The influence of two-incision total hip arthroplasty on muscular function has not been reported. We hypothesized that recovery could be different for the hip flexors and extensors because an intermuscular interval was used in the flexors but a trans-muscular approach was used for the extensors.
Two-incision total hip arthroplasties were performed in 10 patients (8 men and 2 women) with a mean age of 47.2 years (range, 27 to 63 years). Muscle torques were measured prospectively in the 10 patients using a cybex dynamometer preoperatively, 6 weeks postoperatively, and at the latest follow-up.
It was found that muscle torque improved from 0.51 (preoperative) to 0.68 Ft-Lbs/Lbs 6 weeks postoperatively. (p=0.007) However, this improvement was contributed by the flexors but not the extensors. In contrast to the flexors, the torques of the extensors significantly decreased to 86%, 78%, and 63% at the angular velocity of 60 degrees/min, 90 degrees/min, and 180 degrees/min, respectively, 6 weeks postoperatively. At the most recent follow-up (average 40 +/- 2 months), differences could not be found in either the flexors or the extensors compared with the unaffected side.
The causes for the delayed recovery of hip extensor muscles could be related to surgical techniques that traverse the muscle during femoral canal preparation and stem implantation. This study suggests that the two-incision technique can be further refined in view of the muscular function.