Learning curve for a modified Watson-Jones minimally invasive approach in primary total hip replacement: analysis of complications and early results versus the standard-incision posterior approach.

We analysed the learning curve of an anterolateral minimally invasive (ALMI) approach for primary total hip replacement (THR). The first 42 THR's with large-diameter heads implanted through this approach (group 1) were compared to a cohort of 58 THR's with a 28-mm head performed through a standard-incision posterior approach (group 2). No selection was made and the groups were comparable. Implant positioning as well as early clinical results were satisfactory and were comparable in the two groups. In group 1, the rate of intraoperative complications was significantly higher (greater trochanter fracture in 4 cases, cortical perforation in 3 cases, calcar fracture in one case, nerve palsy in one case, secondary tilting of the metal back in 2 cases) than in group 2 (one nerve palsy and one calcar crack). At 6 months, one revision of the acetabular cup was performed in group 1 for persistent pain, whereas in group 2, we noted 3 dislocations (2 were revised) and 2 periprosthetic femoral fractures. Our study showed a high rate of intra- and perioperative complications during the learning curve for an ALMI approach. These are more likely to occur in obese or osteoporotic patients, and in those with bulky muscles or very stiff hips. Postoperative complications were rare. The early clinical results are excellent and we may expect to achieve better results with a more standardised procedure. During the initial period of the learning curve, it would be preferable to select patients with an appropriate morphology.