Introduction: Lumbar stenosis is a common spinal pathology and studies have shown that surgical treatment is often more effective than non-operative management. Surgical options for the treatment of lumbar stenosis include decompression alone or decompression with fusion. Patients are often chosen for decompression with fusion when there is perceived instability; however, it is often unclear which radiographic parameters indicate instability requiring fusion. The aim of the current study was to evaluate the changes in radiographic motion metrics as well as pain NRS scores in patients with lumbar stenosis and spondylolisthesis undergoing decompression and fusion. We hypothesize that patients will improve in various intersegmental motion metrics and some will relate to improved post-operative pain NRS scores following decompression and fusion.

Methods: This was a retrospective single center cohort study. Patients treated for single level lumbar stenosis with spondylolisthesis by decompression plus fusion were included. preliminary analysis includes 23 patients. Pre-op and 1-year post-op flexion/extension X-ray images were analyzed with previously validated motion analysis software. Since the mechanical integrity of soft-tissues cannot be assessed unless the soft-tissues are sufficiently stressed, patients with <3 deg of pre-op intervertebral rotation between flexion and extension were excluded. Demographic data were obtained from medical records, including age, gender, length of stay, comorbidities and pain NRS scores. Outcome measures included Pain NRS scores, Angular Motion, Intervertebral Translation, Sagittal Plane Shear Index (SPSI), Spondylolisthesis Index, Anterior and Posterior Disc Integrity Index, Global ROM.

Results: Of the 23 patients, 14 (61%) were female and 9 (39%) were male. Ages ranged from 28 to 77 years old with an average of 61 at the time of surgery. Three patients had surgery at L3-L4 (13%), 19 had surgery at L4-L5 (83%), and one had surgery at L5-S1 (4%). All 23 patients received decompression with fusion. The 95% confidence interval of a dataset that includes 384 radiographically normal asymptomatic volunteers was used to define normal limits of motion. SPSI > 2 indicates that the translation per degree of rotation was beyond the upper limit of normal. The mean pre-op SPSI at the treatment level was 1.4±2.2 [-3 to 6.4] with 13 subjects having <2 and 9 subjects having >2. Patients with a normal pre-operative SPSI had a statistically significant improvement in pain NRS scores (6.7±1.7 to 1.8±2.3; p < 0.001) while patients with abnormal pre-op SPSI did not have a statistically significant improvement in pain NRS scores (5.1±2.0 to 3.5±2.5; p = 0.160)

Discussion: SPSI is an objective measure of sagittal plane instability that may inform physicians of the need for fusion in patients undergoing fusion for spondylolisthesis with spinal stenosis. A normal pre-operative SPSI was associated with a clinically significant improvement in post-op pain NRS scores at one year while patients with an abnormal SPSI did not have statistically significant improvements.