The degenerative changes of the sacroiliac joint after S2 alar-iliac screw placement

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  • 1 Department of Orthopedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan
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OBJECTIVE

The goal of this study was to investigate clinical outcomes and risk factors for the progression of sacroiliac joint (SIJ) degeneration and bone formation after S2 alar-iliac screw (S2AIS) insertion.

METHODS

Using preoperative and follow-up CT scan findings (median follow-up 26 months, range 16–43 months), the authors retrospectively studied 100 SIJs in 50 patients who underwent S2AIS placement. The authors measured the progression of SIJ degeneration and bone formation after S2AIS insertion, postoperative new-onset SIJ pain, S2AIS-related reoperation, and instrumentation failures. Stepwise multivariate logistic regression modeling was performed to clarify the risk factors associated with the progression of SIJ degeneration.

RESULTS

Significant progression of SIJ degeneration was observed in 10% of the group with preoperative SIJ degeneration (p = 0.01). Bone formation was observed in 6.9% of joints. None of the patients with these radiographic changes had new-onset SIJ pain or underwent reoperation related to instrumentation failures. Multivariate logistic regression analysis revealed that preoperative SIJ degeneration (p < 0.01) and a young age at surgery (p = 0.03) significantly affected the progression of SIJ degeneration.

CONCLUSIONS

The progression of SIJ degeneration and bone formation neither led to major screw-related complications nor affected the postoperative clinical course during the median follow-up period of 26 months. Although S2AIS insertion is a safe procedure for most patients, the results of this study suggested that preoperative degeneration and younger age at surgery affected SIJ degeneration after S2AIS insertion. Further long-term observation may reveal other effects of S2AIS insertion on SIJ degeneration.

ABBREVIATIONS

IBF = interbody fusion; PLF = posterolateral fusion; PLIF = posterior lumbar interbody fusion; SIJ = sacroiliac joint; S2AIS = S2 alar-iliac screw; TLIF = transforaminal lumbar interbody fusion.

OBJECTIVE

The goal of this study was to investigate clinical outcomes and risk factors for the progression of sacroiliac joint (SIJ) degeneration and bone formation after S2 alar-iliac screw (S2AIS) insertion.

METHODS

Using preoperative and follow-up CT scan findings (median follow-up 26 months, range 16–43 months), the authors retrospectively studied 100 SIJs in 50 patients who underwent S2AIS placement. The authors measured the progression of SIJ degeneration and bone formation after S2AIS insertion, postoperative new-onset SIJ pain, S2AIS-related reoperation, and instrumentation failures. Stepwise multivariate logistic regression modeling was performed to clarify the risk factors associated with the progression of SIJ degeneration.

RESULTS

Significant progression of SIJ degeneration was observed in 10% of the group with preoperative SIJ degeneration (p = 0.01). Bone formation was observed in 6.9% of joints. None of the patients with these radiographic changes had new-onset SIJ pain or underwent reoperation related to instrumentation failures. Multivariate logistic regression analysis revealed that preoperative SIJ degeneration (p < 0.01) and a young age at surgery (p = 0.03) significantly affected the progression of SIJ degeneration.

CONCLUSIONS

The progression of SIJ degeneration and bone formation neither led to major screw-related complications nor affected the postoperative clinical course during the median follow-up period of 26 months. Although S2AIS insertion is a safe procedure for most patients, the results of this study suggested that preoperative degeneration and younger age at surgery affected SIJ degeneration after S2AIS insertion. Further long-term observation may reveal other effects of S2AIS insertion on SIJ degeneration.

In Brief

Researchers investigated risk factors for the progression of sacroiliac joint (SIJ) degeneration after S2 alar-iliac screw insertion. Preoperative SIJ degeneration and young age at surgery had a significant association with the progression of SIJ degeneration. There is a possibility that S2 alar-iliac screws may affect pre-existing degeneration and the progression of SIJ degeneration in younger patients. Further long-term observation may reveal other effects of S2 alar-iliac screw insertion on SIJ degeneration.

