One hundred-one knees with medial compartmental osteoarthrosis were treated by unicompartmental arthroplasty with the Oxford Knee. The strict selection criteria were: (1) the presence of functioning anterior cruciate ligament, (2) correctable deformity and (3) full thickness of articular cartilage in the lateral compartment. The mean elapsed time from surgery was 28 months. One knee required revision for a loose tibial component; one had meniscal bearing dislplacement 1 month after the operation and was revised succesfully by replacing the meniscal implant with a thicker one. One implant was revised to a tricompartmental prosthesis. The femoral component has a spherical articular surface. The meniscal bearing is made of high-density polyethylene and is concave superiorly and flat inferiorly to fit exactly the metal femoral and tibial components. The meniscal bearing is not attached to either metal component but is held in place by its reciprocal shape and the tension in the ligaments. The bearing, which is avaliable in nine thicknesses, is inserted after the metal components have been fixed, allowing the ligaments to be restored to their physiologic tension. No femoral component was radiographically loose. Loosening was observed in two cases only in the tibial component. There were radiolucent lines more than 2 mm thick around two other tibial components, involving less than 15% of the component’s surface in each case. In none of these cases was the leg misaligned. There was no radiographic evidence of disease progression in the lateral compartment of any joint and the Ahlback grades remained unchanged. All the patients were evaluated 2 years after surgery according to the Oxford Knee Score. Our scores ranged from 40 to 48. In our opinion medial unicompartmental arthroplasty is the appropriate treatment in approximately one third of patients undergoing surgery for osteoarthrosis of the knee. Key point of this operation is: the surgical technique is less invasive and preserves all the structures of the knee so that a short patient recovery time is allowed. Furthermore, unicompartmental implants cost less than tricompartmental prostheses and revision surgery is relatively easy if performed early and before extensive bone erosion has occurred.
