Gender-specific patterns of external occipital protuberance hyperplasia: associations with nuchal ligament ossification and cervical sagittal imbalance in myelopathy patients.

Abstract

Study design: Retrospective cross-sectional analysis of 187 consecutive patients undergoing surgical treatment for cervical spondylotic myelopathy (CSM).

Purpose: To investigate sexual dimorphism in external occipital protuberance (EOP) hyperplasia morphology and elucidate its clinical correlation with ossification of the nuchal ligament (ONL) and cervical sagittal imbalance.

Overview of literature: Emerging evidence implicates EOP hyperplasia as potential biomarker of chronic neck strain, yet its relationship with ONL and cervical sagittal imbalance remains underexplored in surgical CSM cohorts.

Methods: Cervical radiographs were analyzed. EOP hyperplasia was classified into three subtypes with standardized length measurements. Variables encompassed demographics, ONL-related indices, and sagittal parameters. Subtype comparisons and multivariate regression analyses (with EOP length as dependent variable) were conducted.

Results: Analysis of 187 CSM patients (64.2% male) identified gender-specific patterns: males exhibited greater EOP length (9.4±6.8 mm vs. 4.6±3.4 mm, p<0.001). Type III EOP demonstrated male predominance (82.4% vs. type I 31.8%, type II 51.4%; p<0.001), with associated longer hyperplasia length (11.6±6.6 mm vs. type II 5.1±1.9 mm, p<0.001). Type III EOP was associated with higher ONL prevalence (type III 64.8% vs. type I 45.5%, type II 41.9%; p=0.010) and longer ONL osteophyte length (type III 18.8±9.8 mm vs. type I 14.2±8.1 mm, type II 14.2±9.4 mm; p=0.046). Multivariate regression confirmed male sex (β=-3.82, p=0.009), ONL osteophyte length (β=0.16, p=0.017), T1 slope (β=0.27, p=0.041), and spino-cranial angle (β=-0.19, p=0.009) as factors independently associated with EOP length (adjusted R²=0.382).

Conclusions: Severe EOP hyperplasia exhibits a male-predominant distribution pattern and demonstrates significant radiological associations with ONL and cervical sagittal imbalance in CSM patients. These findings advocate for EOP evaluation in clinical evaluations to identify high-risk biomechanical profiles.