Limited Improvement with Minimally Invasive Lumbar Decompression Alone for Degenerative Scoliosis with Cobb Angle over 20 Degrees: The Impact of Decompression Location.

STUDY DESIGN:Retrospective review of a prospectively collected multi-surgeon registry. OBJECTIVE:To evaluate the outcomes of minimally invasive (MI) decompression in patients with severe degenerative scoliosis (DS) and identify factors associated with poorer outcomes. SUMMARY OF BACKGROUND CONTEXT:MI decompression has gained widespread acceptance as a treatment option for patients with lumbar canal stenosis and DS. However, there is a lack of research regarding the clinical outcomes and the impact of MI decompression location in patients with severe DS exhibiting a Cobb angle exceeding 20 degrees. MATERIALS AND METHODS:Patients who underwent MI decompression alone were included and categorized into the DS or control groups based on Cobb angle (>20 degrees). Decompression location was labeled as "scoliosis-related" when the decompression levels were across or between end vertebrae, and "outside" when the operative levels did not include the end vertebrae. The outcomes including Oswestry Disability Index (ODI) were compared between the propensity score-matched groups for improvement and minimal clinical importance difference (MCID) achievement at ≥1 year postoperatively. Multivariable regression analysis was conducted to identify factors contributing to the non-achievement of MCID in ODI of the DS group at the ≥1 year timepoint. RESULTS:A total of 253 patients (41 DS) were included in the study. Following matching for age, gender, osteoporosis status, psoas muscle area, and preoperative ODI, the DS groups exhibited a significantly lower rate of MCID achievement in ODI (DS: 45.5% vs. control 69.0%, P=0.047). The "scoliosis-related" decompression (Odds ratio: 9.9, P=0.028) was an independent factor of non-achievement of MCID in ODI within the DS group. CONCLUSION:In patients with a Cobb angle>20 degrees, lumbar decompression surgery, even in the MI approach, may result in limited improvement of disability and physical function. Caution should be exercised when determining a surgical plan, especially when decompression involves the level between or across the end vertebrae. LEVEL OF EVIDENCE:3.