English

Abstract

Introduction Unicompartmental knee arthroplasty (UKA) is an effective surgical treatment for unicompartmental arthritis. Although results can be optimized with careful patient selection and use of a sound implant design, the most important determinant of success of UKA is component alignment. Studies have shown that component malalignment by as little as 2° may predispose to implant failure after UKA. Robot-assisted UKA has been projected to address this issue, which combines patient specificity and navigation. Modern-day robots overcome the problems with oldergeneration robots like iatrogenic fractures and also introduce in vivo dynamic assessment of the knee that incorporates soft tissue tension. Issues with learning curve, longer operating times and high cost investment persist. We discuss the technique of one such modern robotic design and review the literature with respect to accuracy in restoring limb alignment and their functional outcome. Conclusion Short-term results for robot-assisted UKA are promising, although long-term results are awaited to determine implant survivorship and functional outcome. Introduction Unicompartmental knee arthroplasty (UKA) can provide durable pain relief and functional improvement in greater than 90% of patients with focal arthritis or osteonecrosis of the medial or lateral compartments of the knee1. Concerns with UKA are early failure of the femoral2 or tibial3 components. The main cause of early failure is malpositioning of components with overcorrection or undercorrection of limb alignment. Swienckowski and Page reported that coronal malalignment of the tibial component beyond 3° predisposed to failure4. Malalignment of the femoral component has been found to cause femoral fracture5, patellar impingement and tibial component loosening6. In addition, excessive posterior slope (>7°) of the tibial component has been linked to tibial component loosening, anterior cruciate ligament (ACL) rupture7 and abnormal stress forces on the periprosthetic bone8. Therefore, though UKA has many benefits, technical difficulties in achieving accurate alignment have impeded widespread adoption of this procedure by orthopaedic surgeons. As many as 40% to 60% of components may be malaligned by more than 2° from the preoperative plan with conventional methods9,10. In a bid to improve UKA outcomes, orthopaedic surgeons have begun taking advantage of several technological innovations, including the use of computer-assisted navigation and robotics. Navigation has been shown to improve postoperative leg alignment over that obtained in conventional UKA10–12. Although navigation is a powerful visual aid, surgical outcomes still depend on the mechanical tools used in procedures. However, even with computer navigation, the number of outliers (beyond 2° of the preoperatively planned implant position) may approach 15%10. Recently developed robotic systems have tremendous potential to improve the outcomes of procedures such as UKA. Crucially, these new robots are ‘semi-active’; that is, the surgeon retains ultimate control of the procedure while benefiting from robotic guidance within target zones and surgical field boundaries. These zones and boundaries are determined by preoperative computed-tomography-based (CT-based) planning with continuous intraoperative visual feedback. The system incorporates navigation and robot technology. The combination allows for more accurate reproduction of the preoperative plan of implant placement, which may improve overall leg alignment and reduce iatrogenic morbidity9,13–15. The aim of this critical review was to discuss robot-assisted unicondylar knee arthroplasty.