Early pain relief and function after posterior minimally invasive and conventional total hip arthroplasty. A prospective, randomized, blinded study.

BACKGROUND: Few prospective randomized studies have demonstrated benefits of minimally invasive total hip arthroplasty when compared with conventional total hip arthroplasty. We hypothesized that patients treated with a posterior mini-incision would have better results than those treated with a posterior long incision with regard to the achievement of established goals for pain relief and functional recovery permitting hospital discharge by the second postoperative day.

METHODS: Sixty of 231 eligible patients were randomized (with thirty in each group) to have a total hip arthroplasty performed through either a posterior mini-incision (10 +/- 2 cm) or a traditional long incision (20 +/- 2 cm). After completion of the total hip arthroplasty, the mini-incision group underwent extension of the skin incision to 20 cm. Patients were evaluated on the basis of self-determined pain scores, requirements for pain medicine, need for assistive gait devices, and time until discharge. Gait analysis provided objective functional assessment.

RESULTS: The average hospital stay was 63.2 +/- 13.3 hours in the mini-incision group and 73.6 +/- 23.5 hours in the long-incision group (p = 0.04). More patients with a mini-incision were discharged by the second postoperative day (p = 0.003) and more were using just a single assistive device at the time of discharge (p = 0.005). As scored on a verbal analog scale of 0 to 10 points, patients with a mini-incision had less pain on each postoperative day and the pain score remained significantly lower at the time of discharge (mean, 2.2 +/- 1.0 points compared with 3.1 +/- 0.9 points in the long-incision group; p = 0.002). After hospital discharge, there were no clinical differences in pain or function between the two groups of patients.

CONCLUSIONS: Compared with conventional total hip arthroplasty performed through a posterior incision, posterior minimally invasive total hip arthroplasty resulted in better early pain control, earlier discharge to home, and less use of assistive devices. Subsequent evaluations at six weeks and three months showed equivalency between the clinical results in the two groups.

LEVEL OF EVIDENCE: Therapeutic Level I.