Does Iliac Screw Fixation Reduce L5-S1 Non-unions?

2019

Summary

The strong advocacy for sacropelvic fixation is largely based on biomechanical studies and short-term clinical studies. This study is the largest prospectively collected data series examining the long-term clinical benefits of iliac screw fixation. This study demonstrates that iliac screw fixation promotes lumbosacral arthrodesis while contributing to proximal junctional kyphosis.

Hypothesis

Iliac screw fixation reduces the rate of lumbosacral non-unions in long posterior spinal fusion constructs.

Design

Retrospective cohort study of prospectively collected data from a single surgical spine practice.

Introduction

Sacropelvic fixation (SPF) is strongly advocated in long deformity constructs to reduce the cantilever forces seen by S1 screws and promote fusion. Much of the data demonstrating the protective effects of SPF are largely based on cadaveric biomechanical studies. Previous clinical studies advocating the benefits of iliac screw fixation (ISF) are limited by short term follow-up. This study will compare nonunion rates and the 5yr clinical and radiographic outcomes between deformity constructs with ISF vs. posterior spinal fusion (PSF) alone.

Methods

115 consecutive adult spinal deformity patients who underwent at minimum T10-pelvis PSF and had 5yr follow-up were included. Two cohorts were compared: 1) No iliac fixation (PSF; n=27) and 2) Iliac screw fixation (ISF; n=88). Additionally, sub-groups were created based on fusion technique: A) Interbody support (IB) w/ISF (n=65) B) PSF w/ISF (n=23) C) IB w/o ISF (n=24) D) PSF alone (n=3). Radiographic measurements and clinical outcome measures (VAS, ODI) were compared preop, postop and at 5 years.

Results

There were no differences in baseline patient characteristics between cohorts. L5-S1 non-union occurred more frequently in the group without iliac fusion, regardless of whether interbody fusion was used or not (PSF: n=5, ISF: n=1, p=0.002). Proximal junctional kyphosis (PJK) occurred more commonly in constructs with ISF (A:9, B:7, C:1, D:2, p=0.009) with some requiring revision surgery (A:6, B:6, C:0, D:0, p=0.026). No significant differences in other complications between cohorts or sub-groups. At final follow-up there were no significant differences in VAS or ODI between cohorts; all cohorts had improvement from baseline scores.

Conclusion

5yr clinical outcomes demonstrate that ISF promotes arthrodesis at the lumbosacral junction in adult deformity patients undergoing instrumented long PSF. However, ISF may lead to higher rates of PJK and PJF requiring revision surgery.