implants, has been shown to result in lower morbidity, including shorter operating times and hospital stays, fewer complications, a lower reoperation rate, and higher gains in patient quality of life compared to the open surgical method, as evidenced by a recent comparative cohort study [22].

The current body of medical literature substantiates positive short to mid-term clinical outcomes [17, 23-25].

However, no long-term clinical or radiographic outcomes have been published to date.

Herein we report 5-year clinical effectiveness, safety and radiographic outcomes in patients treated with MIS SI joint fusion for degenerative sacroiliitis or sacroiliac joint disruptions using a series of triangular, porous titanium plasma spray (TPS) coated implants (iFuse Implant System®, SI-BONE, Inc., San Jose, CA) from a single center.


All consecutive patients who underwent MIS SI joint fusion between October 2007 and March 2009 at a single center were identified.

Prior to surgery, all patients were diagnosed with either degenerative sacroiliitis and/or SI joint disruptions using a detailed history, combination of physical provocative maneuvers specific to the SI joint, image-guided intra-articular SI joint injections and various imaging modalities [17].

MIS SI joint fusion was performed in all patients by placing a series of implants laterally across the SI joint, as previously described [17, 23].

Patients were contacted and asked to participate in a long-term evaluation, which included a clinical exam as well as an optional radiographic imaging component.

Patients signed a study-specific, IRB-approved consent form before beginning any study-related activity.

Patients were asked to reveal and discuss any further surgical treatment they received for SI joint, lumbar spine, pelvic or hip disorders.

A series of patient reported outcome instruments, described below, was also administered.

Participants who resided outside of a reasonable travel distance were given the opportunity to provide responses by phone or mail.

Patients who consented to the radiographic component of the study had both plain film radiographs (outlet and anteroposterior (AP) views) and computed tomography (CT) scans of the pelvis.

These imaging tests were used to assess implant position, evidence of lucency adjacent to the implant, qualitative increase in bone density adjacent to the implant, and presence of intra-articular osseous bridging.

The 5-year images were compared to those previously acquired closest to the one-year follow-up interval.

Data extracted from the medical charts included demographics, diagnosed pain generators in the lumbar spine-SI joint-hip axis, pain treatments received, perioperative measures, adverse events, one-year imaging studies, and previously administered patient reported outcomes at 12- and 24-months postoperatively, described below.


Pain and functional outcomes were assessed in a prospective manner pre-operatively and at 12-, 24- and 60-months postoperatively.

Level of pain was assessed using a 0-10 visual analog scale (VAS).

Prior to the initial experience with the surgical procedure, a 9-question SI joint-related health outcomes survey was created with response domains taken from both the SF-36 and Oswestry Disability Index (ODI) (Fig. 1): pain level, the ability to perform light, moderate and vigorous activities, quality of sleep, lifting ability, happiness, social activities, and the effect of pain on social life [17].

A numerical rating scale of 0-10 with 0 representing no pain or difficulty and 10 representing the worst pain imaginable or severe difficulty was used for all domains.

Satisfaction with surgery was assessed in a binary fashion (yes or no) by asking if the patient would have the same surgery again for the same result.

The SI joint-related health outcomes survey and VAS were administered preoperatively and at 12- and 60-months postoperatively.

At 24 months, patients were contacted to assess SI joint pain on VAS.

The ODI was administered at the 60-month visit only.

Satisfaction and safety events were collected at all postoperative time points.

Demographic variables were tabulated and expressed as frequency and means with standard deviation, where appropriate.

A repeated measures analysis of variance (ANOVA) was used to compare VAS pain scores from baseline to all postoperative time points.

A paired t-test was used to assess improvement from baseline to the 60-month time point on the SI joint survey.

An unpaired t-test was performed to assess the effect of sex and history of prior lumbar spinal fusion on outcomes.

Statistical analyses were performed using R software [26].

Clinical improvement was defined using previously validated minimum clinically important difference (MCID) and substantial clinical benefit (SCB) values for back pain on VAS.

MCID is defined as a change of >2.0 points and SCB is defined as a 2.5-point decrease or a raw score of < 3.5 [27, 28].

Institutional Review Board approval was obtained before beginning this study.


