Pre-operative image of a 65-year-old male patient with progressively worsening right-sided knee pain that is localized to the inner aspect of the right knee. The knee X-ray demonstrates a focal area of osteonecrosis with full-thickness cartilage loss in the medial femoral condyle. The remainder of the knee is unaffected. The post-operative image shows the patient has now undergone a right unicompartmental knee replacement. The new partial knee implant resurfaces the damaged medial compartment while leaving the patient’s normal lateral and patellofemoral compartments intact.