Preoperative longus colli functional cross-sectional area is associated with postoperative C2–C7 sagittal vertical axis change after laminectomy and fusion for degenerative cervical myelopathy

To determine whether preoperative morphometric parameters of the longus colli (LC) are associated with postoperative sagittal alignment and functional recovery after laminectomy and fusion (LF). A total of 168 patients with degenerative cervical myelopathy (DCM; mean age, 59.2 years) who underwent C3–C6 LF and completed a minimum 24-month follow-up were retrospectively analyzed. According to the change in C2–C7 sagittal vertical axis (ΔcSVA), patients were categorized into cSVA decrease (ΔcSVA ≤ − 10 mm, n = 25), cSVA stable (− 10 mm < ΔcSVA ≤ 10 mm, n = 95), and cSVA increase (ΔcSVA > 10 mm, n = 48) groups. Preoperative axial T2-weighted MRI at the C3–C4, C4–C5, and C5–C6 disc levels was used to measure LC cross-sectional area (CSA), fatty infiltration (FI), functional CSA (FCSA), and asymmetry index. Clinical scores (NDI, VAS, and mJOA) and sagittal radiographic parameters were compared among the groups. Significant intergroup differences in LC parameters were observed only at the C5–C6 level. At this level, the cSVA increase group showed greater FI and lower CSA and FCSA than the cSVA decrease and cSVA stable groups ( P < 0.05). Partial correlation analysis showed that C5–C6 FCSA was negatively correlated with ΔcSVA ( r = − 0.547), ΔNDI ( r = − 0.473), and ΔVAS ( r = − 0.400) (all P < 0.05). In multiple linear regression, lower C5–C6 FCSA was independently associated with greater ΔcSVA (β = −0.549, P < 0.05). Receiver operating characteristic analysis for postoperative cSVA increase (ΔcSVA > 10 mm) yielded an area under the curve of 0.759 (95% CI, 0.676–0.834), with a cohort-specific exploratory FCSA cutoff of 98.3 mm² (sensitivity, 81.3%; specificity, 64.2%). LC parameters at C3–C4 and C4–C5 were not significantly associated with ΔcSVA. Lower preoperative C5–C6 LC FCSA was independently associated with greater postoperative cSVA increase after LF for DCM. This level-specific association should be considered exploratory and requires further prospective and biomechanical validation.