Surgical technique of robotic arm-assisted total knee arthroplasty via the lateral parapatellar approach for valgus knee deformity

BACKGROUND: Valgus knee deformity, which is less common, is not a mirror image of varus knee deformity and poses unique technical challenges in total knee arthroplasty (TKA). Although the lateral parapatellar approach may be advantageous for severe valgus knee, the medial approach is often preferred due to surgeons' limited familiarity with valgus TKA and the lateral approach. Recently, robotic technology has demonstrated superior accuracy in bone resection and soft-tissue balancing during TKA. Hence, we introduce the application of robotic technology for valgus knees via the lateral approach in TKA. As the standard patella drill template of the onlay oval patellar implant was designed for the medial approach, we created a reversed-asymmetric patella drill template for the lateral approach. In the recent cases, patellar tracking following prosthesis implantation was also evaluated using robotic technology. METHODS: We included cases of primary TKA performed for Ranawat classification types II and III with uncorrectable valgus knee alignment, as well as for valgus deformity > 20°. In TKA, arthrotomy was performed via the lateral approach, and the patella was retracted medially. After soft-tissue balancing was adjusted, bone resection was performed using the Mako robotic system. The patella was replaced with an onlay oval patellar implant using our novel patella drill template in the lateral approach. Patellar tracking on the femoral trochlear groove after implantation was visualized and assessed using robotic technology. RESULTS: The surgical procedures were performed smoothly in 10 knees of 9 patients. The pre-operative limitations of knee extension, Visual Analog Scale scores, and radiographic knee alignment significantly improved following TKA. Pre-operatively, the tibiofemoral joint gaps were tighter laterally in both extension and flexion; post-operative medial laxity was effectively corrected. The accuracy and precision of prostheses positioning were confirmed radiographically. Patellar tracking was found to be appropriate after replacement with the oval patellar implant. CONCLUSIONS: The combination of robotic assistance, the lateral approach, and onlay oval patellar implants using our originally developed patella drill template showed feasibility for precise bone resection, optimal soft-tissue balancing, and proper patellar tracking for TKA in cases of valgus knee deformity.