Sacropelvic fixation versus fusion to the sacrum for spondylodesis in multilevel degenerative spine disease

Preoperative and follow-up variations of psoas major muscle are related to S1 screw loosening in patients with degenerative lumbar spinal stenosis

BACKGROUND

It was reported the paraspinal muscle played an important role in spinal stability. The preoperative paraspinal muscle was related to S1 screw loosening. But the relationship between preoperative and postoperative change of psoas major muscle (PS) and S1 pedicle screw loosening in degenerative lumbar spinal stenosis (DLSS) patients has not been reported. This study investigated the effects of preoperative and follow-up variations in the psoas major muscle (PS) on the first sacral vertebra (S1) screw loosening in patients with DLSS.

METHODS

212 patients with DLSS who underwent lumbar surgery were included. The patients were divided into the S1 screw loosening group and the S1 screw non-loosening group. Muscle parameters were measured preoperatively and at last follow-up magnetic resonance imaging. A logistic regression analysis was performed to investigate the risk factors for S1 screw loosening.

RESULTS

The S1 screw loosening rate was 36.32% (77/212). The relative total cross-sectional areas and relative functional cross-sectional areas (rfCSAs) of the PS at L2-S1 were significantly higher after surgery. The increased rfCSA values of the PS at L3-S1 in the S1 screw non-loosening group were significantly higher than those in the S1 screw loosening group. The regression analysis showed male, lower CT value of L1 and longer segment fusion were independent risk factors for S1 screw loosening, and postoperative hypertrophy of the PS was a protective factor for S1 screw loosening.

CONCLUSIONS

Compared to the preoperative muscle, the PS size increased and fatty infiltration decreased after surgery from L2-3 to L5-S1 in patients with DLSS after short-segment lumbar fusion surgery. Postoperative hypertrophy of the PS might be considered as a protective factor for S1 screw loosening. MRI morphometric parameters and postoperative selected exercise of PS for DLSS patients after posterior lumbar fusion surgery might contribute to improvement of surgical outcome.

Biomechanical evaluation of multiple pelvic screws and multirod construct for the augmentation of lumbosacral junction in long spinal fusion surgery

Background: Posterior long spinal fusion was the common procedure for adult spinal deformity (ASD). Although the application of sacropelvic fixation (SPF), the incidence of pseudoarthrosis and implant failure is still high in long spinal fusion extending to lumbosacral junction (LSJ). To address these mechanical complications, advanced SPF technique by multiple pelvic screws or multirod construct has been recommended. This was the first study to compare the biomechanical performance of combining multiple pelvic screws and multirod construct to other advanced SPF constructs for the augmentation of LSJ in long spinal fusion surgery through finite element (FE) analysis.

Methods: An intact lumbopelvic FE model based on computed tomography images of a healthy adult male volunteer was constructed and validated. The intact model was modified to develop five instrumented models, all of which had bilateral pedicle screw (PS) fixation from L1 to S1 with posterior lumbar interbody fusion and different SPF constructs, including No-SPF, bilateral single S2-alar-iliac (S2AI) screw and single rod (SS-SR), bilateral multiple S2AI screws and single rod (MS-SR), bilateral single S2AI screw and multiple rods (SS-MR), and bilateral multiple S2AI screws and multiple rods (MS-MR). The range of motion (ROM) and stress on instrumentation, cages, sacrum, and S1 superior endplate (SEP) in flexion (FL), extension (EX), lateral bending (LB), and axial rotation (AR) were compared among models.

Results: Compared with intact model and No-SPF, the ROM of global lumbopelvis, LSJ, and sacroiliac joint (SIJ) was decreased in SS-SR, MS-SR, SS-MR, and MS-MR in all directions. Compared with SS-SR, the ROM of global lumbopelvis and LSJ of MS-SR, SS-MR, and MS-MR further decreased, while the ROM of SIJ was only decreased in MS-SR and MS-MR. The stress on instrumentation, cages, S1-SEP, and sacrum decreased in SS-SR, compared with no-SPF. Compared with SS-SR, the stress in EX and AR further decreased in SS-MR and MS-SR. The most significantly decreased ROM and stress were observed in MS-MR.

Conclusion: Both multiple pelvic screws and multirod construct could increase the mechanical stability of LSJ and reduce stress on instrumentation, cages, S1-SEP, and sacrum. The MS-MR construct was the most adequate to reduce the risk of lumbosacral pseudarthrosis, implant failure, and sacrum fracture. This study may provide surgeons with important evidence for the application of MS-MR construct in the clinical settings.

