Interspinous Process Fixation versus Pedicle Screw Fixation in ALIF/LLIF: 2-year Outcomes from a Prospective Randomized Multi-Center Trial

Presented at SMISS Annual Forum 2016
By Kee Kim MD
With Peter Passias MD, Ryan DenHaese MD, Clint Hill MD, K. Brandon Strenge MD, Alexandre de Moura MD, Chris Ferry MS, Brieta Bejin MS, Kim Martin PhD, Sarah Martineck PA, Tom Glorioso MS, Paul Arnold MD, Ripul Panchal DO,

Disclosures: Kee Kim MD A; Lanx Inc., B; Zimmer Biomet Spine. Peter Passias MD B; Medicrea., Ryan DenHaese MD B; Zimmer Biomet Spine. E; Zimmer Biomet Spine., Clint Hill MD B; Zimmer Biomet Spine., K. Strenge MD B; Zimmer Biomet Spine., Alexandre de Moura MD None, Chris Ferry MS E; Zimmer Biomet Spine., Brieta Bejin MS E; Zimmer Biomet Spine. , Kim Martin PhD E; Zimmer Biomet Spine., Sarah Martineck PA B; Zimmer Biomet Spine., Tom Glorioso MS B; Zimmer Biomet Spine., Paul Arnold MD None, Ripul Panchal DO B; Zimmer Biomet Spine.,

Introduction

Rigid interspinous process fixation (ISPF) has garnered consideration as a less disruptive alternative to pedicle screw fixation (PSF) when supplementing spinal arthrodesis; however, it remains largely unknown whether ISPF can provide the biomechanical rigidity necessary to support the quality and longevity of outcomes observed with PSF. To date, no study has provided Level I evidence regarding the efficacy of ISPF. 

Aims/Objectives

The objective of this study was to prospectively compare the outcomes of subjects receiving circumferential spinal arthrodesis with adjunctive ISPF or PSF. 

Methods

This was a prospective, randomized, controlled, multi-center (11 investigators), non-inferiority trial to assess ISPF and PSF in anterior (ALIF) and lateral (LLIF) interbody fusion. All subjects received single-level interbody fusion with supplemental ISPF (n=66) or PSF (n=37) for the treatment of degenerative disc disease and/or spondylolisthesis (Grade ≤ 2). The randomization ratio was 2:1, ISPF (Aspen MIS Fusion System, Zimmer Biomet Spine) to PSF subjects. The PSF approach (MIS/open; unil/bilateral) and interbody approach (ALIF or LLIF) were per investigator institutional standard-of-care. Perioperative outcomes, patient reported outcomes, and fusion outcomes were collected through 24months. Analysis was performed using a linear mixed model (p<0.05). 

Results

No statistically significant differences were observed between cohorts with respect to change in patient reported outcome scores (ODI, SF-36, ZCQ) from baseline to 1.5, 3, 6, 12, or 24mos. Mean ODI score improvement at 12mos/24mos was 26.5/23.3 and 23.2/23.1 for ISPF and PSF subjects, respectively. The difference in ODI improvement of +3.3pts at 12mos exceeded the established non-inferiority margin of 10pts. Radiographic fusion success was (score of BSF-3) ISPF - 94.9% and PSF - 85.0%, respectively. At 24mos, 3 ISPF subjects (3%) and 2 PSF subjects (5.4%) had undergone a secondary procedure in which the posterior instrumentation was revised or explanted. 

Conclusions

A/LLIF with ISPF supported robust improvement in pain/satisfaction while achieving excellent interbody fusion success. Outcomes with ISPF were comparable/favorable to those achieved with PSF, indicating that ISPF is a clinically effective alternative when supplementing single-level arthrodesis. Given the minimal disruption needed to achieve ISPF, the technique complements well with the biomechanically robust nature of A/LLIF.