The iliac screw has gained popularity because of its ability to provide robust caudal anchoring, thereby helping to prevent complications related to spine surgery in the lumbosacral junction.1,2 However, conventional iliac screws have some disadvantages. O’Shaughnessy et al.3 reported that conventional screws were removed from 6.1% of patients because of hip/buttock pain and soft-tissue damage. To overcome these disadvantages, Kebaish4 and O’Brien et al.5 proposed the use of the S2 alar-iliac screw (S2AIS).

The S2AIS has advantages such as less skin protrusion and ease of alignment with adjacent pedicle screws. Additionally, the S2AIS crosses three cortical surfaces and provides excellent mechanical strength.6–8 Nevertheless, the S2AIS may damage the sacroiliac joint (SIJ) and accelerate degenerative changes, thereby affecting clinical symptoms and durability of S2AIS. Although sacropelvic fixation provides excellent stabilization of the lumbosacral construct,9,10 few studies have evaluated the progression of SIJ degeneration and bone fusion after S2AIS insertion.

Therefore, the primary purpose of this study was to evaluate the progression of SIJ degeneration and bone fusion following S2AIS placement performed with the aid of CT imaging. The secondary purpose was to report the risk factors for SIJ degeneration and the postoperative course related to these radiographic changes after S2AIS insertion.

Methods

This retrospective study was approved by the research ethics committee of our institution. We analyzed data from consecutive patients who underwent spine surgery using S2AISs at our hospital between 2012 and 2015. Those with primary and metastatic tumors and rheumatoid arthritis were excluded. Patients were only included if they had both preoperative and postoperative plain radiographs and CT scans available. Finally, 100 S2AIS constructs in 50 consecutive patients were assessed.

Clinical data including sex, age at surgery, diagnosis, number of fused discs, fusion procedure in L5/S1 (either an interbody fusion [IBF] procedure or a non-IBF procedure), number of patients with postoperative new-onset SIJ pain, and reoperation related to S2AIS were gathered from medical records. The IBF group included posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF); the non-IBF group included posterolateral fusion (PLF). Diagnoses were classified into the following 5 categories: adjacent-segment degeneration, failed back syndrome, lumbar canal stenosis at multiple disc levels, fracture, and infection. New-onset postoperative SIJ pain was defined as a new pain that emerged postoperatively and could be immediately relieved by local anesthesia.

Preoperative and follow-up (more than 1 year after surgery) CT scans and radiographs were collected for analysis. All images were reviewed by the senior author (S.F.). To evaluate the interobserver reliability of the radiological assessments, an orthopedic surgeon (K. Masamoto) reviewed the images independently in a blinded fashion.

Analysis of Insertion Accuracy of S2AIS and Postoperative Complications

We confirmed the insertion accuracy of S2AIS and postoperative complications by using CT scans. Partial screw misplacement was defined when the screw tip perforated the outer or inner pelvic cortex but a partial contact area between the screw tip and pelvis remained (Fig. 1). Complete screw misplacement was defined as no contact area between the screw tip and pelvis. Furthermore, organ damage (vessels, intestinal tract, and gluteus muscles) and clinical symptoms related to screw misplacement were confirmed. Instrumentation failures such as backout, breakage and loosening of S2AIS, and rod fracture or dislodgment were evaluated. Screw loosening was defined as ≥ 2-mm peri-screw lucency on CT images (Fig. 2). To evaluate the fusion status of the lumbosacral junction, an L5/S1 fusion status was defined according to the following criteria. An L5/S1 fusion was determined based on the report by Fujibayashi et al.11 In cases of PLIF and TLIF, fusion was defined as the osseous continuity between the cage and end plate without cyst development. In PLF cases, pseudarthrosis was defined as a continuous gap of ≥ 1 mm around the grafted bone.

FIG. 1.
FIG. 1.

Classification and example of screw perforation. Perforation cases were classified according to whether the screw tip contacted the pelvis—note that the screw tip was partially in contact with the pelvis (arrow). This case is an example of partial screw misplacement.

FIG. 2.
FIG. 2.

Definition and representative case of screw loosening. CT images depicting peri-screw lucency of ≥ 2 mm (arrows), which was diagnosed as S2AIS loosening.

