Background: The presence of acetabular dysplasia or femoro-acetabular impingement increases the chance of an earlier total hip arthroplasty (THA). Surprisingly, the influence of femoral and acetabular parameters on the age at which THA is required remains poorly investigated. The aim of this study was to evaluate the radiographic hip morphotype at the time of THA using an artificial intelligence-based analysis to assess potential differences.

Methods: Overall, 6,767 patients (mean age 66 years [range, 16 to 99]; women: 60.6%; men: 39.4%) from a single orthopaedic center were included in the final analysis. Images were analyzed using artificial intelligence-powered software. The lateral-center-edge angle and the neck-shaft angle (caput-collum-diaphyseal) were used to determine the nine different hip morphotypes based on the coronal plane alignment of the hip (CPAH, I to IX).

Results: Patients who had valgus-aligned femoral necks (CPAH, I, IV, and VII) were significantly younger at the time of THA compared to patients who had femoral varus necks (CPAH, III, VI, and IX), suggesting a potential negative effect of valgus and a protective effect of varus alignment independent of acetabular coverage. Type I hips, defined as acetabular undercoverage in combination with femoral valgus alignment, were on average 16.2 years younger at the time of THA compared to type IX hips with acetabular overcoverage and varus alignment.

Conclusions: The hip morphotype had a major impact on the timing of THA. Femoral varus neck alignment demonstrated a protective effect across all age groups, whereas acetabular undercoverage and femoral valgus necks were associated with an earlier need for THA.