Bone scanning in the assessment of patellar viability following knee replacement.

In an attempt to diagnose avascular necrosis (AVN) of the patella, a potential complication of the surgical procedure, 99mTc-MDP bone scanning was performed pre- and postoperation in 37 patients treated by 41 total knee arthroplasties. The normal immediate postoperative scan should demonstrate increased radionuclide uptake in the patella when compared to preoperative scans. Decreased uptake was seen in four cases in the early postoperative period. This latter group was believed to be at risk for osteonecrosis and stress fracture of the patella. For this reason, prophylactic restriction of activity was instituted, with subsequent return of normal radionuclide uptake in the patella. Bone scanning provides an effective method of early diagnosis of patients at risk for the development of AVN and secondary patellar fractures following total knee arthroplasty.