Of 21 consecutive patients who underwent MIS SI joint fusion, 17 were available for follow-up and form the analysis cohort.

Of those not available, 2 had died unrelated to spine conditions, one was lost to follow-up and one suffered a severe neck trauma rendering the patient quadriplegic and unable to provide relevant data.

All available patients participated in the clinical portion of the study and 15 of 17 (88%) agreed to participate in the radiographic component.

Mean subject age was 58 (±14) years (range 36-85), 77% were female and 47% had undergone lumbar spinal fusion prior to SI joint fusion (Table 1).

Slightly more subjects had the right SI joint treated (53%) compared to the left (41%), and one patient underwent bilateral treatment.

Mean operating time was 65 (±18) minutes, range (43-110).

There were no intraoperative complications.

Postoperative events, which primarily included hematoma (1), cellulitis (2), and deep infection secondary to diverticulitis (1), were previously reported in detail [17].

Improvement in pain was clinically and statistically significant at all follow-up intervals compared to baseline (all p<0.001) (Table 2).

All subjects who reached MCID also reached SCB.

The percentage of patients who achieved both MCID and SCB remained high at each time point (77%, 82%, and 88% at 12-, 24- and 60-month visits, respectively).

No statistical effect was found for sex, or history of lumbar fusion on pain improvement at any time point.

At 60-months, statistically significant improvement was seen in 6 of 8 domains of the SI joint survey instrument (Table 3): the ability to perform light, moderate and vigorous activities, sleep disturbance caused by pain, overall happiness, and the effect of pain on social life.

The ability to perform light, moderate and vigorous activities showed continual improvement from 12 months to the 5-year time interval.

Patient satisfaction scores obtained at the 12-month interval were unchanged at 2- and 5-years postoperatively; 82% (14/17) would have the same surgery again for the same result at all time points.

ODI scores were obtained at the 5-year follow-up only (Table 4).

Mean (SD) ODI score was 21.5 (22.7).

Fairbank categorized scores in terms of degree of disability, with 0-20 representing minimal disability and 21-40 representing moderate disability requiring conservative care only [29].

Results show the majority (71%) of subjects are living with minimal or moderate disability.


Pelvic AP and outlet view plain films radiographs and a pelvic computed tomography (CT) scan were performed on 15 subjects; 45 implants were assessed.

Imaging studies obtained at 5 years were compared to available studies acquired as close as possible to the one-year postoperative time point.

A qualitative comparison of 1- and 5-year pelvic plain film radiographs, including AP and outlet views, revealed no change in implant position (Fig. 2).

CT scans of the pelvis with axial, sagittal, and coronal reconstructions documented increased bone density circumferentially along three implant walls for all implants on both the iliac and sacral segments.

Evidence of osseous bridging across the SI joint was clearly seen on 13 of 15 (87%) of patients (Fig. 3).

On x-ray, what appeared to be full-length lucency (absence of bone adjacent to an implant) along the wall of the implant was consistently observed on at least one implant in all patients on AP view.

However, this observation was not evident on the outlet view.

Upon review of CT imaging, this apparent lucency was confirmed to be an artifact (Fig. 4).

Assessment and comparison of CT scans at 1- and 5-years revealed a consistent pattern of artifacts at the corners and periodically along the wall of an implant, which were non-progressive and unchanged in equivalent projections on the axial, sagittal and coronal sections.

A small area of true focal lucency was observed on CT scans in 4 patients; along the superior edge of the most cranial implant on the iliac side in 3 patients, and on the superior edge of the most caudal implant on the iliac side in one patient (Fig. 5).

Other findings included a regular pattern of sclerotic bone response at the implant entry point in the ilium, on primarily the superior implant (Fig. 6).

A detailed explanation of the physics of CT imaging of triangular titanium implants is outside the scope of this manuscript and will be reported separately.


Three subjects in the current cohort did not improve satisfactorily.

To understand why these patients failed to improve and to refine patient selection criteria for MIS SI joint fusion, an in-depth interview was performed for each patient.

Patient vignettes are described below.

Subject 1012 is a 72-year old woman who presented to the clinic complaining of low back and pelvic pain.

