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.