Shank angular deceleration as a weight-acceptance marker in healthy and hip osteoarthritis walking.

BACKGROUND: Weight acceptance during walking is essential for shock absorption, limb stability, and step-to-step transition, but its characterization with shank-mounted wearable sensors remains incomplete. Established early-stance events such as foot-flat, braking force peak, and opposite toe-off do not fully describe shank progression during loading response. RESEARCH QUESTION: Can the shank angular deceleration peak (SAD) serve as an inertial measurement unit (IMU)-compatible marker of early-stance shank progression, and does it provide distinct, complementary information alongside foot-flat, braking force, and opposite toe-off? METHODS: Two datasets were analyzed. In a healthy young dataset of 15 adults and 12594 steps, IMU, optical motion capture, and force-plate recordings were used to compare SAD timing between methods and across walking speeds, footwear, and heel-lift conditions. A separate total hip arthroplasty dataset of 80 healthy controls and 106 patients was used for asymmetry and discrimination analyses. RESULTS: SAD timing showed excellent agreement between IMUs and optical motion capture in the healthy young dataset, with ICC(2,1) values of 0.95 in barefoot and 0.92 in shod walking. Event timings changed systematically with speed, footwear, and heel-lift conditions, and SAD occurred after foot-flat during early stance. In the total hip arthroplasty dataset, asymmetry of all markers was higher before surgery and lower after surgery. Opposite toe-off and braking force peak showed the strongest discrimination between healthy controls and preoperative patients (AUC 0.81 and 0.80), whereas SAD showed moderate discrimination (AUC 0.72). SIGNIFICANCE: SAD complements established early-stance events and is promising for wearable assessment of shank progression during weight acceptance.