Intraoperative Effect of Metal-On-Metal Hip

Intraoperative Effect Of Metal-On-Metal Hip Resurfacing Arthroplasty On Femoral Head Perfusion

Steffen RT, Smith SR, Gill HS, Beard DJ, Urban JPG, Murray DW
Nuffield Orthopaedic Centre, University of Oxford

Introduction: The incidence of femoral neck fracture is 2% after resurfacing hip replacement. Avascular necrosis is thought to be a contributory factor. The study aim was to investigate oxygen concentration in the femoral head during Metal-on-Metal Hip Resurfacing (MMHR).

Methods: In ten patients, following division of the fascia lata, a calibrated gas-measuring electrode was inserted into the supra-lateral quadrant of the femoral head via the femoral neck. X-ray confirmed placement of the electrode 2-3cms below the femoral head surface. Baseline oxygen concentration levels were recorded immediately on electrode insertion and used as reference for all intra-operative measures. Oxygen levels were monitored continuously throughout the operation.

Results: Oxygen concentration was reduced during the surgical approach and average oxygen concentration following dislocation and circumferential capsulotomy dropped significantly (p<0.005) to 38% of baseline (SD=26%). Insertion of implants resulted in a further significant drop in oxygen concentration (p<0.04) to 21% of baseline (SD=28%). Oxygen concentration rose slightly, but not significantly after relocation of the resurfaced joint and reconstruction of posterior soft tissues, reaching 22% of initial baseline oxygen levels. Considerable variation between subjects was observed.

Discussion and Conclusion: Intra-operative measurement of oxygen concentration in blood perfusing the femoral head is possible. During MMHR there is a dramatic decrease in femoral head 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 a different surgical approach can protect the blood supply to femoral head and neck.

Summary: Measurements of femoral head oxygenation during Metal-on-Metal Hip Resurfacing demonstrated a significant concentration decrease during surgical approach and implant fixation.

Keywords: Femoral head oxygenation, Metal-on-metal hip resurfacing, Blood flow, Surgical approach