Muscular Recovery of Hip Flexors and Extensors after Two-incision Total Hip Arthroplasty

Background: The influence of two-incision total hip arthroplasty on muscular function hasnot been reported. We hypothesized that recovery could be different for thehip flexors and extensors because an intermuscular interval was used in theflexors but a trans-muscular approach was used for the extensors.Methods: Two-incision total hip arthroplasties were performed in 10 patients (8 menand 2 women) with a mean age of 47.2 years (range, 27 to 63 years). Muscletorques were measured prospectively in the 10 patients using a cybexdynamometer preoperatively, 6 weeks postoperatively, and at the latest follow-up.Results: It was found that muscle torque improved from 0.51 (preoperative) to 0.68Ft-Lbs/Lbs 6 weeks postoperatively. (p = 0.007) However, this improvementwas contributed by the flexors but not the extensors. In contrast to the flexors,the torques of the extensors significantly decreased to 86%, 78%, and63% at the angular velocity of 60°/min, 90°/min, and 180°/min, respectively,6 weeks postoperatively. At the most recent follow-up (average 40 ± 2months), differences could not be found in either the flexors or the extensorscompared with the unaffected side.Conclusion: The causes for the delayed recovery of hip extensor muscles could be relatedto surgical techniques that traverse the muscle during femoral canal preparationand stem implantation. This study suggests that the two-incision techniquecan be further refined in view of the muscular function.