Changes in Alignment of Ipsilateral Knee on Computed Tomography after Total Hip Arthroplasty for Developmental Dysplasia of the Hip

OBJECTIVE: To assess the changes in alignment of ipsilateral knee joint after total hip arthroplasty (THA) for patients with developmental dysplasia of the hip (DDH). METHODS: Thirty‐four patients with DDH (38 hips) who underwent THA between February and December 2008 were included in the study: 4 men and 30 women with a mean age of 56.2 years. According to Crowe classification, 11 patients were grade I, 12 were grade II, 9 were grade III, and 6 were grade IV. Computed tomography scans were performed from the anterior superior iliac spine to the tibial tubercle before surgery and at last follow‐up. Femoral anteversion angle, leg lengthening, and knee alignment, including patellar tilt angle, lateral patellar displacement, and tibiofemoral rotation angle, were measured on computed tomography scans, and their relationships were analyzed. RESULTS: The mean follow‐up period was 51.5 months (range, 39–70 months). There were no intraoperative fractures, and no infections occurred during the follow‐up period. One patient developed deep venous thrombosis and another suffered from femoral nerve palsy. The mean preoperative Harris Hip Score was 48.9 ± 7.5 and improved to 91.2 ± 8.3 by the last follow‐up (P < 0.001). There was no sign of prosthetic loosening in all hips. Postoperatively, mean leg lengthening was 26.08 ± 21.81 mm (P < 0.001), femoral anteversion decreased 9.03° ± 12.80° (P < 0.001), and patellar tilt, lateral patellar displacement, and tibiofemoral rotation increased by 3.58° ± 4.96° (P < 0.001), 1.78 ± 3.36 mm (P = 0.002), and 2.56° ± 3.37° (P < 0.001), respectively. Postoperative increase in patellar tilt and lateral patellar displacement had significant linear relationships with the decrease in femoral anteversion (r = 0.621, P < 0.001 and r = 0.437, P = 0.0037, respectively). These results revealed that patellofemoral alignment would change more with the decrease in femoral anteversion. Postoperative increase in external rotation of the tibia had significant positive linear relationships with leg lengthening (r = 0.34, P = 0.037) and the decrease in femoral anteversion (r = 0.693, P < 0.001). These results revealed that the external rotation of the proximal tibia would increase with the leg lengthening or the decrease of femoral anteversion. Postoperative changes in patellar tilt and lateral patellar displacement had no significant linear relationships with leg lengthening (P = 0.795 and P = 0.082, respectively). CONCLUSIONS: Total hip arthroplasty for DDH could induce changes in alignment of ipsilateral patellofemoral and tibiofemoral joints, with increases in patellar tilt and displacement, and increases in external rotation of the tibia. These secondary alterations still existed at medium‐term follow‐up after surgery, which should be considered during THA for patients with DDH. Extended follow‐up is necessary to evaluate long‐term changes in the knee joint.