AI assisted video analysis of the Trendelenburg Test: A Feasibility Study

Background: The Trendelenburg test is widely used to assess hip abductor function but is traditionally graded as a binary sign, limiting sensitivity and reliability. Compensatory trunk lean may mask pelvic drop and further reduces diagnostic accuracy. Advances in artificial intelligence (AI) and markerless motion capture provide an opportunity to quantify pelvic obliquity, trunk lean, and knee alignment objectively using simple video-based systems. Methods: A cross-sectional feasibility study was conducted in an elective hip clinic. Twelve adult patients (seven post-total hip arthroplasty, five with osteoarthritis, performed bilateral single-leg stance while recorded by a single posterior camera (4K, 60 fps). Videos were analysed using an AI-based application (OnForm) to extract pelvic obliquity, trunk lean, and knee alignment change. Feasibility metrics included analysis success rate, retakes required, and workflow timing. Outcomes were reported as medians with interquartile ranges (IQR) and ranges. Results: All patients completed the protocol with analysable recordings (100% technical success). The mean total workflow time was 217 seconds (IQR 206.8–230.3; range 193–244). Median worst pelvic obliquity was 0.0° (IQR –1.0° to +1.5°; range –5° to +6°). Median trunk lean was 4.5° (IQR 2.8°–9.0°; range 2°–10°). Median knee alignment change was 3.0° (IQR 2.0°–4.0°; range 1°–8°). Trunk lean ≥5° was seen in 6 patients (5/7 post-THA), while significant pelvic drop (≤ –4°) occurred in only one patient. Knee deviations ≥3° were observed in 8 patients (67%). Conclusions: AI-assisted single-camera analysis of the Trendelenburg test is feasible, rapid, and clinically informative. The method consistently quantified pelvic, trunk, and knee angles, revealing that post-THA patients frequently compensate with trunk lean rather than pelvic drop. These findings support the integration of objective video-based Trendelenburg assessment into outpatient orthopaedic practice.