In recent years, lumbar spinal fusion has become common

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1 SPINE Volume 41, Number 12, pp ß 2016 Wolters Kluwer Health, Inc. All rights reserved CLINICAL CASE SERIES Fusion of Multiple Segments Can Increase the Incidence of Sacroiliac Joint Pain After Lumbar or Lumbosacral Fusion Eiki Unoki, MD, Eiji Abe, MD, Hajime Murai, MD, Takashi Kobayashi, MD, and Toshiki Abe, MD Study Design. A retrospective study. Objective. To determine the risk factors for sacroiliac joint pain (SIJP) after lumbar or lumbosacral fusion. Summary of Background Data. Recently, the sacroiliac joint has gained increased attention as a source of pain after lumbar or lumbosacral fusion. We examined the factors related to the development of SIJP after lumbar or lumbosacral fusion. Methods. In total, 262 patients who underwent lumbar or lumbosacral fusion from June 2006 to June 2009 were included in this study. All patients who did not show SIJP clinically in the preoperative screening period were considered. Of these patients, 28 newly developed SIJP. We investigated whether development of SIJP after lumbar or lumbosacral fusion is related to the presence of fusion involving the sacrum (floating fusion vs. fixed fusion) and the number of fused segments. Results. The incidence of SIJP was higher with fixed fusion (13.1%) than with floating fusion (10.0%). With regard to the number of fused segments, the incidence of SIJP was 5.8% for one fused segment, 10.0% for two segments, 20.0% for three segments, 22.5% for at least four segments. Thus, the incidence was significantly higher when at least three segments were fused. Logistic regression analysis was performed to determine if the development of SIJP was related to the presence of fusion involving the sacrum or the number of fused segments. The analysis revealed that the number of fused segments was significantly associated with the development of SIJP. Conclusion. SIJP is a potential cause of low back pain after lumbar or lumbosacral fusion surgeries. Our study indicated that fusion of multiple segments (at least three) can increase the incidence of SIJP after lumbar or lumbosacral fusion. Key words: lumbar fusion, lumbosacral fusion, sacroiliac joint pain. Level of Evidence: Level 3 Spine 2016;41: In recent years, lumbar spinal fusion has become common in the treatment of various lumbar disorders. 1 However, despite careful selection of patients, the failure rate ranges from 5% to 30% according to previous studies. 2,3 It is common for low back pain (LBP) to persist postoperatively or develop newly, and treating this pain can be difficult. The potential explanations for LBP after lumbar fusion include iliac graft harvesting, 4 adjacent segment disease (ASD), 5 pseudarthrosis, sacroiliac joint pain (SIJP), 6 or fusion hardware-related LBP. 4,7 Since the 2000s, several authors have suggested that SIJP can cause LBP after lumbar fusion. 3,7 9 We conducted a retrospective study of the primary causes of SIJP after lumbar fusion by investigating the relationship of SIJP with the presence of fusion involving the sacrum and with the number of fused segments. MATERIALS AND METHODS From the Department of Orthopedic Surgery, Akita Kousei Medical Center, Nishifukuro, Akita, Japan. Acknowledgment date: June 24, First revision date: December 14, Acceptance date: December 14, The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No relevant financial activities outside the submitted work. Address correspondence and reprint to Eiki Unoki, MD, Department of Orthopedic Surgery, Akita Kousei Medical Center, Iijima, Nishifukuro, Akita , Japan; e.unoki.a.r.h.orthop@ .plala.or.jp Patients Between June 2006 and June 2009, 302 patients underwent lumbar fusion. All patients who did not show SIJP clinically in the preoperative screening period were considered. All patients involved posterior spinal instrumentation surgery without iliac graft harvesting. Two patients were excluded because of preoperative LBP that persisted postoperatively; we thought that the contribution of the mental factor due to pain could not be denied because the cause of their pain could not be clarified from objective findings. Of the remaining 300 patients, 262 were able to undergo follow-up for >2 years after surgery (follow-up rate: 87.3%), and 38 could not undergo follow-up. Thus, 262 patients were included in the study. The mean DOI: /BRS Spine 999

