Predictive value of preoperative T1 slope minus cervical lordosis for clinical outcomes after standalone laminectomy in elderly degenerative cervical myelopathy

Standalone cervical laminectomy is frequently performed in elderly patients with degenerative cervical myelopathy (DCM), yet practical prognostic determinants remain limited. We examined whether the preoperative T1 slope minus cervical lordosis (T1S-CL) predicts 2-year clinical outcomes and yields clinically useful decision thresholds. In this retrospective cohort of elderly DCM patients who underwent multilevel standalone laminectomy with a minimum 2-year follow-up, outcomes were assessed using the modified Japanese Orthopaedic Association (mJOA) score and Visual Analog Scale (VAS) for neck and arm pain. The primary endpoint was achievement of the minimal clinically important difference (MCID), prespecified as a ≥ 2-point increase in mJOA. Cervical alignment parameters including T1 slope (T1S), C2-C7 lordosis (CL), and T1S-CL were measured pre- and postoperatively. Predictive performance was evaluated using receiver operating characteristic (ROC) analysis and multivariable logistic regression with internal bootstrap validation. Among 68 patients (mean age 68.38 ± 3.15 years), 82.4% achieved MCID at 2 years. Laminectomy was associated with a modest decline in lordosis, and a corresponding increase in T1S-CL. Preoperative T1S-CL independently predicted MCID achievement (adjusted odds ratio per 1° = 0.556; p < 0.001) and demonstrated superior discrimination compared with T1S or CL alone. A two-threshold strategy emerged: T1S-CL ≤ 16.5° showed high specificity (91.7%) and positive predictive value (97.2%) for favourable outcome, whereas T1S-CL > 20° provided strong sensitivity (94.6%) for identifying poor outcome. These findings support T1S-CL as a promising preoperative predictor for exploratory risk stratification. However, the proposed thresholds require external validation before routine clinical use.