L5-S1 nonunion occurrence even after anterior column support combined with iliac screw fixation in long fusion for adult spinal deformity: CT-based analysis at 2-year follow-up

OBJECTIVE

Iliac screw fixation and anterior column support are highly recommended to prevent lumbosacral pseudarthrosis after long-level adult spinal deformity (ASD) surgery. Despite modern instrumentation techniques, a considerable number of patients still experience nonunion at the lumbosacral junction. However, most previous studies evaluating nonunion relied only on plain radiographs and only assessed when the implant failures occurred. Therefore, using CT, it is important to know the prevalence after iliac fixation and to evaluate risk factors for nonunion at L5-S1.

METHODS

Seventy-seven patients who underwent ≥ 4-level fusion to the sacrum using iliac screws for ASD and completed a 2-year postoperative CT scan were included in the present study. All L5-S1 segments were treated by interbody fusion. Lumbosacral fusion status was evaluated on 2-year postoperative CT scans using Brantigan, Steffee, and Fraser criteria. Risk factors for nonunion were analyzed using patient, surgical, and radiographic factors. The metal failure and its association with fusion status at L5-S1 were evaluated.

RESULTS

Of the 77 patients, 12 (15.6%) showed nonunion at the lumbosacral junction on the 2-year CT scans. Multivariate analysis using logistic regression revealed that only higher American Society of Anesthesiologists (ASA) grade was a risk factor for nonunion (OR 25.6, 95% CI 3.196-205.048, p = 0.002). There were no radiographic parameters associated with fusion status at L5-S1. Lumbosacral junction rod fracture occurred more frequently in patients with nonunion than in patients with fusion (33.3% vs 6.2%, p = 0.038).

CONCLUSIONS

Although iliac screw fixation and anterior column support have been performed to prevent lumbosacral nonunion during ASD surgery, 15.6% of patients still showed nonunion on 2-year postoperative CT scans. High ASA grade was a significant risk factor for nonunion. Rod fracture between L5 and S1 occurred more frequently in the nonunion group.

Prediction of Sacral Screw Loosening after Lumbosacral Surgeries Involving Rigid Fixation of Sacral Bone Using Preoperative Computed Tomography Scans

Objective

To find a preoperative computed tomography-based method to predict the incidence of sacral screw loosening and assist surgical planning.

Methods

Surgically treated patients for degenerative lumbosacral disorders with rigid pedicle screw fixation of patients with L5-S1 vertebra in our center from January 2016 to January 2021 were retrospectively included in the current study. CT scan attenuation of the horizontal plane of the sacrum was measured with Hounsfield units (HU). Postoperative X-ray tests were used to diagnose screw loosening. The data was analyzed by independent sample t-tests, X² analysis, Pearson correlation analysis, and ROC curve analysis.

Results

A total of 162 (114 male, 48 female, average age 63.7 ± 7.3 years) patients were included in the final analysis. Significant differences were found between the screw loosening group and nonloosening group concerning the HU value of the sacrum at the horizontal plane (P < 0.01). In ROC curve analysis, AUC was 0.674 (95% CI: 0.592-0.756). A cutoff of 200 HU provided 64.8% sensitivity and 62.4% specificity, and a cutoff of 150 HU provided 90.2% sensitivity.

Conclusions

Analyzing 162 patients with at least 12 months of follow-up, we propose cutoff CT attenuation values of 200 HU and 150 HU to take moderate and radical measures of screw augmentation to prevent screw loosening in the sacral bone.

The relationship between S1 screw loosening and postoperative outcome in patients with degenerative lumbar scoliosis

Background

When choosing S1 as the lowest level of instrumentation, there are many complications may come out such as S1 screw loosening. Facing this problem, there has been various techniques for the protection of S1 screw including sacropelvic fixation, bicortical or tricortical insertion of S1 screw.

Objective

This study aimed to explore the risk factors for the S1 screw loosening, then to demonstrate the relationship between S1 screw loosening and postoperative outcome for patients with degenerative lumbar scoliosis (DLS).

Methods

Patients who underwent lumbosacral fixation for DLS were evaluated retrospectively. They were divided into two groups according to the S1 pedicle screw at the follow-up. Age, gender, bone mineral density, body mass index, history of smoking, the number of instrumented levels, comorbidities, complications and radiological parameters were collected. We established logistic regression analysis to determine independent risk factors for S1 screw loosening and multiple linear regression to identify whether S1 screw loosening would influence postoperative clinical outcome.

