Surgical options for lumbosacral fusion: biomechanical stability, advantage, disadvantage and affecting factors in selecting options

An early experience of lumbopelvic fixation techniques at Alexandria University

Background

The aim of lumbopelvic fixation is to obtain a solid fusion across the lumbosacral junction. There are many indications for lumbopelvic fixation, namely, spinal deformity in cases requiring long segment fusion, pelvic obliquity, pseudarthrosis at the lumbosacral junction, infection or osteolytic tumors, and pathologic fractures. The classical iliac screws should be contained within the iliac bone but have some disadvantages: excessive soft tissue dissection needed for accurate insertion, screw prominence with patient discomfort, and usually, a side connector is needed to connect the iliac screws to the rest of the construct. Lumbopelvic fixation by insertion of S2 alar-iliac (S2AI) screws was recently described to overcome these disadvantages. In this study, the authors present the initial results for the evaluation of lumbopelvic fixation through the insertion of S2AI screws in 19 consecutive patients operated in the neurosurgery department at Alexandria University.

Objective

The aim of the study was to evaluate the efficacy and complications of lumbopelvic fixation through the use of S2 alar-iliac screws.

Methods

The authors conducted a retrospective cohort study of data collected from the database of patients who underwent lumbopelvic fixation through the insertion of S2AI screws from 2016 to 2019 at a single institution.

Results

There were 19 patients indicated for lumbopelvic fixation, operated by modern instrumentation systems using lumbar pedicle screws and S2 alar-iliac screws. There were 14 females and 5 males. The mean age at the time of the operation was 38.6 ± 19.4 years with a range from 11 to 65 years. There was a total of 37 S2AI screws, screw diameter was 7mm in all cases regardless of age, and the length of the screws ranged from 50 mm in a young female patient (11 years) to 90 mm in an old male patient (60 years). Two screws were inserted per patient except in one case with congenital scoliosis due to the bad bone quality and the multiple iatrogenic wrong paths. Postoperative VAS score for back pain was greatly improved in all patients after the first 6 months of follow-up from 8 ± 1.5 to 3.5 ± 1.2 (paired t-test = 11.182, P<0.001). All patients had a good spinal range of motion to maintain normal daily activities without any significant restrictions after the first 3 months of follow-up. Immediate postoperative radiological follow-up had revealed 2 cases of posterior pelvic breaches and one case with anterior pelvic breach but without clinical manifestations with no need for revision. Two cases of unilateral screw breakout were observed after the first 6 months of follow-up. Removal of screws after the first 6 months was done in one patient with spondylodiscitis due to the unresolved infection and screw pullout.

Conclusion

The insertion of S2AI screws is an effective technique for lumbopelvic fixation with a relatively low rate of complications. Pelvic breaches are the commonest complications encountered during the insertion of S2AI screws, although no significant clinical morbidities were reported.

Influence of Cage Design on Radiological and Clinical Outcomes in Dorsal Lumbar Spinal Fusions: A Comparison of Lordotic and Non-Lordotic Cages

Objectives

To evaluate the comparison between lordotic and non‐lordotic transforaminal lumbar interbody fusion (TLIF) cages in degenerative lumbar spine surgery and analyze radiological as well as clinical outcome parameters in long‐term follow up.

Methods

In a retrospective study design, we compared 37 patients with non‐lordotic cage (NL‐group) and 40 with a 5° lordotic cage (L‐group) implanted mono‐ or bi‐segmental in TLIF‐technique from 2013 to 2016 and analyzed radiological parameters of pre‐ and postoperative (Lumbar lordosis (LL), segmental lordosis (SL), and pelvic tilt (PT), as well as clinical parameters in a follow‐up physical examination using the Oswestry disability index (ODI), Roland–Morris Score (RMS), and visual analog scale (VAS).