Evaluation of Degeneration and Bone Fusion in the SIJ

We assessed SIJ degeneration and bone fusion. To determine whether the preoperative status of the SIJ affected the progression of degeneration after S2AIS placement, the 100 SIJs were classified into two groups: with and without preoperative degeneration. The preoperative bone fusion status was similarly classified. Using this classification, the progression of SIJ degeneration and bone formation were determined by comparing the preoperative and follow-up statuses.

SIJ degeneration was defined as one or more of the following criteria reported by Elgafy et al.12 and Ha et al.:13 subchondral sclerotic change in the entire SIJ (sacral side > 3 mm and iliac side > 5 mm), osteophyte formation beyond the SIJ, joint space narrowing (< 2 mm), and subchondral cysts and erosion. However, cases with only vacuum changes in the SIJ were excluded because previous reports showed that this change may be caused by aging.13 A bony bridge in the SIJ space was defined as SIJ bone fusion. We reported whether the instrumentation failures and new-onset SIJ pain occurred in patients who had progression of SIJ degeneration and bone formation.

Evaluation for Risk Factors Associated With Progression of Degenerative Changes

We analyzed the risk factors associated with progression of degenerative changes by using univariate and stepwise multivariate regression analysis. Progression of degeneration was set as the dependent variable. The following 11 factors were used for fitting regression models: sex, age at surgery, number of fused discs, surgical fusion procedure in L5/S1, L5/S1 fusion status, rod dislodgment, rod fracture, S2AIS loosening, thread type of S2AIS, and preoperative radiographic features of the SIJ (preoperative SIJ degeneration and bone fusion).

Surgical Procedure and S2AIS Characteristics

All S2AISs were inserted as previously reported.4,5 All surgeries were performed by two experienced spine surgeons. For this study, we selected the posterior approach and open insertion technique. The entry point of the S2AIS was 5 mm lateral and 5 mm caudal to the S1 hiatus and was created using a high-speed drill. The screw trajectory was angled from the entry point to the area above the sciatic notch. The screw was placed in the SIJ while observing the anteroposterior view of a fluoroscopic image. After switching to the use of the axial view of the SIJ, the screw was advanced to the area above the sciatic notch. We commonly used fully threaded S2AISs; moreover, only 2 patients were treated with partially threaded S2AISs. All screws were 8.5–10.5 mm in diameter and 70–100 mm in length. Two S2AIS head types were analyzed: the open-head S2AIS and the closed-head S2AIS.

If any degeneration in the L5/S1 disc was observed, IBF (PLIF or TLIF) at the L5/S1 was performed. PLF (non-IBF) was performed only when the disc at L5/S1 was completely intact before surgery. A morselized autograft was placed between the transverse processes and the lateral space in the lumbosacral area during decompression. Additional decortication and bone grafting were not performed in the SIJ.

Statistical Analysis

The interrater reliability of evaluating SIJ degeneration and bone fusion was determined. The kappa statistic was calculated to verify the interrater reliability and to determine the level of agreement between two observers.14 Fisher’s exact test was performed to assess whether the progression of SIJ degeneration was affected by preoperative degeneration, and the occurrence rate of new bone formation was also calculated.

We performed univariate and stepwise multivariate logistic regression analysis to identify the risk factors for progression of SIJ degeneration, while adjusting for confounding variables. Variables (p < 0.30) identified in univariate analysis were then included in multivariate analysis. A predictive variable was finally selected with forward stepwise entry (p < 0.05 for entry). Odds ratios and 95% confidence intervals were obtained. All statistical analyses were performed using SPSS software version 27.0 (IBM Corp.) and JMP (SAS Institute, Inc.). A p value < 0.05 was considered statistically significant.

Results

Patient Demographics

This study included 20 men and 30 women; the median age at surgery was 71 years (range 63–74.8 years) (Table 1). All patients underwent preoperative and follow-up CT scans (median 26 months, range 16–43 months). Twenty-five patients (50%) underwent surgery for adjacent-segment degeneration, 13 (26%) for failed back syndrome, 10 (20%) for multiple disc levels, and 1 (2%) for a fracture or infection. The median number of fused discs was 4 (range 3–8); 45 (90%) patients underwent the IBF procedure, and 5 (10%) underwent the non-IBF procedure. Only 1 (2%) patient reported new-onset SIJ pain postoperatively. This patient experienced pain at the right SIJ 5 years postoperatively; however, it was immediately relieved after an SIJ block was performed using local anesthesia. In this case, instrumentation failure, other postoperative complications, the progression of SIJ degeneration, and bone formation were not observed. The reoperation rate was 2% (1/50 cases) because of rod dislodgment caused by screw head breakage of the S2AIS.

