Suboccipital muscle morphology and upper cervical alignment in atlantoaxial dislocation: a cross-sectional MRI study

To examine whether magnetic resonance imaging-derived suboccipital muscle morphology is associated with neutral and position-related upper cervical alignment in adults with atlantoaxial dislocation.

This retrospective cross-sectional study included 64 patients. Relative cross-sectional area (RCSA) and fat infiltration (FI) were measured for the obliquus capitis inferior (OCI) and for a combined posterior group comprising the rectus capitis posterior major, semispinalis capitis, and splenius capitis. The atlantodental interval (ADI) and C1-C2 and C0-C2 Cobb angles were measured on neutral, flexion, and extension radiographs. Pearson correlations were evaluated across four muscle metrics and nine alignment outcomes, with Holm adjustment across all 36 tests.

Lower OCI RCSA was associated with a larger neutral ADI (r = -0.434; P＜0.05) and smaller neutral C1-C2 (r = 0.451; P＜0.01) and neutral C0-C2 (r = 0 .470; P＜0.01) Cobb angles. Higher OCI FI showed the opposite pattern (r = 0.705, -0.517, and - 0.400; P < 0.01, < 0.01, and＜0.05, respectively). Associations involving the combined posterior group and all position-related excursions were not significant after multiplicity correction.

OCI morphology was associated with neutral upper cervical alignment, but not with position-related excursion after family-wise error control. These unadjusted cross-sectional associations do not establish directionality or support using muscle measurements to guide fixation or nonoperative treatment.