2 TABLE 1. Patient Demographics Follow-Up (2 Yr) Group (n ¼ 262) Lost to Follow-Up (<2 Yr) Group (n ¼ 38) Follow-Up Period (Mo), Mean (Range) (24 100) (1 21) Age (yr), mean (range) (20 86) (27 86) P ¼ Sex Male (%) 100 (38.2) 20 (52.6) Female (%) 162 (61.8) 18 (47.4) P ¼ No. of fused segments One segment (%) 137 (52.3) 22 (57.9) Two segments (%) 60 (22.9) 12 (31.5) Three segments (%) 25 (9.5) 1 (2.6) At least four segments (%) 40 (15.3) 3 (7.9) Mean number of fused P ¼ segments Lower fused level Not sacrum (%) 201 (76.7) 30 (78.9) Sacrum (%) 61 (23.3) 8 (21.1) P ¼ Preoperative diagnosis Degenerative lumbar spondylolisthesis Lumbar spinal canal stenosis 41 1 Degenerative lumbar kyphosis 29 3 Lumbar disc herniation 24 2 Degenerative lumbar 21 1 kyphoscoliosis Degenerative lumbar scoliosis 19 2 Spondylolytic 14 5 spondylolisthesis Osteoporotic kyphosis 14 3 Lumbar foraminal stenosis 9 1 Discal cyst 7 1 x 2 test for sex and lower fused level. Student t test for age and mean number of fused segments. number of fused segments was Furthermore, floating fusion (sacrum not fused) was performed in 201 patients and fixed fusion (sacrum fused) was performed in 61 patients. Exclusion of the 38 patients who werelosttofollow-up didnot significantly affect the results related to the test items, that is, mean number of fused segments and presence or absence of fusion involving the sacrum. The demographics of the patients are shown in Table 1. Investigation For all patients, postoperative follow-up was performed by spine surgeons (EA, HM, TK, and TA). Patients in whom LBP developed newly after surgery were extracted by thorough investigation of the medical records. The cause of LBP after surgery was diagnosed by physical, neurological, and imaging findings. If needed, additional nerve root block, facet block, and lumbar discography were performed. In the likelihood that the pain was caused by instruments, a local anesthetic was injected into the pain site. Patients with suspected SIJP in whom lumbar-derived causes were ruled out were all referred to the main author (EU) (the main author was responsible for SIJP at our hospital). Then, the main author re-examined the patients and administered a sacroiliac joint (SIJ) block. The SIJ block was performed under fluoroscopic guidance, with 2 ml of 2% lidocaine injected into SIJ. Pain relief in each patient was evaluated using a visual analog scale, and scores obtained before and within 15 to 45 minutes after the SIJ block were compared. Diagnostic Criteria for SIJP In accordance with the diagnostic criteria of Murakami et al, 10 patients who met the following conditions were diagnosed with SIJP. A. Pain located unilaterally in the lower lumbar region and buttocks. B. Pain not caused by other diseases of the lumbar spine. C. Positive findings on at least two provocation tests (Patrick test, Gaenslen test, and SIJ shear test). D. Pain relief of 70% achieved by SIJ block June 2016

3 TABLE 2. Characteristics of Patients With SIJP After Fusion Surgery (N ¼ 28) Pain-Free Age/ Preoperative Range of Interval Preoperative Postoperative Sex Diagnosis Fused Segments (Mo) Symptoms Symptoms 78F DLS L2 5 3 LBP, Lt. leg numbness Lt. LBP 76F DLS L2 S1 3 LBP, Lt. leg pain Rt. LBP 74F DLS L LBP, Bt. leg numbness Lt. LBP 73F DLS L3 5 2 LBP, Bt. leg numbness Lt. LBP 61F DLS L2 5 8 LBP, Lt. leg pain, Rt. LBP Rt. leg numbness 76F DLKS L3 S1 2 LBP, Lt. leg pain Lt. LBP 74F DLKS L LBP, Bt. leg numbness Lt. LBP 73F DLKS L1 S1 3 LBP, Bt. leg numbness Rt. LBP 72M DLKS L2 S1 6 LBP, Lt. leg pain Rt. LBP, Rt. leg pain 80F DLK T12 S1 1 LBP, Rt. leg pain, numbness Rt. LBP, Rt. leg pain, numbness 77M DLK L1 S1 1 LBP, Bt. leg pain, numbness Rt. LBP, Rt. leg pain 75F DLK L2 5 8 LBP Rt. LBP 67F Osteoporotic kyphosis T9 L3 10 LBP Lt. LBP 64F Osteoporotic kyphosis T10 L2 3 LBP, Bt. leg numbness Rt. LBP 74F Foraminal stenosis L Lt. LBP, Lt. leg pain Lt. LBP 73F Foraminal stenosis L4 S1 2 Lt. leg pain Lt. LBP, Lt. leg numbness 73F Foraminal stenosis L4 5 9 LBP, Lt. leg pain Lt. LBP 66M Foraminal stenosis L4 S1 3 LBP, Bt. leg pain Lt. LBP 72F Spondylolisthesis L4 5 5 LBP, Lt. leg pain Rt. LBP 71F Spondylolisthesis L4 5 7 LBP Rt. LBP 67F Spondylolisthesis L Bt. leg numbness Rt. LBP 59F Spondylolisthesis L3 5 4 LBP Lt. LBP 59F Spondylolisthesis L3 5 3 Lt. leg pain Lt. LBP, Lt. leg numbness 79M LSCS L LBP, Lt. leg pain, numbness Rt. LBP 77F LSCS L4 5 3 Bt. leg numbness Rt. LBP 74F LSCS L3 4 8 Bt. leg numbness Rt. LBP, Rt. leg pain 67F LDH L4 5 3 Lt. leg pain Lt. LBP 48F Discal cyst L LBP, Rt. leg pain Lt. LBP Bt indicates bilateral; DLK, degenerative lumbar kyphosis; DLKS, degenerative lumbar kyphoscoliosis; DLS, degenerative lumbar scoliosis; LBP, low back pain; LDH, lumbar disc herniation; LSCS, lumbar spinal canal stenosis; Lt, left; Rt, right; SIJP, sacroiliac joint pain. Evaluation The following parameters were evaluated: Proportion of patients with SIJP among those with LBP who developed postoperatively. Characteristics of SIJP after fusion surgery. Difference in the rate of onset