Functional positioning in robotic lateral unicompartmental knee arthroplasty: a step-by-step technique

Lateral unicompartmental knee arthroplasty (UKA) represents 1-2% of knee replacement procedures, yet offers distinct advantages including reduced surgical burden, bone stock preservation, and faster functional recovery. However, lateral UKA presents unique technical difficulties due to the surgical complexity of the lateral compartment. Recent advances in image-based robotic systems have demonstrated improved accuracy in implant positioning and promoted more individualized surgical strategies. This article presents a step-by-step surgical technique for lateral UKA using Functional Positioning (FP) principles in combination with an image-based robotic system. The technique ensures precise preoperative planning based on CT imaging, real-time intraoperative kinematic evaluation, and accurate component placement tailored to individual patient anatomy. The key steps of this surgical technique include comprehensive preoperative planning with 3D anatomical modeling, intraoperative kinematic evaluation following osteophyte removal, achieving centered femorotibial contact points throughout the full range of motion with precise lateral laxity gap boundaries, and cartilage mapping to ensure optimal component positioning and avoid overstuffing. FP addresses the characteristic posterior cartilage wear pattern of valgus knees while preserving pre-arthritic coronal alignment and avoiding varus overcorrection. This systematic approach demonstrates reproducible surgical steps that may translate into improved long-term outcomes and implant survivorship for lateral UKA procedures.