Three-dimensional kinematics and kinetics of getting into and out of a car in patients after total hip arthroplasty.

Background: In modern society, car usage is one of the most important activities of daily living. However, the three-dimensional (3D) mechanics of getting into and out of a car in total hip arthroplasty (THA) patients have not been studied.

Research Question: This study aimed to elucidate the hip kinematics and kinetics of unilateral THA patients while getting into and out of a car.

Methods: 3D motion and ground reaction force data were collected for 40 unilateral primary THA and 30 control participants using motion capture of getting into and out of a car. Normalized joint power was used to determine the individual joint contribution and was calculated by dividing the power of each joint by the total lower-extremity power. These kinematic and kinetic data were compared between unilateral THA and control participants.

Results: When getting into the car using the surgical side as the pivot limb, the peak flexion, abduction angle, and normalized power of the pivot hip were significantly lower, and the normalized power of the contralateral ankle was significantly higher. The peak flexion and abduction angle of the pivot hip were significantly lower, and normalized contralateral hip power was significantly higher when getting out of the car. In getting into and out of the car using the contralateral side as the pivot limb, there was no significant difference in the range of motion (RoM) and normalized joint power.

Significance: The restoration of RoM and muscle strength in the surgical hip joint and adopting the normal side as the pivot limb may allow for a more appropriate balance in motion of getting into and out of a car, which will lead to safe mobility, assist in social participation, and improved quality of life.

Level Of Evidence: Level III, therapeutic study.