TABLE 1.

Summary of demographic data in 50 patients who underwent S2AIS placement

VariableValue
Sex, no. (%)
 Male20 (40)
 Female30 (60)
Age at surgery in yrs (IQR)71 (63–74.8)
Diagnosis, no. (%)
 ASD25 (50)
 FBS13 (26)
 m-LCS10 (20)
 Fracture1 (2)
 Infection1 (2)
No. of fused discs (IQR)4 (3–8)
Fusion procedure in L5/S1, no. (%)
 IBF45 (90)
 Non-IBF5 (10)
No. of pts (%) w/ postop new-onset SIJ pain1 (2)
Reop, no. (%)*1 (2)

ASD = adjacent-segment disease; FBS = failed back syndrome; IQR = interquartile range; m-LCS = lumbar canal stenosis at multiple disc levels; pts = patients. Values are expressed as median and IQR or absolute number (n) and percentage (%).

This patient underwent reoperation for S2AIS head breakage and rod dislocation.

Insertion Accuracy of S2AIS and Complications Related to the Instrumentation

The S2AIS insertion accuracy and instrumentation failures are summarized in Table 2. There were 3 cases of partial screw misplacement. However, complete screw misplacement, vital organ damage, and symptoms of vital organ damage were not observed.

TABLE 2.

Insertion accuracy of S2AIS and postoperative complications

VariableNo. (%)
Partial screw misplacement, n = 100
 Outer cortex2 (2)
 Inner cortex1 (1)
Complete screw misplacement, n = 100
 Outer cortex0 (0)
 Inner cortex0 (0)
Organ damage caused by perforation, n = 1000 (0)
Clinical symptoms caused by perforation, n = 1000 (0)
Backout & breakage of S2AIS, n = 1000 (0)
Rod dislocation due to screw head breakage of the S2AIS, n = 50*2 (4)
Rod fracture, n = 502 (4)
L5/S1 pseudarthrosis, n = 508 (16)

Values are expressed as absolute number (no.) and percentage (%).

All screws were the closed-head type; 1 patient underwent reoperation.

Rod dislodgment caused by S2AIS head breakage was observed in 2 cases (4%). All cases of breakage involved the closed-head S2AIS. A representative case of rod dislodgment caused by screw head breakage is shown in Supplementary Fig. 1. Rod fracture was also observed in 2 patients (4%), and all fractures occurred at the L5/S1 level. L5/S1 pseudarthrosis was found in 16% of the patients; the overall S2AIS loosening rate was 15%.

Degenerative Change Progression and Bone Formation After S2AIS Placement

Evaluation of SIJ degeneration and bone fusion on CT images yielded kappa statistics of 0.94 and 0.85, respectively. The interrater reliability was excellent.

The overall rate of the progression of degeneration was 10% (Table 3). Of the 100 SIJs, 80 exhibited no preoperative degeneration. Significant progression of degeneration was observed in the group with preoperative degeneration compared to the group without preoperative degeneration (p < 0.01). Representative CT scans of preoperative and postoperative SIJ with the progression of SIJ degeneration are shown in Fig. 3.

TABLE 3.

Summary of progression of degeneration and bone formation in the SIJ

DegenerationProgressionp Value*Bone FormationSIJ Bone Fusion at FU
YesNoYesNo
PreopPreop
 Yes, n = 18513<0.01 Yes, n = 13130
 No, n = 82577 No, n = 876 (6.9%)81 (93.1%)

FU = follow-up.

The overall rate of progression of SIJ degeneration is 10%. SIJ degeneration progressed significantly in the group with preoperative degeneration (p < 0.01).

FIG. 3.
FIG. 3.

CT images depicting degenerative change progression after S2AIS placement. Preoperative (A) and postoperative (B) SIJ. Preoperative CT image showing osteophyte formation and vacuum change. During the follow-up period, subchondral sclerotic changes and erosion became noticeable in the left SIJ.