The subject’s history included a successful total knee replacement as well as L3-L5 arthrodesis for degenerative thoracolumbar scoliosis, symptomatic spondylosis and spondylolisthesis.

At baseline, the lumbar spine and SI joint were confirmed as pain generators using physical and clinical exam, imaging studies, and injections as appropriate.

Non-operative management was employed for lumbar spinal pain.

Based on the pain improvement associated with image-guided intra-articular SI joint injection, MIS SI joint fusion was performed without postoperative complications.

After surgery, she continued to have persistent back pain and buttock pain with walking.

Subsequent imaging studies revealed a progression of her scoliotic curve above L3 with pelvic obliquity and clinical exam suggested multiple pain generators including thoracolumbar spine and degenerative joint disease of the hip.

Pelvic and spinal radiographs at the 5-year visit, and comparison to imaging at 1-year, revealed her SI implants to be intact with no signs of loosening, and a progression of spondylosis at levels above L3.

The 5-year pelvic CT scan showed increased bone density along the walls of the implants, suggestive of biological fixation of the implants in bone.

There were no imaging findings to suggest implant failure as explanation for the subject’s residual pain.

In addition to her SI joint problems, this patient suffers from multiple pain generators including hip dysfunction secondary to pelvic obliquity and spondylosis associated with degenerative scoliosis.

A review of this case provokes concern that the symptomatology of other pain generators may have overshadowed any potential improvement after SI joint treatment.

Results from a single image guided intra-articular SI joint injection may be vulnerable to misinterpretation in the context of multiple pain generators.

Some patients may benefit from a second injection.

Positive results on the second injection will confirm the SI joint as the primary PG.

However, an equivocal response of less than 75% pain reduction would suggest the SI joint as a secondary PG [30].

No pain improvement rules out the SI and indicates that other PGs in the lumbar spine-SI joint-hip axis need further investigation.


Subject 1013 is a 50-year old female who presented to the clinic post L4-S1 arthrodesis with complex pain syndrome and concomitant chronic conditions requiring multiple medications to manage her pain.

Furthermore, due to her diminished ambulatory capability, she required assistance in performing activities of daily living.

Subject symptoms and findings on physical exam suggested degenerative sacroiliitis.

The SI joint as a pain generator was confirmed by intra-articular SI joint injection.

The subject underwent a single-side SI joint fusion.

She experienced good pain improvement on the operative side, prompting her to undergo diagnostic testing on the contralateral side followed by SI joint fusion.

Postoperatively, she experienced significant improvement in ambulation and capacity for activities of daily living and near complete resolution of her bilateral SI joint pain.

One year later, her degenerative hip joint disease had progressed, resulting in a left-sided total hip replacement.

This subject declined to participate in the imaging component of the study.

The degradation of function and high ODI score at the 5-year assessment seems associated with recurrent spine-related low back pain.


Subject 1002 is a 50-year old female who underwent left SI joint fusion for degenerative sacroiliitis after previous L4-S1 instrumented arthrodesis for degenerative spondylosis and spondylolisthesis.

Postoperatively, she suffered from an infected hematoma secondary to hematogenous seeding from recurrent diverticulitis that resolved after a 6-week course of intravenous antibiotics.

Clinically, the process to control her infection overshadowed her improvement from SI surgery.

Several years after her SI joint fusion, she was diagnosed with L3/4 adjacent segment disease and experienced partial pain relief after L3/4 laminectomy.

At the 5-year visit, there were no imaging findings to suggest implant failure as explanation for the subject’s residual pain.

This subject reported symptoms in her contralateral SI joint and continuing symptoms from L3/4 that will likely require arthrodesis.

Therefore, the lumbar pain generators and symptoms from her contralateral SI joint have influenced the degree of her functional improvement after the index procedure.


All 7 patients with the SI joint as the sole PG experienced good to excellent outcomes.

In the 10 patients with multiple PGs, 7 had favorable outcomes while residual pain from secondary PGs eclipsed symptom relief in the remaining 3 patients.

There were no distinguishing characteristics on imaging between responders and non-responders.

Residual symptoms did not correlate with implant failure or lack of boney integration.

Accordingly, no correlation between clinical and radiographic outcomes can be made.