Radiographic and Clinical Outcomes at 1-year after Spinous Process Fixation and PLF in an Elderly Population

Presented at SMISS Annual Forum 2014
By Robert Tatsumi MD
With

Disclosures: Robert Tatsumi MD A; Lanx, B; Lanx, C; Lanx, F; Lanx

Introduction:
Interspinous process fixation (ISPF) for lumbar fusion has gained attention as a less invasive option for patients undergoing PLF for the treatment of degenerative disc disease, spinal stenosis, spondylolisthesis, and/or instability of the lumbar spine. Minimally invasive techniques have become of particular interest in the elderly population.

Aims/Objectives:
Our hypothesis in this retrospective cohort study was that elderly patients undergoing decompression and posterior fusion with ISPF would have clinically (minimum 15 point improvement, as defined in the literature as the clinically important difference) and statistically significant improvement in disability as measured by Oswestry Disability Index (ODI). Our secondary hypothesis was that posterior fusion rates with ISPF would be comparable to published rates for pedicle screw fixation (PSF).

Methods:
64 consecutive patients, from 10/2009 to 12/2012, who had decompression with PLF facilitated by an ISPF device (Biomet Spine, LLC. (by its subsidiary Lanx, Inc.)), were reviewed. Those patients with at least 1-year follow up, with 1-level SPF for PLF, were included in this study. Baseline and post-operative ODI scores were collected, as well as diagnosis, smoking status, and demographic data. A paired t-test with a type I error rate of 0.05 was performed to evaluate if ODI scores were reduced from baseline at 1-year and 2-years after surgery. Facet fusion and interlaminar posterior fusion rates were examined via upright, neutral and lateral, flexion and extension radiographs. Lenke criteria and <2mm of motion were used to assess PLF.

Results:
37 patients had baseline and 1-year ODI scores. 23 patients had baseline and 2-year ODI scores. Fusion data was available on 31 patients at 1-year and 20 patients at 2-years. All patients had a diagnosis of degenerative spondylolisthesis. The mean patient age was 71.3 years (SD=10.1). 51.6% of the patients were female. Mean baseline ODI was 50.9 (SD=12.3). Mean 1-year ODI was significantly reduced by 24.7 points (95% CI=18.3-31.10, p=<0.0001) from baseline and by 28.2 points (95% CI=20.4-35.9, p=<0.0001) at 2 years. Facet fusion rate at 1-year at 2-years was 90.3% and 90.0% respectively. Posterior/interlaminar fusion rate was 83.9% at 1-year and 80.0% at 2-years. These fusion rates compare well to a recent meta-analysis of posterior fusion rates with PSF, which showed an average of 86% fusion in 124 patients across three studies.

Conclusions:
In this elderly cohort, ISP fixation results in clinically and statistically significant improvement in ODI scores with a fusion rate comparable to rates previously published for PSF