DECREASE IN BONE-MINERAL DENSITY AND MUSCLE MASS AFTER FEMORAL-NECK FRACTURE - A QUANTITATIVE COMPUTED-TOMOGRAPHY STUDY IN 25 PATIENTS

We performed a prospective, longitudinal, quantitative computed tomogr aphy (QCT) study of bone mineral density (BMD), cortical bone volume, bone mass and muscle volume in 25 patients who were operated on with o steosynthesis because of a displaced femoral neck fracture. Both legs were scanned within 3 days after the fracture, and 3 and 6 months afte r the operation. The measurements were performed by a computer tomogra ph equipped for bone mineral densitometry. We found some side differen ces among the patients at the time of fracture, but none of the differ ences was statistically significant. After 6 months, we found reductio ns in BMD in the distal femur and proximal tibia on the fractured side of 11% and 19%, respectively, as well as a reduction in BMD of 7% in the proximal tibia on the uninjured side. We found no changes in corti cal bone mass, either on the fractured femur or on the uninjured femur . The muscles of the thigh showed a loss of 9% on the fractured side, but a gain of 12% on the uninjured side. The findings of a bone toss i n the distal femur and proximal tibia of the fractured leg and in the proxima[ tibia of the healthy leg, but no cortical bone loss in the mi ddle femur on any side 6 months after the fracture, indicate that the cancellous bone is more sensitive to osteopenia. Moreover, this bone l oss is interpreted as mainly a posttraumatic effect, since we also fou nd a decrease in bone mineral on the uninjured side, despite a gain in muscle volume on that side, an overuse which was not sufficient to co unteract the posttraumatic effect on the bone of the uninjured side.