Abstract
Rapid changes of direction, sudden stops, and jumping are prominent in basketball, contributing to a high incidence of anterior cruciate ligament (ACL) injuries. The Landing Error Scoring System (LESS) is a validated screening tool used to assess ACL injury risk based on kinematic patterns during a drop vertical jump. However, traditional motion capture methods used to obtain the required kinematics are costly and laboratory-dependent, limiting their use for routine athlete monitoring. This study evaluated the agreement between OpenCap, a smartphone-based markerless motion capture platform, and a gold standard Vicon motion capture system, and examined the feasibility of longitudinally monitoring LESS scores in collegiate basketball athletes across a competitive season. For validation, 10 healthy participants (4 males, 6 females) performed drop vertical jumps recorded simultaneously with OpenCap and Vicon. For longitudinal monitoring, 21 NCAA Division I basketball athletes (12 males, 9 females) were assessed at preseason, start of competition, and midseason. OpenCap demonstrated excellent agreement with Vicon (ICC = 0.884). Bland-Altman analysis showed a mean difference of -0.57 (95% CI: -1.19 to 0.05), indicating no systematic bias between systems. LESS scores did not change significantly across the season (p = 0.26), and positional differences were not statistically significant (p = 0.10), although a moderate effect size was observed (eta p2 = 0.062). Poor knee-flexion displacement, one of the most predictive LESS items, was present in approximately one third of athletes. These findings support the validity of OpenCap for facility-based ACL injury risk screening and longitudinal monitoring of athlete movement patterns.