Coxa recta, coxa profunda and abductor ratio: hip morphology variants compared in an arthroplasty and control population.

Morphology variants of the hip such as coxa recta (aspherical femoral head and/or reduced head-neck concavity) or coxa profunda (overcoverage, or "deep" socket) are associated with cam and pincer impingement respectively, and may ultimately lead to coxarthrosis. Several population studies have documented the prevalence of hip morphotypes, but few studies have examined this prevalence in total hip arthroplasty (THA) patients, or persons without hip symptoms or signs. We reviewed whether coxa recta and profunda morphotypes were more prevalent in THA patients compared to normal controls. Further, we explored differences in hip abductor mechanism related to hip morphology. We examined 113 THA patients and 83 normal controls with anteroposterior pelvic and lateral hip radiographs. Coxa recta and profunda were classified with alpha and lateral CE-angle, respectively. The abductor ratio (AR) was measured on AP pelvic radiographs. Both coxa recta and profunda were more prevalent in THA patients than normal controls (coxa recta: male 42% vs 8%, female 15% vs 5%, respectively and coxa profunda: male 20% vs 1%, female 19% vs 6% respectively). AR was higher in females than males, both in THA patients (1.66 vs 1.47) and normal controls (1.68 vs 1,57). Coxa profunda was associated with a lower AR (1.54 vs 1.61). The higher prevalence of coxa recta and profunda in arthroplasty patients supports the theory of a role of these morphotypes in the development of coxarthrosis. The higher AR in females signifies the need for increased abductor work Coxa profunda may be an adaptation to lower the AR.