Introduction: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. The surgical approach may affect the blood supply to the femoral head. We compared the changes in femoral head oxygenation resulting from the extended posterior approach to those resulting from the anterolateral approach, the trochanteric flip approach and a modified, soft tissue preserving posterior approach.

Methods: We recruited 48 patients who underwent hip resurfacing arthroplasty (HRA) to measure bone oxygen levels. A calibrated gas-sensitive electrode was inserted in the femoral head following division of the fascia lata. Intra-operative X-ray confirmed correct electrode placement. Base-line oxygen concentration levels were recorded immediately after electrode insertion and continuous measurements were then performed throughout surgery. All results were expressed relative to the baseline, which was considered as 100% relative oxygen concentration and changes during surgery through the posterior approach (n=10), the antero-lateral approach (n=12), the trochanteric flip approach (n=15) and the modified posterior approach (n=11) were compared.

Results: The relative oxygen concentration at the end of the procedure was significantly reduced when hip resurfacing was performed through the posterior (22%, SD 31%, p< 0.005) or a modified posterior (35%, SD 31%, p< 0.005) approach, but recovered in the anterolateral (123%, SD 99%, p=0.6) and trochanteric flip group (89%, SD 62%, p=0.5). Sub-group analysis of these two relatively blood preserving approaches showed that intra-operative oxygen concentration was significantly more consistent during surgery through the trochanteric flip approach (p< 0.02).

Discusssion and conclusion: This study has demonstrated that disruption of blood flow to the femoral head during HRA is dependent on the surgical approach. We therefore believe that blood supply preserving approaches (i.e. anterolateral, trochanteric flip) may be associated with a lower risk of avascular necrosis and femoral neck fracture.