Results

Surgery was mainly performed in lower lumbar spine with a peak in L4/5 (mono‐segmental) and L4 to S1 (bi‐segmental), long‐term follow‐up was on average 4 years postoperative. According to the literature, we found significantly better results in radiological outcome in the L‐group compared to the NL‐group: LL increased 6° in L‐group (51° preoperative to 57° postoperative) and decreased 1° in NL‐group (50° to 49° (P < 0.001). Regarding SL, we found an increase of 5° in L‐group (13° to 18°) and no difference in NL‐group (15°)(P < 0.001). In PT, we found a clear benefit with a decrease of 2° in L‐group (21° to 19°) and no difference in NL‐group (P = 0.008).

In direct group comparison, ODI in NL‐group was 23% vs 28% in L‐group (P = 0.25), RMS in NL‐group was 8 points vs 9 points in L‐group (P = 0.48), and VAS was in NL‐group 2.7 vs 3.2 in L‐group (P = 0.27) without significant differences.

However, the clinical outcome in multivariate analysis indicated a significant multivariate influence across ODI and RMS of BMI (Wilks λ = 0.57, F [4, 44] = 3.61, P = 0.012) and preoperative SS (Wilks λ = 0.66, F [4, 44] = 2.54, P = 0.048). Age, gender, cage type and postoperative PT had no significant influence (P > 0.05). Intraoperatively, we saw three dura injuries that could be sutured without problems and had no consequences for the patient. In the follow‐up, we did not find any material‐related problems, such as broken screws or cage loosening, also no pseudarthrosis.

Conclusion

In conclusion, we think it's not cage design but other influenceable factors such as correct indication and adequate decompression that lead to surgical success and the minimal difference in the LL therefore seemed to be of subordinate importance.

Bone Mineral Density Mapping of Iliosacral Region: The Use of Hounsfield Units to Optimize Transsacral Screw Trajectory

Introduction

Trauma, degenerative, pediatric, and neuromuscular deformities often require placement of implants into sacrum for construct stability. In these scenarios, fixation to the ilium is often added. To date, multiple studies have validated the correlation between Hounsfield units (HU) as measured on computed tomography and bone mineral density (BMD) on dual-energy X-ray absorptiometry to assess bone quality and fracture risk. We sought to map the BMD of the iliosacral region at the S1 and S2 levels using HU.

Materials and Methods

Pelvic CT scans of 100 patients were evaluated. HU measurements were taken from the anterior and posterior ilium, sacral ala, and sacral body using a best-fit circle encompassing a maximal amount of cancellous bone. Following the collection of all data points, an analysis of variance model was created to test the means and standard deviations of each anatomic region.

Results

The highest mean BMD was found in the following locations (in descending order): S1 sacral body (279.72 HU, 95% confidence interval [CI], 261.75–297.69), S1 anterior ilium (254.45 HU, 95% CI, 236.64–272.27), S2 anterior ilium (229.88 HU, 95% CI, 211.39–248.36), and the S2 sacral body (191.58 HU, 95% CI, 173.31–209.85). Comparing the anterior ilium to the sacral ala, there was a higher BMD measurement at both the S1 level by 151.7 HU (p &lt; 0.001) and the S2 level by 170.3 HU (p &lt; 0.001). The anterior ilium also showed a significantly higher BMD when compared to measurements taken at the posterior ilium at the same level: at the S1 level by 100.5 HU (p &lt; 0.001) and at the S2 level by 52.2 HU (p = 0.0006). The vertebral body had significantly higher mean BMD measurements when compared to the sacral ala at the S1 level by 176.9 HU (p &lt; 0.001) and at the S2 level by 131.95 HU (p &lt; 0.001).

Conclusions

The findings indicate that there is significantly higher BMD density of the anterior ilium and sacral body when compared to the sacral ala at both the S1 and S2 levels. In addition, the anterior ilium appears to provide more dense bone than the posterior ilium, as measured by mean HU.

