UNILATERAL HIP-REPLACEMENT CAUSES BILATERAL CHANGES IN TIBIAL BONE-MINERAL CONTENT IN A CANINE MODEL

The presence of asymmetry in tibial bone mineral content (BMC) of the operated and control limbs at the end of the experimental period follo wing unilateral hip replacement surgery is used as a marker of limb fu nction. The goal of the present study was to determine the contributio n of ipsilateral and contralateral bone gain and lass to control-treat ed side differences in BMC of the tibia in dogs following unilateral h ip replacement surgery, Seven animals were followed longitudinally wit h single beam photon absorptiometry for 6 months after unilateral hip hemiarthroplasty. Bone loss, compared with preoperative baseline value s, was observed in both limbs, with recovery in bone mass beginning 1 month after surgery in the contralateral tibia and 3 months after surg ery in the ipsilateral tibia. Thus, the asymmetry in tibial BMC freque ntly seen after unilateral experimental hip replacement in the canine appears to be caused by differential timing of recovery of bone mass f ollowing a transient loss in both limbs, The mechanism defined in this study is in contrast to an alternative mechanism involving bone loss in the treated limb coupled with bone gain in the control limb.