of SIJP between floating fusion and fixed fusion. Incidence of SIJP according to the number of fused segments, that is, one segment, two segments, three segments, and at least four segments. Risk factors for the onset of SIJP, including the number of fused segments and fusion involving the sacrum, were analyzed by multivariate analysis to determine which factor was more greatly involved. Statistical Analysis Statistical analysis was performed using Statview 5.0 version software (Abacus Concepts, Berkeley, CA). Dichotomous data were compared using Student t test and x 2 test. Logistic regression analysis was used for analyzing the risk factors for the onset of SIJP. In this analysis, the explanatory variables were fusion involving the sacrum and number of fused segments. The response variable was SIJP. A P value of <0.05 was considered significant. RESULTS All 262 patients showed an amelioration of preoperative symptoms. However, 66 patients newly developed LBP during the postoperative follow-up period. Of these 66 patients, SIJP was diagnosed in 28 (42.4%) patients. Furthermore, symptomatic ASD, proximal junctional fracture, instrument-related LBP, and pseudarthrosis were observed in 23 (34.8%), 8 (12.1%), 5 (7.6%), and 2 (3.0%) patients, respectively. Table 2 shows the characteristics of the 28 patients diagnosed with SIJP. They included four men and 24 women aged 48 to 80 years (mean age, 70.7 yr). The postoperative Spine

4 Upon comparing the incidence of SIJP and the number of fused segments, SIJP occurred in eight (5.8%) of the 137 patients with one fused segment, six (10.0%) of the 60 patients with two fused segments, five (20.0%) of the 25 patients with three fused segments, and nine (22.5%) of the 40 patients with at least four fused segments. The incidence of SIJP increased with the number of fused segments, and SIJP was significantly more common in patients with at least three fused segments (Table 4). The number of fused segments and presence of fusion involving the sacrum were analyzed by logistic regression analysis to determine which contributed more to the onset of SIJP. The result indicated that the number of fused segments had a significant impact (P ¼ ) (Table 5). Figure 1. Fusion levels of 28 patients with sacroiliac joint pain after lumbar/lumbosacral fusion: fusion of one segment, eight patients; two segments, six patients; three segments, five patients; and at least four segments, nine patients. Floating fusion, 20 patients; fixed fusion, eight patients. observation period ranged from 24 to 100 months (mean, 55.2 months). The preoperative symptoms of these 28 patients included LBP alone in four patients, LBP and leg pain or numbness in 18 patients, and leg symptoms alone in six patients. Of the 28 patients with newly developed symptoms postoperatively, 22 exhibited either left or right LBP below the level of L5 and six complained of leg pain and/or numbness in addition to either left or right LBP. The postoperative symptoms differed from the preoperative symptoms in all cases. Preoperative LBP was noted to be midline or symmetrical pain in 21 patients, and one patient had left LBP that included the region above L5. However, postoperative LBP in these 28 patients was observed to be unilateral and in the SIJ region, unlike preoperative LBP. The period from fusion surgery until SIJP onset ranged from 1 to 19 months (mean, 6.6 months). The range of fusion for each patient is shown in Figure 1. Comparison of the incidence of SIJP between fixed fusion and floating fusion indicated that SIJP occurred in eight (13.1%) of the 61 patients who underwent fixed fusion and 20 (10.0%) of the 201 patients who underwent floating fusion. Although the incidence of SIJP tended to be higher with fixed fusion, no significant difference was observed (Table 3). DISCUSSION SIJP accounts for 15% to 25% of LBP; however, it is difficult to diagnose because there are no established clinical, physical, or imaging findings. 11 Various pain provocation tests of SIJ, such as Patrick test and Gaenslen test, are known to help with diagnosis. 12,13 However, when such tests are applied, it is almost impossible to clarify the structure on which the stress is actually placed. 