[Prospective and comparative study of minimally invasive posterior approach versus standard posterior approach in total hip replacement].

PURPOSE OF THE STUDY: There have been few prospective studies comparing minimally invasive approaches for total hip replacement. We wanted to ascertain the contribution of the minimally invasive posterior approach in comparison with the standard posterolateral approach in terms of early outcome.

MATERIALS AND METHODS: This was prospective comparative consecutive series of patients. Patients with major architectural problems or undergoing revision arthroplasty were excluded. One hundred ten patients (116 hips) were divided into two groups which were comparable for number of patients, gender, age, body mass index, indication for surgery, and preoperative function scores. The preoperative ASA score was lower in the minimally invasive group (p=0.04). The patients were in the lateral reclining position for the two approaches and classical instrumentation using the same implants (stems and cemented or non-cemented cups) were used. We noted operative time and blood loss (using the Brecher method based on the hematocrit at day 1 and 5 and the number of blood transfusions), postoperative pain, and implant position. Functional outcome was assessed with the modified Harris score and the WOMAC index (at 6 weeks and 3 and 6 months). Statview(R) was used to search for statistical significance considering p<0.05 as significant.

RESULTS: Mean length of incision was 8.5 cm versus 15.1 cm. Mean blood loss was significantly less in the minimally invasive group (p=0.027) as was the level of postoperative pain as confirmed by the lesser consumption of morphine analgesics (p=0.006). Other operative variables as well as implant position were comparable. There were no major complications in the minimally invasive group. In the standard group, there was one case of common peroneal nerve palsy, two dislocations, and two fractures related to falls after prosthesis implantation. The WOMAC index was better after the minimally invasive approach at six weeks and at three months (p<0.05). The modified Harris score was better only at six weeks. Functional outcome and pain became comparable thereafter.

DISCUSSION AND CONCLUSION: The minimally invasive posterior approach does not require an orthopedic table nor specific instrumentation. A minute procedure is required with ligature of the posteromedial circumflex artery of the thigh to improve exposure and limit intraoperative bleeding. It enables satisfactory reproducible implant positioning. Conversion to an open posterolateral approach is possible if needed. The minimally invasive posterior approach enables a reduction in intraoperative bleeding and in postoperative pain while allowing earlier more rapid rehabilitation. Early clinical outcome is better but beyond six weeks, the functional results are comparable for the two approaches. The minimally invasive posterior approach is a reliable reproducible approach with a progressive learning curve.