Results

S1 screw loosening rate was up to 41.0% (32/78). Patients were older in the S1 screw loosening group than those in the control group (P < 0.05). Compared with the control group, the rate of osteoporosis was higher in screw loosening group than that in the control group (P < 0.05). Older age and osteoporosis were independent risk factors for S1 screw loosening (P < 0.05). In the screw loosening group, the rate of hypertension was higher than that in the control group (P < 0.05). The relationship of S1 screw loosening and ODI was not significant in the multiple linear regression (P > 0.05). The clinical outcome was similar in the S1 screw loosening group and control group (P > 0.05).

Conclusion

Older age and osteoporosis are independent risk factors for the S1 screw loosening. Patients with complication of S1 screw loosening are not always along with worse clinical outcome. We should consider potential benefit, complications and medical cost when choosing the lowest instrumented vertebrae for patients with DLS.

Is L5/S1 interbody fusion necessary in long-segment surgery for adult degenerative scoliosis? A systematic review and meta-analysis

OBJECTIVE

There is no consensus regarding the best surgical strategy at the lumbosacral junction (LSJ) in long constructs for adult spinal deformity (ASD). The use of interbody fusion (IF) has been advocated to increase fusion rates, with additional pelvic fixation (PF) typically recommended. The actual benefit of IF even when extending to the pelvis, however, has not been vigorously analyzed. The goal of this work was to better understand the role of IF, specifically with respect to arthrodesis, when extending long constructs to the ilium.

METHODS

A systematic review of the PubMed and Cochrane databases was performed to identify the relevant studies in English, addressing the management of LSJ in long constructs (defined as ≥ 5 levels) in ASD. The search terms used were as follows: "Lumbosacral Junction," "Long Constructs," "Long Fusion to the Sacrum," "Sacropelvic Fixation," "Interbody Fusion," and "Iliac Screw." The authors excluded technical notes, case reports, literature reviews, and cadaveric studies; pediatric populations; pathologies different from ASD; studies not using conventional techniques; and studies focused only on alignment of different levels.

RESULTS

The PRISMA protocol was used. The authors found 12 retrospective clinical studies with a total of 1216 patients who were sorted into 3 different categories: group 1, using PF or not (n = 6); group 2, using PF with or without IF (n = 5); and group 3, from 1 study comparing anterior lumbar interbody fusion versus transforaminal lumbar interbody fusion. Five studies in group 1 and 4 in group 2 had pseudarthrosis rate as primary outcome and were selected for a quantitative analysis. Forest plots were used to display the risk ratio, and funnel plots were used to look at the risk of publication bias. The summary risk ratios were 0.36 (0.23-0.57, p < 0.001) and 1.03 (0.54-1.96, p = 0.94) for the PF and IF, respectively; there is a protective effect of overall pseudarthrosis for using PF in long constructs for ASD surgeries, but not for using IF.

CONCLUSIONS

The long-held contention that L5/S1 IF is always advantageous in long-construct deformity surgery is not supported by the current literature. Based on the findings from this systematic review and meta-analysis, PF with or without additional L5/S1 interbody grafting demonstrates similar overall construct pseudarthrosis rates. The added risk and costs associated with IF, therefore, should be more closely considered on a case-by-case basis.

Pull-out strength evaluation of cement augmented iliac screws in osteoporotic spino-pelvic fixation

INTRODUCTION

Spino-pelvic fixation has been widely accepted for surgical treatment of sacral tumor, scoliosis surgery and pelvic fractures. Cement augmentation of screws is an option to improve implant stability in osteoporotic bone quality. Aim of the present study is to compare iliac screw fixation without cement fixation and two cement application options in a biomechanical testing.

HYPOTHESIS

Cement augmentation of iliac screws leads to superior pull-out strength.

MATERIAL AND METHODS

Thirty female and osteoporotic human iliac bones were used. Three operation treatment groups were generated: Screw fixation (cannulated screws) without cement augmentation [Operation treatment (OT) A], screw fixation with cement augmentation before screw placement (cannulated screws) (OT B) and screw fixation with perforated screws and cement augmentation after screw placement (OTC). Pull-out tests were performed with a rate of 6mm/min. A load versus displacement curve was generated. Maximum pull-out force (N) was measured in the load-displacement curve.

