In vivo 3D hip kinematics during racket swinging after total hip arthroplasty : evaluation of dynamic range of motion and liner-to-neck contact.

AIMS: Interest in sports participation after total hip arthroplasty (THA) has grown, and some patients return to playing racket sports after THA. However, dynamic hip kinematics and the risk of liner-to-neck contact during racket swinging remain unclear. This study aimed to evaluate in vivo, 3D dynamic hip kinematics during racket swinging after THA, and to identify factors associated with reduced liner-to-neck clearance, which may indicate an increased risk of liner-to-neck contact.

METHODS: A total of 19 patients (24 hips) who were playing racket sports after primary THA were evaluated. Dynamic radiological images of forehand and backhand swings were acquired using a flat panel detector. Hip joint kinematics were analyzed using a model-image registration technique. Liner-to-neck contact and clearance were assessed using postoperative CT data and kinematic analysis. Multivariable regression analyses identified factors associated with reduced posterior clearance.

RESULTS: The mean total axial hip rotation during racket swinging was 32°, with the hip maintained in slight flexion and abduction throughout the motion. Liner-to-neck contact occurred in two of 24 hips (8%), all at the elevated rim during maximum external rotation (ER). No bone-to-bone contact was observed. Posterior clearance below 10°, indicating an increased risk of posterior contact, was observed in nine hips (20%) during both extension and external rotation. Multivariable regression analysis identified elevated liner use, greater acetabular component anteversion, and greater hip extension angle at maximum ER as significant factors associated with reduced posterior clearance.

CONCLUSION: In vivo racket swinging after THA was performed within a kinematically safe range of motion without excessive axial rotation. Although liner-to-neck contact was infrequent, elevated liners and excessive acetabular component anteversion were associated with reduced posterior clearance during maximum external rotation. While racket swinging appears generally permissible after THA, careful liner selection and implant orientation are important to minimize the risk of liner-to-neck contact.