Accuracy and Precision of Femoral and Tibial Bone Resections Using Manual Unrestricted Kinematic Alignment in Total Knee Arthroplasty: A Retrospective Digital Caliper Study

Purpose: To evaluate the accuracy and precision of both femoral and tibial bone resections in unrestricted kinematic alignment total knee arthroplasty (uKA TKA) performed with manual instrumentation, using postoperative digital caliper measurements. Methods: A retrospective study analyzing prospectively collected data on femoral and tibial resection thickness in 73 patients undergoing primary uKA TKA. Femoral cuts were performed with manual KA-optimized instrumentation in all cases. Tibial cuts were performed manually in 58 cases and with patient-specific instrumentation (PSI) in 15; PSI tibial resections were excluded from tibial analyses. Postoperatively, resection thickness was measured using a digital vernier caliper (0.2 mm resolution) at predefined sites: distal medial femur (DMF), distal lateral femur (DLF), posterior medial femur (PMF), posterior lateral femur (PLF), medial tibial plateau (MTP), and lateral tibial plateau (LTP). Resection error was defined as measured minus target thickness (mm). Accuracy was reported as mean signed error; precision as SD of signed error; absolute errors and error class distributions were also reported. Postoperative measurements reflect the accuracy and precision of the initial manual tibial resections, excluding any subsequent corrective cuts. Results: A total of 408 measurements were analyzed (292 femoral, 116 tibial). Mean signed error across resections was low and consistently negative (−0.15 to −0.31 mm), with infra-millimetric precision (SD 0.45 to 0.73 mm). Mean absolute errors remained low across sites (0.35 to 0.62 mm). The proportion of errors outside ±0.5 mm ranged from 21.1% (PLF) to 44.4% (LTP) and those outside ±1.0 mm from 1.4% (DMF) to 18.5% (LTP). No errors exceeded ±2.0 mm. Conclusions: Manual caliper-verified unrestricted KA TKA achieved high accuracy and precision for both femoral and tibial resections. However, these findings do not establish superiority over other techniques and do not account for final implant position, soft-tissue balance, or clinical outcomes. This study provides quantitative data on tibial resection accuracy in uKA TKA and may serve as a benchmark for evaluating the performance of technology-assisted techniques.