Of the 100 SIJs, 87 exhibited no preoperative bone fusion. Bone formation occurred in 6 of 87 SIJs (6.9%) during follow-up. Images of a representative case of SIJ bone formation are shown in Fig. 4. Progression of degeneration was observed in one of the patients with rod dislodgment. However, no progression of degeneration was confirmed in the patients who had other instrumentation failures, new-onset SIJ pain, or history of reoperation.

FIG. 4.
FIG. 4.

Representative case of bone fusion after S2AIS placement. CT scans depicting representative bone fusion in the SIJ before surgery (A) and at follow-up (B). Both SIJs were filled with bone, and the gap was completely closed at 1 year after S2AIS placement.

Risk Factors Affecting the Progression of SIJ Degeneration

In the univariate analysis, preoperative SIJ degeneration was significantly associated with the progression of degeneration (Table 4). Then, the potential risk factors identified in univariate analysis (sex, age at surgery, rod dislodgment, and preoperative SIJ degeneration) were included in a multivariate regression model. In stepwise multivariate logistic regression analysis, preoperative SIJ degeneration and age at surgery had a significant association with the progression of degenerative changes (OR 13.5 and 0.9, 95% CI 2.5–74.5 and 0.85–0.99; p < 0.01, p = 0.03, respectively) (Table 4). These results show that preoperative SIJ degeneration was the most important risk factor, and that younger age at surgery was also associated with the progression of SIJ degeneration.

TABLE 4.

Univariate and multivariate logistic regression analysis of risk factors for the progression of degeneration

VariableUnivariateMultivariate
OR (95% CI)p ValueOR (95% CI)p Value*
Sex
 Male0.4 (0.08–2.0)0.270.78 (0.13–4.69)0.79
 FemaleReferenceReference
Age at surgery1.0 (0.90–1.02)0.230.9 (0.85–0.99)0.03
No. of fused discs0.96 (0.75–1.22)0.72NANA
Surgical fusion procedure in L5/S1
 IBFReference>0.99NANA
 Non-IBF0.0 (0.0–inf)NANA
L5/S1 fusion status
 PseudarthrosisReference0.73NANA
 Fusion0.8 (0.2–3.1)NANA
Rod dislodgment
 NoReference0.3Reference0.69
 Yes0.3 (0.0–2.9)0.6 (0.04–9.15)
Rod fracture
 NoReference>0.99NANA
 Yes0.0 (0.0–inf)NANA
S2AIS loosening
 NoReference>0.99NANA
 Yes0.0 (0.0–inf)NANA
Thread type of S2AIS
 Full threadReference>0.99 NA
 Partial thread0.0 (0.0–inf)NANA
Preop SIJ degeneration
 NoReference<0.01Reference<0.01
 Yes7.5 (1.8–31.7)13.5 (2.5–74.5)
Preop SIJ bone fusion
 NoReference>0.99NANA
 Yes0.0 (0.0–inf)NANA

Inf = infinity; NA = not applicable.

Statistically significant difference (p < 0.05).

Discussion

We analyzed the progression of SIJ degeneration and bone formation following S2AIS insertion. SIJ degeneration was significantly accelerated in the population with preoperative degeneration. Spontaneous bone formation was noted in 6.9% of the cases after a median follow-up of 26 months (range 16–43 months). We also demonstrated two significant risk factors for the progression of degeneration: the existence of preoperative SIJ degeneration and younger age at surgery.

To the best of our knowledge, this study was the first report to present the risk factors for the progression of SIJ degeneration after S2AIS placement and the relationship between radiographic changes and postoperative new-onset SIJ pain after S2AIS placement. Few studies have analyzed radiographic changes of the SIJ after sacroiliac fixation based on CT scan findings.

