Conventional hip arthroplasty femoral stems bypass the femoral neck for fixation. The femoral neck and proximal femur has a complex anatomy and interosseous structure to facilitate transfer of mechanical load in axial, compression bending and torsion mechanisms. von Mises analysis suggests a short stem, fixed in the femoral neck would maintain proximal femoral biomechanics, achieve physiological load transfer to the femoral neck and preserve bone stock and function. The strong calcar bone provides excellent opportunities for implant fixation and load transfer. The Muscle Sparing Arthroplasty (MSA™) is a short femoral stem designed to achieve implant fixation in the femoral neck. The specific design features including a trapezoidal cross section; proximal conical flare; porous coating and lateral T back enhance proximal fixation and compressive load transfer to the calcar and femoral neck. We report 54 hip arthroplasties in 49 patients with an average follow up of 18 months. All hip arthroplasties showed evidence of new bone formation in the proximal femoral neck and calcar region. This consisted of new bone streaming from the original calcar bone, in a strut fashion up to the conical flare of the implant. In 18 patients additional new bone formation occurred proximal to the neck osteotomy. This pattern of bone formation is consistent with predictions.Method
Results
In order to improve the fixation of the stem in primary Charnley low-friction arthroplasty, the medullary canal was routinely closed off with a cancellous bone block. A prospective study of 611 consecutive arthroplasties were carried out between 1 and 5 1/2 years (average 2 years and 9 months) after operation. There were two cases of radiological loosening of the stem, both of which could have been avoided. Five other patients showed demarcation of the bone-cement junction at the calcar; two of these are considered to be "at risk" of loosening. There was no evidence of radiological loosening of the stem in 604 cases and the method is recommended for routine use in primary total hip arthroplasty.
Nine patients have been reviewed at an average period of 22 years after a Watson-Jones tenodesis performed for chronic instability of the ankle. Only three patients had complete relief of symptoms. Two favourable early results deteriorated 7 and 10 years after operation. Radiographic examination revealed full correction of both anterior and lateral instability of the talus in only two cases. Talar tilt was controlled more successfully than increased anterior drawer movement. Long-standing instability was associated with the formation of marginal exostoses, the severity of which appeared proportional to the degree of instability.
