Description
Objectives: Even though unicompartmentalknee arthroplasty (UKA) could be used in nearly 50% of knee replacement cases, thistechnique is known to be less reproducible than total knee arthroplasty (TKA), and therefore underused. Restoring the joint line has proved essential to achieve long-termimplant survival and to improve UKA clinical outcomes. Preoperative valgus stress radiographs allow physicians to assess varusdeformity correction and predictpostoperative alignment. The objective ofthis study was to describe a planning methodfor medial UKA implantation usingpreoperative stress radiographs to measurethe thickness of tibial and femoral boneresections, and to validate this method withdata from an image-based robotic surgerysystem.
Methods: We proposed a new planningmethod for medial UKA based on valgusstress radiographs and validated it with animage-based robotic surgery system. Thisretrospective study involved radiographicmeasurements based on preoperative radiographs of 76 patients who underwentimage-based robotic medial UKA. Preoperative anteroposterior stress radiographs of the knee were used tosimulate UKA implantation. The UKA technique was based on Cartier's angle and aimed at restoring the joint line. The total dimension was 14mm (8mm for minimaltibial component and polyethylene insert + 4mm for femoral component + 2mm forsafety laxity). Bone resections weremeasured in the preoperative valgus stress radiographs and then against theintraoperative bone resection data providedby the robotic system. Inter- and intra-observer reliability was assessed using 25 measurements.
Results: The mean planned tibial resectionmeasured in the radiographs was 4.3 ± 0.4 [2.9-5.8], while the mean robotic resectionwas 4.2 ± 0.5 [2.7-5.8] (mean difference = 0.15 mm, 95% CI [-0.27 - 0.57]). There wasa strong correlation between these two values(Pearson's rank R = 0.79, P < 0.001). Intra- and inter-observer reliability were also strong(Pearson's rank R = 0.91, P < 0.001, and Pearson's rank R = 0.82, P < 0.001, respectively). The mean planned femoral bone resection measured in the radiographswas 2.7 mm ± 0.7 [1-4.5], while the meanrobotic resection was 2.5 ± 0.9 [1-5] (mean difference = 0.21 mm, 95% CI [-0.66 - 1.08]). There was a strong correlationbetween these two values (Pearson's rank R = 0.82, P < 0.001). Intra- and inter-observerreliability were also strong (Pearson's rank R = 0.88, P < 0.001, and Pearson's rank R = 0.84, P < 0.001, respectively).
Conclusions: This study describes and validates a simple and reproducible preoperative planning method to determine femoral and tibial bone resection for medial UKA implantation using antero-posterior valgus stress radiographs, leaving a medial safety laxity of 2mm. It represents a veryvaluable contribution to the understanding ofUKA principles, which can serve to extendits indications, and increase reproducibilityof the surgical technique.
