99Tcm-diphosphonate scanning as an aid to diagnosis of infection in total hip joint replacements.

Local infection following total hip joint replacement is often difficult to diagnose. Bone scanning with 99Tcm-diphosphonate has been used in an attempt to detect such infection by assessing uptake of 99Tcm in the hip. Posterior view dot scans of patients with total hip joint replacements were analysed quantitatively to determine the ratios of dots in regions around the acetabular, trochanteric and femoral parts of the prosthesis compared with normal bone. The scans were also assessed visually. Patients with definite evidence of infection showed higher uptake than control patients. The clearest distinction in uptake between the two groups was in the femoral shaft region. The data from these two groups of patients were used to propose diagnostic criteria for detecting abnormalities on scans. These criteria were applied to scans of a third test group of patients who had painful hips, but no definite evidence of infection. The numerical method of analysis is less subjective and may therefore be preferable as a means of providing evidence for or against a diagnosis of infection in patients with painful hip replacements.