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 necros is of the femoral head after osteosynthesis for a displaced femoral neck fr acture. The cortical bone mineral density (BMD), bone volume, bone mass, an d muscle volume of the thigh and the BMD of the distal femur and proximal t ibia were measured by quantitative computed tomography in 16 patients. Both extremities were measured just before reoperation. The measurements were r epeated 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 p roximal tibia, there was a relative loss of BMD of 14% and 21% on the fract ured 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 v olume 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 fra ctured side. We failed to note any restoration of bone mineral after THA de spite remobilization, which is expressed as an increase in muscle volume on the reoperated side. This study indicates that osteopenic bone has difficu lties in adapting to patients' improved mobility after reoperation.