METAL-ON-METAL HIP RESURFACING AFFECTS FEMORAL HEAD OXYGENATION.

Abstract

Purpose This study aims to investigate blood flow in the femoral head during Metal-on-Metal Hip Resurfacing (MMHR) through the posterior approach by monitoring oxygen concentration during the operative procedure.

Methods Following division of fascia lata, a calibrated gas-measuring electrode was inserted into the femoral neck, aiming for the anterolateral quadrant of the head. Baseline oxygen concentration levels were detected after electrode insertion 2–3cm below the femoral head surface and all intra-operative measures were referenced against these. Oxygen levels were continuously monitored throughout the operation. Results of measurements from ten patients are presented.

Results Oxygen concentration was reduced during the surgical approach and average oxygen concentration following dislocation and circumferential capsulotomy dropped to 43% of baseline (Std.dev +/−37%), this was a highly significant reduction (p< 0.005). Insertion of implants resulted in a further significant drop in oxygen concentration (p< 0.02) to 16% of baseline (Std. dev +/−27%). Oxygen concentration rose slightly after relocation of the resurfaced joint and reconstruction of posterior soft tissues, reaching 22% (Std.dev +/−31%) of initial baseline oxygen levels. Considerable variation between subjects was observed. Three subjects had no remaining oxygen concentration at the end of surgery.

Conclusion Intra-operative measurement of oxygen concentration in blood perfusing the femoral head is feasible. During MMHR there is a dramatic decrease in femoral oxygenation during surgical approach and implant fixation. This may increase the risk of avascular necrosis and subsequent femoral neck fracture. Future experiments will determine if less invasive procedures or a different approach can protect the blood supply to femoral neck and head.