RESULTS

Paired group 1 (OT A vs. OT B): Screw fixation without cement augmentation: 592.6N±335.07 and screw fixation with cement augmentation before screw placement: 996N±287.43 (p=0.0042). Paired group 2 (OT A vs. OT C): screw fixation without cement augmentation: 716.2N±385.86 and fenestrated screw fixation with cement augmentation after screw placement: 1324.88N±398.76 (p=0.0489). Paired group 3 (OT B vs. OT C): Screw fixation with cement augmentation before screw placement: 1077.2±486.66 and fenestrated screw fixation with cement augmentation after screw placement: 1298.2N±726.19 (p=0.3286).

DISCUSSION

Regarding iliac screw fixation for spino-pelvic ostesynthesis in osteoporotic bone, cement augmentation is significantly superior to solid iliac screw fixation respecting pull-out-strength. Nevertheless, further biomechanical studies are needed to verify these findings.

LEVEL OF EVIDENCE

Not applicable; biomechanical cadaver study.

The Comparison of Spinopelvic Parameters, Complications, and Clinical Outcomes After Spinal Fusion to S1 with or without Additional Sacropelvic Fixation for Adult Spinal Deformity: A Systematic Review and Meta-analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVE

The purpose of the study was to compare the outcomes and after spinal fusion with or without iliac screw (IS) insertion for patients with adult spinal deformity (ASD).

SUMMARY OF BACKGROUND DATA

The number of patients undergoing multilevel spinal stabilization for the treatment of ASD is growing. However, the selection of spinopelvic fixation for ASD patients with long fusion is controversial.

METHODS

A comprehensive literature search was performed without time restriction according to the guidelines from the Cochrane Collaboration in May 2020 using PubMed, EMBASE, and the Cochrane Library. The comparison of the two types of fixation was evaluated by spinopelvic parameters, incidence rate of complications, rate of revision, and clinical outcomes at the last follow-up.

RESULTS

The literature search identified 422 records, of which eight studies were included for meta-analysis with a total of 439 patients. All the included studies provided level III evidence. There was no significant difference in the sagittal vertical axis, pelvic incidence, the proximal junctional kyphosis rates, the pseudarthrosis rates, the revision rates, and the clinical outcomes at the last follow-up between those who receive sacrum fixation and sacropelvic fixation. Nevertheless, greater lumbar lordosis (LL) (weighted mean difference [WMD], 4.15; 95% confidence interval [CI] 2.46-5.84, P < 0.01), greater sacral slope (SS) (WMD, 2.32; 95% CI 1.21-3.43, P < 0.01), and lower rate of the distal instrumentation instability (odds ratio, 0.25; 95% CI 0.10-0.61, P = 0.002) were observed in IS group between the comparison.

CONCLUSION

The clinical outcomes in the IS group were similar to those in the non-IS group, but the application of the IS significantly restored LL, prevented decompensation, and reduced the occurrence of the distal instrumentation instability. Therefore, the IS may be a good choice for the operative treatment of ASD patients with sagittal malalignment and other risks of lumbosacral fracture, metal breakage, and screw pullout.Level of Evidence: 3.

Incidence, Risk, and Outcome of Pedicle Screw Loosening in Degenerative Lumbar Scoliosis Patients Undergoing Long-Segment Fusion

STUDY DESIGN

Retrospective study.

OBJECTIVE

To investigate the incidence, risk factors, and outcomes of pedicle screw loosening in degenerative lumbar scoliosis (DLS) undergoing long-segment spinal fusion surgery.

METHODS

One hundred and thirty DLS patients who underwent long-segment fusion surgery with at least a 12-month follow-up were studied. The incidence and risk factors of screw loosening were investigated. VAS, SRS-22, and ODI scores were obtained preoperatively and at follow-up.

RESULTS

One hundred and sixty-eight of 1784 (9.4%) screws showed evidence of loosening in 71 (54.6%) patients. Three patients required revision surgery. Screw loosening rates according to vertebral insertion level were lowest instrumented vertebra (LIV): 45.4%; uppermost instrumented vertebra (UIV):17.7%; one vertebra above the LIV: 0.5%; 2 vertebrae above the LIV: 0.4%. Multiple logistic regression analysis of possible risk factors indicated that preoperative lateral subluxation ≥8 mm (odds ratio [OR]: 2.68, 95% confidence interval [CI]: 1.16-6.20), osteopenia (OR: 5.52, 95% CI: 1.64-18.56), osteoporosis (OR: 8.19, 95% CI: 2.40-27.97), fusion to sacrum (OR: 2.55, 95% CI: 1.12-5.83), postoperative TLK greater than 10° (OR: 2.63, 95% CI: 1.14-6.04) and SVA imbalance (OR: 3.44, 95% CI: 1.17-10.14) were statistically significant. No difference was noted in preoperative, follow-up, and change of VAS, ODI, and SRS-22 scores.

