Background: To assess the isokinetic muscle strength (IMS) of hip flexor and extensor muscles in patients treated with one-stage combined procedure for developmental dysplasia of the hip and analyze the effect of the status of hip muscles on IMS.
Methods: Twenty-two patients were included in the study. The mean age was 154.4+/-34.6 (110-216) months and the mean follow-up was 112.6+/-32.0 (68-159) months. All patients underwent complete tenotomy of the iliopsoas muscle to ease open reduction and had excellent results according to the modified McKay criteria of Barrett and type I hips according to the radiologic criteria of Severin. All patients had earlier magnetic resonance imaging examination that revealed reattachment of the iliopsoas in 7 (32%) patients. IMS measurements were performed at 120 degrees/s and 240 degrees/s. The peak torque (PT), PT angle, total work (TW), and average power (AP) values of operated and nonoperated hips were recorded separately for flexors and extensors.
Results: For flexors, TW and AP values were lower at the operated hip when compared with the nonoperated hip at both angular velocities. PT was only lower at the operated hip at 120 degrees/s. For extensor muscles, PT, TW, AP, and PT angle showed no statistically significant difference at either angular velocity. For flexors, the PT deficit between the operated and nonoperated hips at 120 degrees/s and 240 degrees/s was measured as 15.3% and 8.0%, respectively. There was no difference between the flexor muscles of operated and nonoperated hips considering PT, TW, and AP at both angular velocities in patients with reattachment. The IMS deficit of flexor muscles at 120 degrees/s was significantly higher in patients without reattachment of iliopsoas when compared with those with reattachment, and correlated to the widths of the iliopsoas muscle at levels II and III.
Conclusions: Assessing the results of surgical treatment of DDH with conventional radiologic and functional criteria might be misleading in some patients with excellent results because some of these patients, particularly those without reattachment of the iliopsoas muscle, experience significant weakness in hip flexion.