Does robotic arm-assisted total knee arthroplasty have a role to play in large deformities?

Background: Total knee arthroplasty (TKA) for patients with a large preoperative deformity (more than 10° varus or valgus) remains a challenge leading to a high rate of outliers, unsatisfactory functional results, or early prosthetic loosening. Robotic arm-assisted TKA (RATKA) has shown improvements in implant positioning accuracy. This study aimed to assess RATKA implant positioning accuracy and functional results at one year postoperative for patients with a large preoperative deformity. Methods: From November 2019 to July 2022, 500 RATKA were performed. About 74 patients with more than 10° of varus or valgus global deformity were included. Each patient received a semi-constrained implant. The difference between the valgus or varus value planned intra-operatively and the varus or valgus measured on one-year postoperative X-rays has been assessed. Functional outcomes (VAS, range of motion, KOOS) have also been evaluated. Results: For varus, the mean difference was 0.54 ± 1.21°, all patients (100%) had a difference of less than 3° at one-year post-operative. For valgus, the mean difference was 0.63 ± 1.29°, most patients (92%) had a difference of less than 3° at one year postoperative. Overall, 98.6% (n = 73) of cases had a difference of less than 3° at one-year postoperative. The mean VAS was 1.6 ± 1.4 [1;4]. Mean flexion was 132 ± 7.6° [100;145]. A total of 69 patients (93%) had a good or excellent KOOS score (KOOS total > 70) at one year post-operative. Conclusion: For large preoperative deformities, RATKA provides a high degree of accuracy in implant positioning, permitting it to fit the desired alignment without compromising knee stability, and giving the possibility of using semi-constrained implants. At one year postoperative, functional results are encouraging and most patients have recovered an optimal range of motions.