Evaluating the Precision of Preoperative Planning in Patient Specific Instrumentation: Can a Single MRI Yield Different Preoperative Plans?

If PSI preoperative planning were perfectly precise, a single MRI would give rise to one preoperative plan. Our purpose was to determine whether a single MRI inputted into two different PSI software yielded differences in preoperative alignment determination, component sizing, and bone resection within the preoperative plan. This prospective comparative study evaluated 40 preoperative plans generated by two PSI software given identical MRI. Femoral and tibial component sizes differed between software in 37.5% and 30.0% of cases, respectively. The maximum difference in bone resection between software ranged from 2.2 mm to 5.1 mm. Surgeons should be prepared to intraoperatively deviate from PSI selected size by 1 size. It may be necessary to fine tune soft tissue balancing when using a PSI system.