Background
The use of the direct lateral approach and its modifications for total hip arthroplasty (THA) may lead to postoperative abductor weakness. Assessment of abductor muscle function by the use of quantitative electromyography (EMG) aims to investigate the nature of abductor muscle dysfunction.
Methods
We conducted a study on 40 patients who had hip replacement through the modified direct lateral approach. EMG was performed before surgery on the affected and normal sides and repeated on the operated side after surgery by 6 and 12 weeks. Analysis of EMG of the three abductor muscles was done in all patients.
Results
EMG evidence of acute denervation of hip abductors was present in 15 hips (37.5%) after 6 weeks. Improvement of EMG findings occurred in 8 out of 15 patients. Quantitative electromyography (QEMG) showed early significant increase in amplitude in all muscles and decrease in duration in gluteus medius (G. Med) with a pattern of acute nerve injury. At 12 weeks, the values of duration, amplitude, and phase were insignificantly different from the preoperative values signifying the return of near normal muscle activity.
Conclusion
The use of modified direct lateral approach can cause denervation of hip abductors. It is common in the early postoperative weeks. However, it tends to improve and the residual weakness in some patients is not marked. Quantitative electromyography showed that partial denervation is related to superior gluteal nerve stretching and not to direct injury of the terminal branches of the nerve through the incision.