A novel iliofemoral classification for assessing surgical difficulty in direct anterior approach total hip arthroplasty: a retrospective cohort study

BACKGROUND: Direct anterior approach total hip arthroplasty (DAA THA) has become increasingly popular due to its muscle-sparing nature, but it remains technically challenging due to patient-specific anatomical variability. A comprehensive classification system for assessing surgical difficulty in DAA THA is lacking. This study aimed to develop a simple radiograph-based hip anatomic classification to estimate the difficulty of DAA THA. METHODS: This retrospective cohort study analyzed primary, unilateral DAA THA performed by a single surgeon from January 2021 to December 2024. On preoperative radiographs, the horizontal offset distance (HOD) and the vertical offset distance (VOD) between the lateral-most iliac crest and the lateral-most greater trochanter were measured. Restricted cubic splines and receiver operating characteristic curves were used to determine HOD and VOD cutoffs for difficult DAA THA and defined four subtypes (Type A: low VOD/low HOD, Type B: low VOD/high HOD, Type C: high VOD/high HOD, Type D: high VOD/low HOD). Perioperative, radiographic, inflammatory, functional, and complication outcomes were compared using one-way analysis of variance, chi-square and other statistical methods. Subgroup analyses were performed to assess generalizability. RESULTS: HOD and VOD showed weak, nonlinear inverse associations with operative time. Four subtypes were defined using the optimal cutoffs (HOD = 6.25 mm; VOD = 126.95 mm). Type A had the longest operative time and a less favorable perioperative profile, whereas Type C had the shortest operative time, less total blood loss, more frequent cups within Lewinnek safe zones, and better early functional recovery. CONCLUSIONS: This novel iliofemoral classification stratifies DAA THA technical difficulty and early outcomes and may support preoperative risk stratification and surgical planning.