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.

Does component placement affect short-term clinical outcome in robotic-arm assisted unicompartmental knee arthroplasty?

AIMS: The purpose of this multicentre observational study was to investigate the association between intraoperative component positioning and soft-tissue balancing on short-term clinical outcomes in patients undergoing robotic-arm assisted unicompartmental knee arthroplasty (UKA). PATIENTS AND METHODS: Between 2013 and 2016, 363 patients (395 knees) underwent robotic-arm assisted UKAs at two centres. Pre- and postoperatively, patients were administered Knee Injury and Osteoarthritis Score (KOOS) and Forgotten Joint Score-12 (FJS-12). Results were stratified as "good" and "bad" if KOOS/FJS-12 were more than or equal to 80. Intraoperative, post-implantation robotic data relative to CT-based components placement were collected and classified. Postoperative complications were recorded. RESULTS: Following exclusions and losses to follow-up, 334 medial robotic-arm assisted UKAs were assessed at a mean follow-up of 30.0 months (8.0 to 54.9). None of the measured parameters were associated with overall KOOS outcome. Correlations were described between specific KOOS subscales and intraoperative, post-implantation robotic data, and between FJS-12 and femoral component sagittal alignment. Three UKAs were revised, resulting in 99.0% survival at two years (95% confidence interval (CI) 97.9 to 100.0). CONCLUSION: Although little correlation was found between intraoperative robotic data and overall clinical outcome, surgeons should consider information regarding 3D component placement and soft-tissue balancing to improve patient satisfaction. Reproducible and precise placement of components has been confirmed as essential for satisfactory clinical outcome. Cite this article: Bone Joint J 2019;101-B:435-442.