Zeinab Paymani - Department of Nuclear Medicine, Children&#۰۳۹;s Medical Center Hospital, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
Forough Kalantari - Department of Nuclear Medicine, Rasoul Akram Hospital, Iran University of Medical Sciences, Tehran, Iran
Marzieh Ebrahimi - Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
Dominic Mathis - Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland, Bruderholz, Switzerland
Reinhold Ortmaier - Department of Orthopaedic Surgery, Ordensklinikum Barmherzige Schwestern Linz, Teaching Hospital of the Paracelsus Medical University Salzburg, Linz, Austria
Michael Hirschman - Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland, Bruderholz, Switzerland
Mohsen Beheshti - Division of Molecular Imaging and Theranostics, Department of Nuclear Medicine, University Hospital Salzburg, Paracelsus Medical University, Salzburg, Austria

Introduction: The study goal was to determine whether serial quantitative three phase [۹۹mTc]Tc-MDP bone scintigraphy can provide additional information to accurately predict loosening in symptomatic patients after total knee arthroplasty (TKA) whose initial [۹۹mTc]Tc-MDP study was not diagnostic.Methods: We retrospectively include bone scans of ۱۲۵ patients suffering pain after knee arthroplasty. ۵۲ 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 ۶-months interval to assess. Interpretations were validated by clinical follow-ups or revision operation.Results: 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 ۳.۹% rise in periprosthetic abnormal to normal bone uptake ratio of the "tibial plateau" within ۶ months markedly improved the performance of three phase [۹۹mTc]Tc-MDP  for the detection of loosening (sensitivity ۸۷%, specificity ۸۹%, p value = ۰.۰۰۲). Conclusion: 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.

Total knee arthroplasty, Quantitative bone scan, [۹۹mTc]Tc-MDP, Loosening, Serial bone scintigraphy