Sit-to-Stand Adaptations in Pre-Operative Cam-Type Femoroacetabular Impingement: A Kinematic and Coordination Analysis

Background: Individuals with cam-type femoroacetabular impingement (FAI) demonstrate altered lower-limb biomechanics during functional activities, yet little is known about inter-joint coordination during sit-to-stand (STS). This study compared sagittal-plane kinematics, inter-joint coordination, and coordination variability during STS in individuals with and without cam-type FAI. Methods: Twenty-four adults with symptomatic cam-type FAI and 19 healthy controls completed five STS trials while three-dimensional motion capture and ground reaction force data were collected. Sagittal-plane hip, knee, ankle, pelvis, and spine kinematics were analyzed using statistical parametric mapping and discrete measures. Spine-hip and hip-knee coordination variability were quantified using modified vector coding. Group differences were evaluated using independent t-tests and mixed ANOVAs. Results: Participants with FAI demonstrated reduced early-phase hip range of motion and greater peak knee flexion during STS compared with controls. Statistical parametric mapping did not reveal statistical group differences in single joint kinematics during early and late phase STS. A significant group-by-phase interaction was observed for spine-hip coordination variability, with individuals with FAI exhibiting greater variability during early STS (p = 0.010, d = 0.92), but not during late STS. No between-group differences were identified for hip-knee coordination variability. Conclusions: Individuals with cam-type FAI demonstrate altered spine-hip movement organization during STS, characterized by greater early-phase coordination variability and reduced hip flexion range of motion. Clinical significance: These findings suggest that movement strategies in people with FAI during STS may be more strongly reflected in variability of inter-joint coordination patterns than single joint kinematics.