Preoperative corrections are required for planning of patient-specific instrumentation in total knee arthroplasty.

Background: Patient-specific instrumentation (PSI) is attracting attention as a mechanical method of ensuring the accuracy of osteotomy during total knee arthroplasty (TKA). Few studies have focused on preoperative plans; thus, it is unclear how often initial plans have to be corrected preoperatively and intraoperatively. We investigated the frequency of corrections, the accuracy of intraoperative osteotomy, and postoperative alignment.

Methods: We analyzed 45 knees of 40 patients who underwent TKA using magnetic resonance imaging (MRI)-based PSI. We evaluated the frequency of corrections to preoperative plans and intraoperative corrections for each part. We also evaluated osteotomy error, defined as the difference between the planned and actual thickness of resected bone. Hip-knee-ankle angle (HKA), femoral component angle (FCA), and tibial component angle (TCA) on plain X-rays were evaluated for postoperative alignment.

Results: Corrections were made to the initial plans in 91.1% of cases with a mean of 3.3 corrections per knee. Intraoperative corrections were made in 57.8% of cases, with a mean of 0.6 corrections per knee. Mean absolute osteotomy error was around one millimeter, and values were within two millimeters over 80% of cases on most parts except the proximal lateral tibia. In terms of postoperative alignment, HKA was 178.5±1.7°, FCA was 89.0±1.6°, and TCA was 89.4±1.9°. Proportions of outliers were 11.1%, 15.6%, and 20.0%, respectively.

Conclusions: Most of the cases required preoperative corrections for planning of PSI. PSI may be useful for ensuring the accuracy of osteotomy and postoperative alignment.