The aim of the study is to investigate the biomechanical effects on the pelvis of the anterolateral and posterolateral approaches at the time of hip arthroplasty. In particular the study investigates the change in stress distribution, and the change in muscle recruitment pattern following surgery.

The study uses an advanced finite element model of the pelvis, in which the role of muscles and ligaments in determining the stress distribution in the pelvis is included. The model is altered for the posterolateral approach by excision of the external rotators. Different levels of gluteal damage for the anterolateral approach are modelled by excising in turn the anterior third, half, and two-thirds of the gluteus medius and minimus. Although attempt is generally made to repair gluteal damage at the time of surgery, it is clear the muscle volume will be compromised immediately after surgery.

In support of previous clinical studies indicating an increased risk of limp, and pelvic tilt following the anterolateral approach, significant differences were found in the muscle recruitment pattern following the anterolateral, compared to the posterolateral approach. During single leg stance and walking force transfer to the iliacus and pectineus was observed. Required levels of muscle force, to maintain coronal balance, following the anterolateral approach were found to be close to maximum sustainable levels. In addition significant alteration to the pelvic stress distribution was found following the anterolateral approach. The effects of increasing gluteal damage for the anterolateral approach were progressive, and became more pronounced when more than fifty percent of the gluteus medius and minimus were damaged. Increases in stresses around the acetabulum were observed for the posterolateral, compared to the anterolateral approach.

Thus, based on a biomechanical evaluation, the anterolateral approach presents increased risk of limp, and pelvic tilt, in comparison to the posterolateral approach.