Femur-First Cut Kinematically Aligned Unicompartmental Knee Arthroplasty: A Seamless Surgical Technique from UKA to TKA

Kinematic alignment (KA) is based on a resurfacing philosophy that restores the patient's native joint line orientation and preserves physiological soft-tissue balance. In calipered KA total knee arthroplasty, reconstruction of the distal femoral articular surface is the first and most critical step because it establishes the cylindrical axis that governs knee kinematics. Although unicompartmental knee arthroplasty (UKA) shares the same resurfacing philosophy, most currently available techniques begin with tibial resection, making femoral component positioning dependent on tibial alignment, gap balancing, and implant thickness. This may reduce the reproducibility of femoral component orientation and differs conceptually from established calipered KA principles. This Technical Note describes a femur-first calipered kinematically aligned technique for fixed-bearing medial UKA. The procedure reconstructs the distal and posterior femoral articular surfaces before tibial preparation using caliper verification of bone resections. Tibial resection is subsequently performed independently to reproduce the native posterior tibial slope while preserving physiological ligament tension throughout the range of motion. The described workflow follows the established principles of calipered KA while remaining applicable to fixed-bearing UKA. By establishing femoral anatomy before tibial preparation, this technique provides a reproducible and anatomically consistent resurfacing strategy and may facilitate intraoperative conversion to total knee arthroplasty when necessary.