CONCLUSIONS

Screw loosening in DLS underwent long-segment surgery is common and tends to occur in the LIV or UIV. Lateral subluxation ≥8 mm, osteopenia, osteoporosis, fusion to the sacrum, postoperative TLK greater than 10°, and SVA imbalance were the independent influencing factors. Screw loosening can be asymptomatic, while longer-term follow-up is required.

SACROPELVIC FIXATION USING ILIAC SCREWS: EVALUATION OF TECHNIQUE AND COMPLICATIONS

ABSTRACT Sacropelvic fixation arose from the need to protect the sacral instrumentation in long constructions, due to failures in the implant-bone interface and the treatment of diseases in which there is no possibilities of sacral fixation such as infections and tumors. Due to anatomic difficulties and the complex spinopelvic biomechanics several techniques were developed. The fixation with iliac screws has become according to multiple studies, a well-established technique that minimizes frequent complications such as pseudoarthrosis and implant failure. However, it has disadvantages such as iliac wing fracture and skin lesions due to the protrusion of materials. The present study aims to comprehensively review the literature on the technique taking into account relevant aspects to its better knowledge and application. Level of evidence III; Therapeutic Study.

EVALUATION OF THE RESULTS OF PELVIC FIXATION IN LONG LUMBOSACRAL INSTRUMENTATIONS IN ELDERLY PATIENTS

ABSTRACT Objective: Evaluate the initial results and the possible complications of the combination of pelvic fixation using iliac screws in long instrumentations of the lumbar spine in elderly patients. Methods: An analysis of 38 patients who underwent lumbar spine arthrodesis instrumentation with more than 3 levels, in which we included level L5-S1 and extended the fixation to the iliac crest. Radiological assessment of instrumentation through X-ray of the lumbar spine and pelvis, and computed tomography, to investigate the presence of radiological fusion. Clinical evaluation through a questionnaire of buttock pain including the visual analogue pain score (VAS). Complications related to pelvic instrumentation were investigated. Results: All patients had radiological fusion in the lumbosacral transition. A halo was found around the iliac screw on imaging studies in 31% of patients, but without related symptoms. The questionnaire of buttock pain found that 15% of patients had some low intensity buttock pain (VAS 1-2) and no need to or interest in removing the screws. There was infection at the surgical site in 2% of cases, hematoma in the buttocks in 5%, and vertebral body fracture in the cranial level instrumented in 7% of cases. Conclusions: Pelvic fixation through the iliac screws proved to be effective in protecting the S1 screws in long instrumentations including the L5-S1 level in elderly patients, allowing the radiological bone fusion. The overall results for pain were satisfactory, based on a questionnaire of buttock pain. There are no signs of overload or degeneration of the sacroiliac joints in the early years after surgery. Level of Evidence IV; Case series - therapeutic study.

Novel L5-S1 interbody fusion technique for root anomalies or abnormal root configurations of L5-S1 foramens

Purpose

We show in this study that if a root anomaly does not permit access to the disc space in the usual way, the technique we define here can be used. If the patient has a root anomaly or an abnormal root configuration at this level, inevitably, an anterior approach is preferred.

Materials and Methods

The patient's previous skin incision was used; the L5-S1 space was reached laterally without entering the midline. The dura in the midline and the L5 and S1 roots on both sides were exposed. They were reached through the adjacent points of both S1 pedicles by going around the upper edge of the sacrum, allowing the disc space to be evacuated. An autologous bone graft was placed on both sides of the space. T10-S1 pedicle screws were placed. An L1 pedicle osteotomy was performed and joined using two rods.

Results

The patient's back and leg pain disappeared after the surgery. The plain X-rays showed that the sagittal balance was restored. In this case, it is impossible to see the disc space because the nerve root blocks its view.

