An evaluation of bone loss after total hip arthroplasty for femoral head necrosis after femoral neck fracture: a quantitative CT study in 16 patients.

This study was conducted to determine if bone and muscle loss is reversible in patients who had undergone total hip arthroplasty (THA) owing to necrosis of the femoral head after osteosynthesis for a displaced femoral neck fracture. The cortical bone mineral density (BMD), bone volume, bone mass, and muscle volume of the thigh and the BMD of the distal femur and proximal tibia were measured by quantitative computed tomography in 16 patients. Both extremities were measured just before reoperation. The measurements were repeated 3 and 6 months later. At reoperation, there was a mean 12% relative loss of bone mass and 23% loss of muscle volume in the middle femur on the fractured side compared with the uninjured side. In the distal femur and proximal tibia, there was a relative loss of BMD of 14% and 21% on the fractured side. Six months after reoperation, we found no change in bone mineral at any location on either side. The muscle of the thigh showed a gain in volume of 20% on the reoperated side but no change on the uninjured side. At the time of reoperation, we noted a marked bone and muscle loss on the fractured side. We failed to note any restoration of bone mineral after THA despite remobilization, which is expressed as an increase in muscle volume on the reoperated side. This study indicates that osteopenic bone has difficulties in adapting to patients' improved mobility after reoperation.