Bone imaging after total replacement arthroplasty of the hip joint. A follow-up with different radiopharmaceuticals.

Bone imaging was done in patients after total replacement arthroplasty of the hip joint every 3rd month using 99mTc-HEDP and 18F. Uptake ratios were estimated over cup/normal hip and femur prosthesis/normal thigh. Ratios decline rapidly and reach a stable level 6-9 months, postoperatively. Eight cases of late infection were predicted correctly 1-3 months before any radiologic evidence was present. In four cases there had been false-positive results with 99mTc-HEDP while 18F gave always correct information except in cases of soft tissue inflammation. Here both 99mTc-HEDP and 18F ratios were elevated. The early diagnosis of late complications after replacement arthroplasty seems to be possible. The clinical significance, however, is low: only one out of eight patients with manifest infection is still on conservative treatment. Bone imaging should be done to exclude late infection as a cause of pain after total replacement arthroplasty of the hip joint only.