Risk Factors for Operative Adjacent Segment Disease Following Laminectomy Without Fusion for Lumbar Spinal Stenosis

BACKGROUND AND OBJECTIVES: Adjacent segment disease (ASD) generally refers to the development of symptomatic degenerative changes at a level neighboring a fusion. ASD is often attributed to alteration in the native biomechanics of the spine secondary to elimination of a motion segment and is widely cited as a risk of lumbar fusion operations. However, the development of ASD may also represent a product of the normal aging process. We sought to identify the incidence of ASD following decompressive nonfusion procedures in lumbar stenosis. METHODS: We retrospectively identified all adult patients undergoing open laminectomy for lumbar stenosis over a 6-year period at an academic center. Patients undergoing fusion, diskectomy, >4 level procedures, or those with a fusion adjacent to the operative segment were excluded. The primary end point was the incidence of clinical and radiographic ASD requiring reoperation at a level immediately rostral or caudal to the operative segment. A secondary end point was identification of clinical and radiographic risk factors for the development of ASD, based on a multivariate Cox proportional hazards model. RESULTS: We identified 658 patients meeting all inclusion and exclusion criteria for analysis. Over a mean clinical follow-up period of 32 months, 62 (9.4%) patients underwent reoperation for ASD. The ASD reoperation occurred at a mean of 29.8 months after initial laminectomy. Factors associated with development of ASD on multivariate analysis were a history of cervical/thoracic spine surgery, lumbar spine surgery, or joint arthroplasty (shoulder, knee, and/or hip) prior to the index laminectomy. CONCLUSION: In this cohort analysis of patients undergoing laminectomy without fusion, we found an incidence of ASD of nearly 10%. This provides evidence that the normal degenerative process-together with impact from prior surgery-likely contributes to the development of ASD, although the specific amount by which fusion accelerates this process is yet to be quantified.