The Effect and Safety of Polymethylmethacrylate-Augmented Sacral Pedicle Screws Applied in Osteoporotic Spine with Lumbosacral Degenerative Disease: A 2-Year Follow-up of 25 Patients

BACKGROUND

A high rate of instrumentation failure is frequently seen in osteoporotic spines, especially at the sacral segment because of the great shear stress. Several techniques of sacral pedicle screw placement, such as bicortical and tricortical fixation, have been developed; however, the problems of loosening and pulling out of the screws are still a concern. Recently, the polymethylmethacrylate (PMMA)-augmented pedicle screws have been shown to strengthen the purchase in osteoporotic spine, but there are few reports on the effect of S1 pedicle screw with PMMA augmentation.

METHODS

Seventy-five patients receiving cement-augmented pedicle screws at lumbosacral vertebra were enrolled and divided into 3 groups by different patterns of S1 pedicle screw placement: S1 pedicle screw with PMMA augmentation (group A, 25 patients), S1 bicortical pedicle screw fixation (group B, 25 patients), and S1 tricortical pedicle screw fixation (group C, 25 patients). The Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) scores were assessed preoperatively and at the last follow-up. Besides, the complications, loosening rate, and fusion rate were recorded.

RESULTS

The VAS and ODI scores at the last follow-up were significantly improved in the 3 groups compared with preoperative results. Better pain relief and functional improvement at the last follow-up was seen in group A compared with the other 2 groups; however, no significant difference was detected between groups B and C. Although the lowest screws loosening rates and the highest fusion rate were found in group A, no significant difference among these 3 groups. Furthermore, longer fusion segments and larger postoperative pelvic incidence-lumbar lordosis (PL-LL) were found as risks related to S1 screw loosening without cement augmentation.

CONCLUSIONS

The S1 pedicle screws with PMMA augmentation achieved better stability with less screw loosening in the osteoporotic spine with lumbosacral degenerative diseases compared with bicortical/tricortical fixation at S1. This procedure is especially recommended for patients with long segment fixation and large postoperative PI-LL, but there is also a risk of bone cement leakage and a learning curve.

Analysis of the s2 alar-iliac screw as compared with the traditional iliac screw: does it increase stability with sacroiliac fixation of the spine?

BACKGROUND CONTEXT

Arthrodesis of the lumbosacral junction continues to be a challenge in pediatric and adult spinal deformity surgery.

PURPOSE

To evaluate the biomechanical rigidity of two types of lumbosacral fixation. Our hypothesis was that the use of S2 alar-iliac (S2AI) fixation will result in statistically similar biomechanical fixation as compared with use of an iliac screw with a 95% confidence interval.

STUDY SETTING

Controlled biomechanical laboratory METHODS: Ten human cadaveric lumbosacral specimens were separated into two test groups: (1) S2AI (n=5) and (2) iliac screw (n=5). S2AI and iliac screws were placed according to current clinical practice techniques. Specimens were mounted in an unconstrained dual leg stance configuration for testing in flexion, extension, lateral bending, and axial rotation. These loads were induced by moving the offset loading arm 10 mm in the respective direction from the point of neutral motion with displacement control up to a 10 N-m moment, except axial rotation which used a 4 N-m moment. Optical tracking was used to monitor motion of the vertebra, pelvis, and fixation instrumentation during testing. Specimens were tested in intact and instrumented states. The stiffness values between S2AI and iliac screw configurations were compared.

DISCLOSURE

The present study received external research support (>$50,000 -<$75,000) from Stryker Spine (Allendale, NJ, USA).

RESULTS

There was a consistent trend of increased construct stiffness for all S2AI samples compared with the iliac screw group. However, none of the groups tested reached statistical significance for a 95% confidence interval.

CONCLUSIONS

S2AI screws are just as stable as iliac screws with biomechanical testing in flexion, extension, rotation, lateral bending, and axial rotation. Given the similarities of biomechanical testing to human movements, these findings support S2AI screws as a viable option for lumbosacral fixation.