Definition of Femoral Morphotypes Based on the Coronal Plane Alignment of the Hip Classification

BACKGROUND: In total hip arthroplasty (THA), accurate reconstruction of physiological joint biomechanics is determined by the individual patient's proximal femoral anatomy and stem design. Previous studies demonstrated a wide variation of femoral canal shapes and an association with extramedullary geometrical features. The purpose of this study was to propose a comprehensive classification for the coronal plane alignment of the hip (CPAH) that incorporates intramedullary and extramedullary parameters. We sought to determine the distribution of femoral morphotypes in an osteoarthritic cohort and to assess the reconstructive potential of four common femoral stem designs in each CPAH type. METHODS: The preoperative radiographs of 2,345 patients undergoing primary uncemented THA were retrospectively analyzed, including Dorr classification, neck-shaft angle (NSA), femoral offset (FO), and femoral offset ratio (FOR). The CPAH classification defines nine morphotypes based on the combination of Dorr type and NSA. Each morphotype is categorized into a normal- and a high-offset subgroup. Digital templating was conducted to assess the reconstruction of FO, leg length (LL), and the agreement between anatomy and stem geometry. RESULTS: The CPAH types 2N, 5N, 5H, 6N, and 8N accounted for a combined percentage of 82% (n = 1,928), whereas the remaining morphotypes represented less common anatomical constitutions. Canal shape, FO, and NSA were associated with demographic characteristics (age, P < 0.001; sex, P < 0.001). Subgroup analyses stratified by CPAH types revealed that the reconstructive potential of each stem design depends on the patient's femoral morphotype. Across all CPAH types, the short stem was the best-fit implant, whereas a mismatch between anatomy and stem design was evident in up to 80% of the cases using the anatomic stem design. CONCLUSIONS: The CPAH classification provides a comprehensive classification system for femoral morphotypes. It enables a phenotyping approach in THA planning and provides practical guidance for individualized implant selection.