Value of quantitative serial three phase bone scan for diagnosis of total knee arthroplasty loosening in case of initial equivocal findings

 The study goal was to determine whether serial quantitative three phase [99mTc]Tc-MDP bone scintigraphy can provide additional information to accurately predict loosening in symptomatic patients after total knee arthroplasty (TKA) whose initial [99mTc]Tc-MDP study was not diagnostic.

 We retrospectively include bone scans of 125 patients suffering pain after knee arthroplasty. 52 patients with equivocal image findings on three phase planar bone scintigraphy and inconclusive clinical parameters were candidate for follow up examination. Quantification was performed on delayed planar views of both image series and the ratio of pathological peri-prosthetic tracer uptake to normal bone was evaluated. The change in periprosthetic abnormal to normal bone uptake ratios was analyzed within 6-months interval to assess. Interpretations were validated by clinical follow-ups or revision operation.

 Initial quantitative planar analysis in periprosthetic region did not relevantly enhance the diagnostic performance of bone scanning in assessing knee prosthetic loosening. Six months follow-up images improve the diagnostic power of bone scan but it was not statistically significant. However, a threshold of 3.9% rise in periprosthetic abnormal to normal bone uptake ratio of the "tibial plateau" within 6 months markedly improved the performance of three phase [99mTc]Tc-MDP  for the detection of loosening (sensitivity 87%, specificity 89%, p value = 0.002). 

 Equivocal scintigraphic findings are still a main challenge in management of TKA complications. Follow-up quantitative bone scan improves the diagnostic impact of bone scintigraphy for detection of loosening process in equivocal cases of TKA.