The Influence of Spinous Process Union on Clinical Outcomes After Spinous Process Osteotomy for Lumbar Spinal Stenosis After 2 Years: A Secondary Analysis From the NORDSTEN-Study.

Background: Lumbar spinal stenosis is a prevalent and increasingly important cause of low back pain, leg pain, and walking impairment. Minimally invasive decompressive techniques such as spinous process (SP) osteotomy have become more common in recent years. The main aim of this study was to investigate the proportion of complete SP union and whether complete radiological healing after the osteotomy is associated with superior clinical outcome after 2 years.

Methods: In this retrospective cohort study, 149 patients were included from the Spinal Stenosis Trial, a part of the NORwegian Degenerative spondylolisthesis and spinal STENosis study. Computed tomography imaging was performed 2 years postoperatively. The number of osteotomies and the number of SP unions were recorded. Patients were divided into groups based on the degree of union: nonunion, partial union, and complete union. Rate of success (>30% improvement in Oswestry Disability Index [ODI]) and mean change in ODI were the primary outcome measures. We compared the differences between baseline and follow-up between the Degree of Union groups.

Results: The study included 102 of 149 eligible patients. Ten patients (9.8%) were classified as having nonunion, 15 (14.7%) as having partial union, and 77 (75.5%) as having complete union. Of the 155 osteotomies, there were 122 classified as union (77%). The success rate was 74%, with no influence of SP union. The mean change in the ODI was -20.1 (95% CI -37.0, 14.2) with no influence of SP union.

Conclusions: We found no influence of SP union, classified by computed tomography, on clinical outcome 2 years after SP osteotomy in patients with lumbar spinal stenosis.

Clinical relevance: Supplying useful information about SPO to assist surgeons in the choice of decompressive technique.

Level of evidence: 2: