Diagnostic accuracy of 99mTc-HDP SPECT/CT and MRI for foot and ankle osteoarthritis (ProSPECT-trial): Study protocol.

Background: Accurate localisation of symptomatic osteoarthritic (OA) lesions in the midfoot, hindfoot and ankle remains challenging due to their complex anatomy. Conventional radiographs have limitations in complex areas or overlapping structures. SPECT/CT has shown promising results in detecting symptomatic OA lesions, yet its superiority over MRI, the current standard for soft tissue pathology, remains uncertain. We designed the ProSPECT-trial to systematically investigate the diagnostic accuracy of SPECT/CT compared to MRI in OA of the foot and ankle.

Methods: The ProSPECT-trial is a non-randomised single-center prospective cohort study. Eligible patients with suspected OA of the midfoot, hindfoot and ankle are recruited. Diagnostic performance of SPECT/CT and MRI is assessed based on sensitivity, specificity, positive and negative predictive values. Intra- and interobserver reliability of both imaging modalities are evaluated. Imaging protocols include SPECT/CT using technetium-99^m hydroxymethylene disphosphonate (99mTc-HDP) and MRI without contrast agents. Anatomical regions are scored for OA presence using standardised radiographic- and clinical criteria. Diagnoses are confirmed via ultrasound-guided injections containing steroid and anaesthetics. With a calculated sample size of 369 patients, the study aims to show significant sensitivity and specificity differences between SPECT/CT and MRI, assuming a 15 % clinically relevant difference.

Implications: The ProSPECT trial assesses the diagnostic accuracy of SPECT/CT and MRI in midfoot, hindfoot, and ankle OA. The findings aim to standardise clinical decision-making and guide future treatment protocols, ultimately optimising patient care and resource utilisation in managing midfoot, hindfoot, and ankle OA.