Accuracy of implant positioning in total ankle arthroplasty using patient-specific instrumentation: A weightbearing CT analysis of landmark-based parameters.

BACKGROUND: Patient-specific instrumentation (PSI) may improve implant positioning in total ankle arthroplasty (TAA), but three-dimensional validation with postoperative weightbearing CT (WBCT) remains limited. This study assessed the accuracy of the INBONE Prophecy system. METHODS: Fifty-four patients undergoing INBONE II TAA with available Prophecy planning and postoperative WBCT were retrospectively reviewed. Planned and postoperative implant positions were compared for medial tibial component-to-medial malleolus distance, talar stem-to-subtalar joint distance, and talar cut relative to the horizontal axis. Reliability was evaluated using intraclass correlation coefficients. RESULTS: Distance measurements showed high accuracy, with most cases within 1 mm. Poor accuracy (>2 mm) occurred in 20% of medial malleolar and 7.7% of subtalar measurements. ICCs ranged from 0.79 to 0.95. The mean absolute angular difference for talar cut was 2.91°. CONCLUSION: INBONE Prophecy PSI accurately reproduced planned distance-based positioning, while sagittal talar alignment was more variable.