14 Dreyfuss et al 15 reported the sensitivity and specificity for a number of tests, with values of 69% and 16% reported for Patrick test and 71% and 26% for Gaenslen test, respectively. In two recent studies, Laslett et al 16 reported that in the event of at least three positive pain provocation tests, the sensitivity of SIJP diagnosis was 94% and specificity was 78%. Furthermore, van der Wurff et al 17 reported that the sensitivity and specificity of SIJP diagnosis was 85% and 79%, respectively. However, in our study, we used at least two positive provocation tests as the criteria to diagnose SIJP. According to Laslett et al, 16 with at least two positive provocation tests, diagnosis has a sensitivity of 93% and specificity of 66%. The sensitivity is almost comparable. Although the specificity is slightly inferior, we believe that diagnostic accuracy may be improved by combining provocation tests with SIJPspecific physical findings such as pain below the L5 level 15 and in the posterior superior iliac spine region 18,19 and by eliminating other diseases of the lumbar spine. 3 It is difficult to diagnose SIJP on the basis of imaging. In several studies, radiography, computed tomography, and magnetic resonance imaging (MRI) have been used to identify SIJP. However, no reports have indicated a constant TABLE 3. Development of SIJP After Lumbar/Lumbosacral Fusion: Floating Fusion Versus Fixed Fusion Fusion Level No. of Patients Incidence SIJP Incidence Rate Floating fusion (sacrum was not % fused) Fixed fusion (sacrum was fused) % x 2 test for independence, P ¼ , not significant. SIJP indicates sacroiliac joint pain June 2016

5 TABLE 4. Development of SIJP After Lumbar/Lumbosacral Fusion: Number of Fused Segments No. of Fused Segments No. of Patients Incidence SIJP Incidence Rate One segment % Two segments % * Three segments % * At least four segments % x 2 test for independence. P SIJP indicates sacroiliac joint pain. correlation between SIJP diagnosis by imaging findings and by an SIJ block. 20 Given that it is difficult to determine whether pain has originated in SIJ or not on the basis of physical and imaging findings, the SIJ block is considered the gold standard for diagnosis. 3,11 A single block or a double block 14 can be used. In previous studies on SIJP after lumbar fusion, Katz et al, 8 Maigne and Planchon, 3 and DePalma et al 7 used a single block. Similarly, we also report the use of a single block. Liliang et al 9 used a double block because there is a high rate of false-positive results with the single block method. However, this does not mean that there is no possibility of falsepositive results with the double block method. 20 Cohen 11 noted that in actual clinical practice, a double block is rarely used because of the following: (a) the block itself is considered to be definitive treatment; (b) double blocks are not cost-effective; and (c) the negative consequence of obtaining a false false-positive block outweighs the ramifications of overdiagnosing the condition. Although it is widely known that pain from iliac graft harvesting and ASD can cause LBP after lumbar fusion, 4,5 it is not common knowledge that the pain can originate from SIJ (without damage from bone harvesting). However, in recent years, several studies have indicated that it is not rare for postoperative LBP to originate from SIJ. 3,7 9,21 The incidence of SIJP in patients with LBP after lumbar fusion has been reported to be 16.2% to 43% according to previous studies. 3,7 9 In our study, the incidence was 42.4%, which is nearly as high as that reported by DePalma et al 7 (43%). However, our postoperative observation period ranged from 24 to 100 months (mean, 48.5 months), and it is possible that a longer observation period is associated with a higher percentage of ASD and proximal junctional kyphosis. Regarding the mechanism of onset of SIJP after lumbar fusion, Frymoyer et al 6 hypothesized that spinal fusion including the sacrum results in long-term compensatory hypermobility of SIJ and accelerated degeneration of these joints. Katz et al 8 reported that in patients with LBP after lumbosacral fusion, SIJ was the cause of pain in 32% patients and possibly the cause in 29% patients. Maigne et al 3 observed that among patients with SIJP after fusion surgery, 42% had L5 S1 fusion. Thus, they favored Frymoyer hypothesis. Furthermore, they thought that the mechanism of onset of SIJP after lumbar fusion was similar to that of ASD after spinal fusion. Numerous clinical and experimental studies of ASD after lumbar fusion procedures have demonstrated increased mobility in the adjacent cephalad and/or caudal segments and increased stress on the facet and/or disc of adjacent mobile segments The mechanical load transfer would be caused by the straightening of the fused segments. This process is known to cause increased load transfer on the disc above the fusion, 34 and the disc below the fused level is subjected to new strains 35 associated with a transitional (shear) motion 36 that may result in pain. In the case of lumbosacral fusion, SIJ is the joint adjacent to the fused segment, and similar biomechanical responses could apply to SIJ. 3,8,37,38 In a previous study, Ha et al 37 used computed tomography to