Alpha Angle and Anterior Femoral Neck Offset Identify Different Cohorts of Cam Morphology: An Osteologic Study.

Purpose: To explore differences in cam morphology defined by alpha angle (AA) and anterior femoral neck offset (AFNO) in the context of other anthropometric parameters in an osteologic collection to further elucidate whether each measurement tool is identifying the same underlying pathology.

Methods: Anthropometric measurements of 992 cadaveric hips from the Hamann-Todd Osteological Collection were analyzed. Femurs with cam morphology were identified by AA >55° or AFNO <7 mm. Anthropometric parameters stratified by cam morphology were assessed with Wilcoxon rank-sum and Pearson χ² tests. Multivariate logistic regressions were performed on significant variables in univariate analysis to examine the predictive ability of anthropometric variables to cam morphology.

Results: Cam morphology was identified in 242 hips via AA, 344 hips via AFNO, and 123 hips via both measures. Multivariate logarithmic regression analysis demonstrated that sex negatively predicted AA (females with less pathology, β = -0.14, P = .04), race negatively predicted AA (Blacks with less pathology, β = -0.21, P < .01), and proximal femoral osteoarthritis was positively associated with AA (β = 0.16, P = .02), while none of these were associated with AFNO. On the other hand, right-side specimens were associated with AA (β = 0.15, P = .02) and AFNO (β = 0.25, P < .01), whereas the combined version was unassociated with both measures.

Conclusions: In conclusion, cam morphology was identified in a modest percentage of osteologic specimens by both AA and AFNO in our study. Further, associations of multiple demographic, anthropometric, and anatomical parameters to AA and AFNO suggest they may identify different subsets of cam morphology.

Clinical relevance: Cam morphology identified by AA versus AFNO may represent 2 different pathologic entities. Future studies should assess differences between these measures in a clinical cohort and determine whether these 2 definitions of cam morphology identify different clinical populations.