Abstract
Introduction
Hip resurfacing arthroplasty has been surgical options in younger and more active patients with osteoarthritis (OA) and osteonecrosis (ON) of the femoral head. Although excellent midterm results of this procedure have been reported, there is a concern about postoperative impingement between the preserved femoral neck and the acetabular component. There were few reports about kinematics after hip resurfacing. Therefore, the purpose of this study was to investigate the postoperative motion analysis after hip resurfacing using a noble dynamic flat-panel detector (FPD) system by which clear sequential images were obtained with low dose radiation exposure.
Materials and methods
11 patients (mean age: 47.8 ± 7.4), 15 hips were included in this study. There were ten men and one woman. The preoperative diagnoses were ON of the femoral head in 10 hips, OA in 3 hips, and others in 2 hips. Mean postoperative follow-up period was 25.1 ± 21.6 months. Femoral anteversion, cup inclination and cup anteversion were measured on computed tomography and plain radiograph. Impingement signs such as the reactive osteophyte formation and divot around the femoral neck were also investigated on the anteroposterior (AP) and lateral radiographs. Sequential images of active and passive flexion motion in 45-degrees semilateral position, and active abduction motion in a supine position were obtained using a noble dynamic FPD system.
Results
Mean femoral anteversion was 13.2° ± 9.1° and mean cup inclination and anteversion were 35.4° ± 2.3° and 6.8° ± 3.9°, respectively. The reactive osteophyte formation apeared in 1 hip (6.7%) on AP radiograph and 4 hips (26.7%) on lateral radiograph, and divot sign was observed in 1 hip (6.7%) on each radiographs. The location of the impingement signs were mostly observed at the anteroinferior portion of the femoral neck. In motion analysis, impingement between the femoral neck and the acetabular component was detected in 12 hips (80.0%) in flexion motion and 2 hips (13.3%) in abduction motion (Figure). There were no findings of the subluxation between the acetabular and femoral component after the impingement, but cooperative motion of lumber and pelvic flexion was occurred. None of the patients who had a impingement signs on plain radiographs and motion analysis had any symptoms and pain during hip motion.
Discussion and conclusion
Postoperative motion analysis is a noble and useful technique and that can detect various findings which could not be detected by the routine static radiographs. Also, postoperative kinematics after hip resurfacing remains unknown and we investigated it in detail using a noble dynamic FPD system. The present study indicated that impingement between the preserved femoral neck and the acetabular component and consequent cooperative motion of lumber and pelvic flexion were similar to the physiological motion of the nomal hip joint. No sign of the subluxation between the component proved the good stability of the resurfacing articulation. Proprioception of the preserved femoral neck can be related to this unique kinematics.