examine the incidence of SIJ degeneration after lumbar fusion and reported that the incidence in the fixed fusion group was 75%, which was significantly higher than that in the floating fusion group (38.2%). Although Maigne et al 3 found no significant difference, they claimed that SIJP tended to occur more often in patients with fusion involving the sacrum. Similarly, in our study, the incidence of postoperative SIJP tended to be higher with fixed fusion. However, no significant difference was observed. Ha et al 37 indicated that there was no relationship between the number of fused segments and SIJ degeneration. However, it has been reported that an increase in the TABLE 5. Logistic Regression Analysis for SIJP After Lumbar/Lumbosacral Fusion Variables OR 95% CI P Value Fusion involving the sacrum Number of fused segments % CI indicates 95% confidence interval; OR, odds ratio; SIJP, sacroiliac joint pain. Spine

6 number of fused segments is associated with a risk of increased stress at SIJ. 38 Ivanov et al 38 assessed the angular motion of the sacrum and stress across SIJ using a finite element lumbar spine-pelvis model with simulated posterior fusion surgical procedures. They observed that posterior fusion of the lumbar spine resulted in increased stress across SIJ surfaces. Furthermore, the values of the parameters measured were related to the number of spinal segments involved. However, their study showed that greater stress was generated at SIJ in L4 S1 fusion than in L5 S1 fusion. In our study, it was confirmed that the incidence of postoperative SIJP increased associated with the number of fused segments; however, the incidence was unrelated to the presence of fusion involving the sacrum. Nagata et al 27 evaluated the change in lumbar facet loading and lumbosacral motion using four fresh canine cadaveric spines (unfused, T6 T13 fused, T6 L3 fused, and T6 L6 fused). They reported that immobilization of long segments of the spine influences the remaining mobile segments by increasing the load and motion not only at the immediately adjacent segment but also at the distal segments. Their study showed that caudal facet loading and lumbosacral motion were affected by the immobilization of proximal segments. Although they did not evaluate SIJ, SIJ is the joint adjacent to the lumbosacral segment. Therefore, similar biomechanical responses could also occur in SIJ. Their findings could support our result that fusion of multiple segments can increase the load at SIJ, regardless of whether the fusion involves the sacrum or not. In our study, the mechanisms of onset of SIJP after lumbar fusion could be as follows. One reason is the presence of fusion involving the sacrum, which could cause biomechanical responses similar to those observed in the case of ASD. The second reason is the fusion of multiple segments irrespective of whether the sacrum is fused or not. We consider that fusion of multiple segments can restrict the motion of the lumbar or thoracolumbar spine considerably depending on the number of involved spinal segments, consequently increasing the stress at SIJ. We believe that the latter mechanism is more involved in the development of SIJP after lumbar fusion. Recently, there has been an increase in the number of patients with osteoporotic kyphosis and adult spinal deformity. We believe that with improvement in the surgical skills of spine surgeons, spinal fusion techniques for multiple segments using instrumentation will increase considerably. When performing such surgery, in addition to ASD, SIJP should be kept in mind as a potential cause of LBP after lumbar fusion. Furthermore, we believe that preoperative diagnosis is very important. If SIJP is overlooked before fusion surgery, LBP would not only persist but also get worse after surgery. This study had several limitations. First, this was a retrospective study. Second, it is possible that the presence of SIJP before surgery could not be entirely removed. Although preoperative diagnosis was performed carefully, SIJ block was not performed in all patients. However, it is believed that in actual medical practice, it is not practical to perform an SIJ block in patients with no findings suggestive of SIJP. In the present study, we cannot rule out latent SIJP with no symptoms. This is believed to be because of the limitations of a retrospective study. However, we did conduct screening for SIJP before surgery as much as we possibly could. Therefore, we believe that our study shows the presence of SIJP as a potential cause of LBP to develop after lumbar/lumbosacral fusion. Key Points SIJP should not be overlooked as a cause of low back pain after lumbar spinal fusion. 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