Conclusions

The classic approach in such cases is to perform a fusion by either a transperitoneal or retroperitoneal approach or by performing a posterior intertransverse fusion. However, it is very challenging to execute an anterior L5-S1 fusion on a patient with pelvic retroversion. When the spinopelvic junction is included in the fusion, one common problem observed is pseudarthrosis. The surgical technique defined in this article makes it possible to drill the bone tissue through the disc space and the upper surface of the sacrum, accessing the pedicle bone. Then, a discectomy is performed at the disc space, a bone graft is placed, and a posterior lumbar interbody fusion is performed.

Possible factors associated with sagittal malalignment recurrence after pedicle subtraction osteotomy

PURPOSE

This retrospective study investigates sagittal alignment after pedicle subtraction osteotomy (PSO). The purpose was to investigate factors associated with malalignment recurrence.

METHODS

Full spine radiographs were analyzed in 66 patients (average age 54.5 years, follow-up 3.8 years). Measurements were taken preoperatively, 3 months postoperatively, at follow-up: SVA C2 and C7, C2-C7 lordosis, T4-T12 kyphosis, L1-S1 lordosis, PSO lordosis, pelvic incidence, pelvic tilt, sacral slope. Follow-up CTs were screened for pseudarthrosis and gas in sacroiliac joints.

RESULTS

PSO lordosis increased from 11.8° to 40.8° (p < 0.0001) and kept stable. Lumbar lordosis increased from 28.6° to 57.7° (p < 0.0001) and decreased to 49.7° (p = 0.0008). Pelvic tilt decreased from 29.2° to 16.5° (p < 0.0001) and increased to 22.5° (p < 0.0001). SVA C7 decreased from 105.1 to 35.5 mm (p < 0.0001) and increased to 64.8 mm (p = 0.0005). Twenty-eight patients (42%) had an SVA C7 increase of more than 70 mm in the postoperative course: recurrence group. These patients were older: 62.8 years versus 52.3 years (p = 0.0031). Loss of lordosis was 11.9° (recurrence group) versus 5.0° (non-recurrence group). Eleven patients (17%) had pseudarthrosis. Pelvic incidence increased by 9.3° (recurrence group) versus 3.8° (non-recurrence group). In 23 patients (35%), pelvic incidence increased > 10°. Gas was evidenced in sacroiliac joints in 22 patients (33%).

CONCLUSION

Postoperative anterior malalignment recurrence may occur after PSO. Elderly patients were at risk of recurrence. Loss of lumbar lordosis linked to pseudarthrosis represented another factor. With malalignment recurrence, anterior trunk rotation and pelvic retroversion might additionally have augmented moments across sacroiliac joints with subsequent ligament laxity and pelvic incidence increase. These slides can be retrieved under Electronic Supplementary Material.

Is S1 Alar Iliac Screw a Feasible Option for Lumbosacral Fixation?: A Technical Note

Nonunion at the lumbosacral junction is a classic complication of long construct and deformity corrections. Iliac fixations have been extensively studied in the literature and have demonstrated superior biomechanical proprieties and lower complication rates. S2 alar iliac screws address the drawbacks of classical iliac screws but demonstrate similar biomechanical advantage. The main aim of this paper was to describe the S1 alar iliac (S1AI) screw fixation technique while evaluating our early results. S1AI screw fixation technique has the advantage of being able to achieve pelvic fixation without dissection to the S2 pedicle entry and is therefore a viable option for salvage of a failed S1 promontory screw.

Comparison Between S2-Alar-Iliac Screw Fixation and Iliac Screw Fixation in Adult Deformity Surgery: Reoperation Rates and Spinopelvic Parameters

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

The S2-alar-iliac (S2AI) technique has been described as an alternative method for pelvic fixation in place of iliac screws (ISs) in spinal deformity surgery. The objective of this study was to analyze the impact of S2AI screws on radiographical outcomes, including spinopelvic parameters.

METHODS

A retrospective review of 17 patients receiving ISs and 46 patients receiving S2AI screws for correction of adult spinal deformity between 2010 and 2015 with minimum 1-year follow-up was conducted. Patient data on postoperative complications, including reoperation rates and proximal junctional kyphosis (PJK), and radiographical parameters was collected and statistically analyzed.

RESULTS

With mean follow-up of 21.1 months, the overall reoperation rate was significantly lower in the S2AI group than in the IS group (21.7% vs 58.8%, P = .01), but the incidence of PJK was similar (32.6% vs 35.3%, P > .99). Moreover, the time to reoperation in the IS group was significantly shorter than in the S2AI group (P = .001), and the S2AI group trended toward a longer time to reoperation due to PJK (P = .08). There was a significantly higher change in pelvic incidence (PI) in the S2AI group (-6.0°) compared with the IS group (P = .001).