As for the plain iliac screws, Ohtori et al.15 reported the radiographic outcomes of 20 patients after iliac screw insertion. These authors concluded that degenerative progressions of SIJ were not seen within 3 years after surgery in which plain iliac screws were used. Mazur et al. also reported the radiographic outcomes of 13 cases with a minimum follow-up of 12 months after S2AIS placement.8 They found that none of the screws were malpositioned, the L5/S1 bone fusion rate was 92%, and the S2AIS loosening rate was 27%. Moreover, no major screw-related complications and degenerative change progression in the SIJ were noted for almost 1 year postsurgery. The abovementioned results of clinical outcome after S2AIS placement were consistent with our results. Moreover, the present study, which included 50 patients, further clarified that the progression of SIJ degeneration occurred over time in a subset of patients.

Regarding the instrumentation failures, rod dislodgment was observed in 2 cases (4%). Of these, the progression of degeneration was noted in one patient and the reoperation was performed for the other patient (2%). In the 2 cases, rod dislodgment was caused by screw head breakage of S2AIS, and the screw head was a closed-head type. The closed-head screw has a restricted and rigid structure in which the rod is surrounded by the screw head without an additional screw. Hence, the correction force directly impacted the screw heads, and the metal was subsequently torn.

These findings suggested that the closed-head S2AIS could result in adverse consequences. Other instrumentation failures or reoperations were not found in the patients in whom there was progression of degeneration. Considering these results, we concluded that the progression of degeneration itself could not have caused the instrumentation failures.

We evaluated the risk of SIJ degeneration by using multivariable logistic regression analysis. We found that the independent risk factors were preoperative SIJ degeneration and age at surgery. The existence of preoperative SIJ degeneration was the most significant risk factor. This finding suggests that inherent degeneration was accelerated by S2AIS insertion.

Figure 4 shows a characteristic case of progression of degeneration and joint erosion. Joint destruction progressed in the long term. Fortunately, the progression of SIJ degeneration did not lead to reoperation or serious adverse events in our study. Nevertheless, consideration for preoperative degeneration and long-term follow-up should be given because the long-term effects of SIJ degeneration after S2AIS placement remain unknown. We found that the age at surgery was also a risk factor for the progression of degeneration. This suggests that a younger age preoperatively was associated with an increased risk of degenerative changes.

Eno et al.16 reported that the prevalence of SIJ degeneration steadily increased with age in asymptomatic adults. However, our result was different from the preceding report on a normative population, and it suggests that penetration of the SIJ using S2AISs may affect the progression of SIJ degeneration in younger patients. Therefore, the use of S2AISs for younger patients should be given consideration before surgery.

In the present study, only 1 patient reported SIJ pain after surgery. The reported prevalence rates of SIJ pain following lumbar spine surgery are in the range of 3%–6.6%.17–19 The underlying mechanisms and clinical properties of SIJ pain are controversial because SIJ is a complex joint that transmits load from the spine to the lower extremities.20,21

A previous study stated that 75% of patients reported SIJ pain following conventional iliac screw placement.15 However, a recent study suggested that sacropelvic fixation reduced the incidence of SIJ pain after long fusion.20 Baria et al. demonstrated that S2AIS reduced vertical motion on the SIJ during flexion-extension loading in their biomechanical test.22 SIJ fusion is also used to treat refractory SIJ pain.21,23 Therefore, spinal fusion using SIJ fixation did not necessarily increase the incidence of SIJ pain after surgery. Our study, which used S2AIS, indicated a lower incidence of postoperative SIJ pain than previous reports; bone formation in SIJ also occurred over time.15,17–19 Based on these results, direct fixation using S2AIS and SIJ bone formation after S2AIS insertion may reduce postoperative SIJ pain. Although changes over time were noted on radiographic images, our study suggests that SIJ pain after S2AIS placement is rare.

This study has some limitations. First, this was a retrospective, single-center study. Prospective long-term observation can provide information regarding degeneration and instrumentation failure during long-term follow-up. Second, this study did not include a control group. Hence, further investigations including a control group (for example, a group of patients who have undergone iliac screw placement or natural SIJ degeneration) are required to assess the more precise effects of S2AISs. Third, regarding the clinical symptoms related to the SIJ, we defined new-onset SIJ pain according to medical records. In a future study, it may be useful to include other symptoms or disability in daily life such as stiffness in the lumbosacral region and hip.

