Should BMI influence anterior versus posterior approach surgery in patients with CSM? A 5-year Spine CORe™ analysis of QOD data

OBJECTIVE: Cervical spondylotic myelopathy (CSM) is a common cause of spinal cord dysfunction worldwide and can be treated through anterior or posterior approaches. Both strategies achieve acceptable results, but the growing prevalence of obesity poses unique challenges. Data directly comparing outcomes across body mass index (BMI) strata are limited. Here, the authors examined rates of achieving minimal clinically important differences (MCIDs) in patient-reported outcomes (PROs) between anterior and posterior approaches relative to BMI. METHODS: This was a post hoc analysis of prospectively collected data from the 14-site Spine CORe™ study group of the Quality Outcomes Database (QOD). Baseline data and PROs-including numeric rating scale (NRS) neck and arm pain, Neck Disability Index (NDI), EQ-5D, and modified Japanese Orthopaedic Association (mJOA) scores-were collected through 60 months. Patients were stratified by an a priori BMI threshold of 30 kg/m2 and by surgical approach (anterior vs posterior). Multivariable regression was used to compare achievement of MCID across approaches within each BMI group. In parallel, unsupervised clustering of baseline-adjusted PROs was combined with a doubly robust estimation framework to assess approach-specific probabilities of achieving optimal outcomes across the continuous BMI spectrum. RESULTS: Among 1085 patients, 759 (70.0%) underwent anterior and 326 (30.0%) underwent posterior surgery. Anterior approaches were associated with shorter length of stay and fewer nonhome discharges (p < 0.001). For patients with BMI < 30 kg/m2, anterior surgery conferred higher odds of achieving MCID in NRS arm pain (OR 0.45, p = 0.032). For those with BMI ≥ 30 kg/m2, anterior surgery was associated with greater odds of achieving MCID in mJOA (OR 0.32, p = 0.007) and NDI (OR 0.42, p = 0.031) scores. The results were consistent in sensitivity analyses. The doubly robust model identified a BMI range of 29.1-36.7 kg/m2, where anterior approaches significantly increased the probability of optimal outcomes (risk difference > 8.1%; lower confidence interval > 0). Anterior approaches also demonstrated greater probability of achieving optimal outcomes at higher BMIs, though without statistical significance. CONCLUSIONS: For BMI < 30 kg/m2, both approaches improved disability and quality of life, with anterior surgery offering added relief of arm pain. For BMI ≥ 30 kg/m2, anterior surgery provided superior functional and disability outcomes. Most importantly, anterior surgery became significantly more advantageous beginning at BMI 29.1 kg/m2. However, approach selection remains multifactorial, as anterior and posterior cohorts differed in mean age (anterior 58.7 vs posterior 64.5 years) and mean operated levels (anterior 1.9 vs posterior 4.2 levels). While anterior approaches may be most commonly employed for younger patients or for one- and two-level pathology, posterior approaches remain an important option for multilevel cervical stenosis or in the elderly to avoid dysphagia. Thus, this study highlights BMI as just one of many key factors in approach selection for CSM, but should not replace individualized clinical decision-making.