CONCLUSIONS

Compared with the IS technique, the S2AI technique demonstrated a lower rate of overall reoperation, a similar rate of PJK, longer time to reoperation, and possible reduction in PI. Future studies may be warranted to clarify the mechanism of these results and how they can be translated into improved patient care.

The Effects of Spinopelvic Parameters and Paraspinal Muscle Degeneration on S1 Screw Loosening

OBJECTIVE

To investigate risk factors for S1 screw loosening after lumbosacral fusion, including spinopelvic parameters and paraspinal muscles.

METHODS

We studied with 156 patients with degenerative lumbar disease who underwent lumbosacral interbody fusion and pedicle screw fixation including the level of L5-S1 between 2005 and 2012. The patients were divided into loosening and non-loosening groups. Screw loosening was defined as a halo sign larger than 1 mm around a screw. We checked cross sectional area of paraspinal muscles, mean signal intensity of the muscles on T2 weight MRI as a degree of fatty degeneration, spinopelvic parameters, bone mineral density, number of fusion level, and the characteristic of S1 screw.

RESULTS

Twenty seven patients showed S1 screw loosening, which is 24.4% of total. The mean duration for S1 screw loosening was 7.3±4.1 months after surgery. Statistically significant risk factors were increased age, poor BMD, 3 or more fusion levels (p<0.05). Among spinopelvic parameters, a high pelvic incidence (p<0.01), a greater difference between pelvic incidence and lumbar lordotic angle preoperatively (p<0.01) and postoperatively (p<0.05). Smaller cross-sectional area and high T2 signal intensity in both multifidus and erector spinae muscles were also significant muscular risk factors (p<0.05). Small converging angle (p<0.001) and short intraosseous length (p<0.05) of S1 screw were significant screw related risk factors (p<0.05).

CONCLUSION

In addition to well known risk factors, spinopelvic parameters and the degeneration of paraspinal muscles also showed significant effects on the S1 screw loosening.

The Fate of L5-S1 With Low-Dose BMP-2 and Pelvic Fixation, With or Without Interbody Fusion, in Adult Deformity Surgery

STUDY DESIGN

Retrospective comparative case series.

OBJECTIVE

Evaluate L5-S1 fusion rates when lower dose of bone morphogenic protein-2 (BMP-2) (average 3.2 mg) and pelvic fixation were used, with or without interbody fusion.

SUMMARY OF BACKGROUND DATA

Pseudarthrosis at L5-S1 is one of the most common complications of long fusions to the sacrum in adult deformity surgery. Strategies for decreasing pseudarthrosis include interbody fusion, use of BMP-2 at the lumbosacral junction, and the use of sacropelvic fixation, individually or in combination. High-dose BMP-2 (20-40 mg) placed posterolaterally has shown comparable fusion rates with interbody fusion.

METHODS

Retrospective review of 61 consecutive patients with minimum 2-year follow-up at a single institution. All patients had an isolated posterior approach, 5 or more levels fused including L5-S1, use of pelvic fixation, and no prior L5-S1 procedures. The patients were divided in 2 groups for comparison on the basis of the use of an interbody cage/fusion at the L5-S1 level. Revision rates and implant-related complications were also reported.

RESULTS

The fusion rate at L5-S1 was 97% (59/61), with no difference between the interbody and no interbody fusion groups (97% vs. 96%, P = 1.0). There were no significant differences in the radiographical parameters or deformity correction between the groups. The mean amount of BMP-2 used in the interbody group was 4.1 mg (2-10), 2.5 mg (0-8) in the disc space, and 1.6 mg (0-4) in the interbody cage, whereas there was no difference in the amount of recombinant human bone morphogenic protein-2 placed posterolaterally between the 2 groups (interbody fusion = 1.6 vs. non-interbody fusion = 2.0 mg, P = 0.08) along with autograft and allograft. The overall revision rate for L5-S1 nonunion was 1.6%.

CONCLUSION

The use of low dose of BMP-2 at the L5-S1 level in combination with sacropelvic fixation achieved satisfactory fusion rates in adult deformity surgery. No additional benefit was encountered by adding an interbody cage.

LEVEL OF EVIDENCE

4.