The uptake by the canine tibia of the bone-scanning agent 99mTc-MDP before and after an osteotomy.

The residue and extraction of technetium-labelled methylene diphosphonate (99mTc-MDP), a substance used in bone scanning, was examined in the canine tibia and found to be low. Examination of washout curves suggested that there were four compartments in cortical bone, a vascular, a perivascular, a bone fluid and a bone compartment. After an osteotomy in the canine tibia the residue of 99mTc-MDP increased. This was believed to be due to an increase in the blood supply to the bone and to an associated increase in new bone available for exchange. Bone scanning in a fracture is therefore a reflection of the vascular status of the bone being examined and of the uptake by bone. This is dependent on there being an adequate blood supply to the bone and an increased number of mineral-binding sites.