Prospective Double-blind Randomized Clinical Trial Comparing Gait Analysis and Clinical Function After Metal on Metal Total Hip Arthroplasty With Large Diameter Femoral Head and Metal on Metal Total Hip Resurfacing.

In the early 1960's Sir John Charnley revolutionized total hip arthroplasty (THA) with the introduction of polyethylene as a bearing surface. This innovation allowed THA to become a very successful procedure to treat degeneration of the hip joint, with excellent long term clinical outcome and patient satisfaction.

However, this technique requires sacrifice of the whole femoral head and part of the neck. This bone will not be available for future revision surgery, which seems inevitable in the younger patient. THA does not always allow precise reconstitution of normal hip biomechanics. The femoral canal is also violated, fat and cement embolism can occur and thrombogenic material is released in the bloodstream. Postoperatively the femoral stem can cause thigh pain, proximal stress shielding, and periprosthetic fracture may occur . Finally the use of a 28 millimeter non anatomic femoral head during conventional THA increases the risk of hip impingement and dislocation while limiting hip range of motion.

There is renewed interest in the concept of hip resurfacing and the use of large diameter femoral heads in total hip arthroplasty, since both these options recreate more optimal hip biomechanics. Total hip resurfacing is less invasive than conventional THA using a femoral stem and allows restoration of normal hip anatomy. Additionally, compared to conventional THA, hip resurfacing has the following advantages: preservation of the femoral head and neck, better hip stability, improved hip biomechanics (leg length, offset) and possibly better proprioception. Since the femoral canal is not violated, there is less risk of residual thigh pain, and patients probably have the sensation of a more normal feeling joint.

As for conventional THA with large diameter femoral heads, the use of a near anatomic head size (compared to the small 28mm diameter head use with conventional THA) restores normal stability, helps reduce the incidence of impingement and increases range of motion to a greater extent than hip resurfacing, and might improve proprioception as well. The investigators believe these advantages will have a positive influence on clinical function and gait pattern compared to conventional THA.

Gait analysis has demonstrated that gait pattern is modified after THA and patients do not recover normal gait. Kinematics analysis further showed that abnormal gait pattern is not only observed in the operated hip but also in other articulations, including the contra lateral limb. Walking kinetics are affected to some extent, especially the force generated by the lower limb and synchronization of muscle activity. Finally a subjective feeling of an abnormal hip function may still persists after THA.