Conclusions

The progression of degeneration and bone formation after a median follow-up of 26 months (range 16–43 months) did not affect the postoperative clinical outcome. S2AIS rarely leads to major instrumentation failures and complications. However, S2AIS use was a disadvantage to a subset of patients. There is a possibility that preoperative degeneration was accelerated and the progression of SIJ degeneration in younger patients was distorted by S2AIS insertion. The long-term effects of S2AIS on the SIJ remain unknown. Therefore, consideration for using S2AISs in this population should be given before surgery.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Ikeda, Fujibayashi, Otsuki. Acquisition of data: Masamoto, Murata. Analysis and interpretation of data: Ikeda, Fujibayashi, Masamoto, Murata. Drafting the article: Ikeda, Fujibayashi, Otsuki, Masamoto, T Shimizu, Y Shimizu, Murata. Critically revising the article: Ikeda, Fujibayashi, Otsuki, Masamoto, T Shimizu, Y Shimizu, Murata. Reviewed submitted version of manuscript: all authors. Statistical analysis: Ikeda. Study supervision: Fujibayashi, Matsuda.

Supplemental Information

Online-Only Content

Supplemental material is available with the online version of the article.

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    Cho DY, Shin MH, Hur JW, et al. Sagittal sacropelvic morphology and balance in patients with sacroiliac joint pain following lumbar fusion surgery. J Korean Neurosurg Soc. 2013;54(3):201206.

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  • 20

    Unoki E, Miyakoshi N, Abe E, et al. Sacropelvic fixation with S2 alar iliac screws may prevent sacroiliac joint pain after multisegment spinal fusion. Spine (Phila Pa 1976).2019;44(17):E1024E1030.

    • Crossref
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  • 21

    Rashbaum RF, Ohnmeiss DD, Lindley EM, et al. Sacroiliac joint pain and its treatment. Clin Spine Surg. 2016;29(2):4248.

  • 22

    Baria D, Lindsey RW, Milne EL, et al. Effects of lumbosacral arthrodesis on the biomechanics of the sacroiliac joint. JBJS Open Access. 2020;5(1):e0034.

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    Zaidi HA, Montoure AJ, Dickman CA. Surgical and clinical efficacy of sacroiliac joint fusion: a systematic review of the literature. J Neurosurg Spine. 2015;23(1):5966.

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Supplementary Materials

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    Classification and example of screw perforation. Perforation cases were classified according to whether the screw tip contacted the pelvis—note that the screw tip was partially in contact with the pelvis (arrow). This case is an example of partial screw misplacement.

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    Definition and representative case of screw loosening. CT images depicting peri-screw lucency of ≥ 2 mm (arrows), which was diagnosed as S2AIS loosening.

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    CT images depicting degenerative change progression after S2AIS placement. Preoperative (A) and postoperative (B) SIJ. Preoperative CT image showing osteophyte formation and vacuum change. During the follow-up period, subchondral sclerotic changes and erosion became noticeable in the left SIJ.

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    Representative case of bone fusion after S2AIS placement. CT scans depicting representative bone fusion in the SIJ before surgery (A) and at follow-up (B). Both SIJs were filled with bone, and the gap was completely closed at 1 year after S2AIS placement.

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  • 19

    Cho DY, Shin MH, Hur JW, et al. Sagittal sacropelvic morphology and balance in patients with sacroiliac joint pain following lumbar fusion surgery. J Korean Neurosurg Soc. 2013;54(3):201206.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20

    Unoki E, Miyakoshi N, Abe E, et al. Sacropelvic fixation with S2 alar iliac screws may prevent sacroiliac joint pain after multisegment spinal fusion. Spine (Phila Pa 1976).2019;44(17):E1024E1030.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Rashbaum RF, Ohnmeiss DD, Lindley EM, et al. Sacroiliac joint pain and its treatment. Clin Spine Surg. 2016;29(2):4248.

  • 22

    Baria D, Lindsey RW, Milne EL, et al. Effects of lumbosacral arthrodesis on the biomechanics of the sacroiliac joint. JBJS Open Access. 2020;5(1):e0034.

  • 23

    Zaidi HA, Montoure AJ, Dickman CA. Surgical and clinical efficacy of sacroiliac joint fusion: a systematic review of the literature. J Neurosurg Spine. 2015;23(1):5966.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

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