How to Deal with a Fixed-Bearing Medial Unicompartmental Knee Arthroplasty Implant?

The concept of unicompartmental knee arthroplasty was proposed by McKeever and MacIntosh in the 1950s and developed by Marmor in 1996. The surgical indication and preoperative planning are key factors to the procedure’s success, and an orthopaedic surgeon should know how to establish the indication and perform it correctly. The most important details are the imaging assessment, resection height, angle of inclination in the tibial section plane, and femoral distal and posterior cuts. The objective is to restore the initial deformity by correcting wear only. The tibial slope should be assessed preoperatively and restored at the end of the procedure. A medial parapatellar approach is used to expose the medial tibial plateau without releasing the medial collateral ligament. Tibial resection is performed to determine the amount of correction. The surgeon starts by placing the extramedullary cutting guide with the knee in 90° flexion to reproduce the physiological tibial coronal angle. A probe is then introduced into the section guide and the bottom of the bone cup to enable bone resection of the height planned preoperatively. The most important idea is that a good surgical indication, precise preoperative planning, and reliable placement technique are essential for good reproducible results in the medium and long terms. Twenty percent of knee replacements are unicompartmental knee arthroplasties. Based on Gérard Deschamps’s arguments, we also prefer an implant based on cuts rather than a resurfacing one. Since wear is mainly tibial, the use of resurfacing arthroplasty may risk lowering the articulation by an increase in femoral displacement.