Assessment of patient-specific instrumentation precision through bone resection measurements

Purpose: In the present study, the precision of two patient-specific instrumentation (PSI) systems for total knee arthroplasty (TKA) was evaluated by comparing bony resection thicknesses of the pre-operative PSI planning and intra-operative measurements by a vernier calliper. It was hypothesized that the data provided by pre-operative planning were accurate within ±2 mm of the bone resection thickness measured intra-operatively. Methods: Forty-one patient-specific TKAs were examined: 25 performed with Visionaire® technology and 16 with OtisMed® system. PSI accuracy was analysed comparing the resected bone thicknesses in the femoral and tibial cuts with pre-operatively planned resections. To determine pre-operative planning precision, the thickness values reported by the PSI planning were subtracted from the values reported intra-operatively by the calliper. Results: The mean absolute differences between pre-operatively planned resections and corresponding intra-operative thickness measurements ranged from a minimum of 2.6 mm (SD 0.8) to a maximum of 3.6 mm (SD 1.3) in all three anatomical planes in both groups. In every plane, the mean absolute discrepancies between planned resections and measured cuts differed significantly from zero (p < 0.0001). The proportion of differences within ±2 mm between intra-operative measured resections and planned PSI cuts occurred in more than 90 % of the cohort for femoral distal resections. Less precision was reported for the femoral posterior medial cuts (70.7 % within ±2 mm) and the tibial cuts (70.7 % on the medial, 75.6 % on the lateral side). Prosthetic component alignment on the coronal and transverse planes resulted in considerable deviations from the pre-operative planning. Conclusion: The two examined PSI technologies were accurate in femoral distal cuts, determining acceptable femoral component placement on the coronal plane. Posterior femoral and tibial cuts were less precise. Deviations from the pre-operative resection planning were reported in every plane. Inaccuracy was explained by ambiguous custom-made jigs placement on the bony surface. Level of evidence: III