[Unicompartimental joint (Oxford III) with mobile bearing : Minimally invasive implantation of a in the medial compartiment].

OBJECTIVE: Replacement of the joint surfaces in the medial compartment by an endoprothesis with a mobile bearing. INDICATIONS: Unicompartimental anteromedial gonarthrosis with an intact anterior cruciate ligament. Avascular necrosis at the medial femoral condyle. CONTRAINDICATIONS: Third to fourth degree cartilage damage in the lateral compartment. Lateral menisectomy. Symptomatic osteoarthritis in the femoropatellar joint. Chronic polyarthritis. More than 15° varus. Varus passive not redressable. Medial or lateral subluxation. More than 15° extension deficit. Passive flexion less than 110°. Cruciate ligament lesions with instability. Poor soft tissue conditions. SURGICAL TECHNIQUE: The leg is mounted on an electric leg holder that allows flexion up to 120°. The joint is opened via an anteromedial arthrotomy starting at the medial border of the patella and ending 3 cm below the tibia plateau. The osteophytes are resected and the tibial resection is performed with an oscillating saw under guidance of a jig which is positioned according to the physiological tibial slope. The medial collateral ligament must be protected with a Hohmann retractor. The vertical cut is performed first; then the horizontal cut is performed. The size of the resected plateau should allow space for a tibial component and a meniscus implant of 4 mm. The resected plateau seves to determine the size of the plateau. The jig for the femoral preparation is adjusted according to the axis of femur and tibia. After the posterior resection the 0 mm spigot is inserted into the central drill hole and the distal part of the condyle is milled. The depth of milling is determined by equalizing the flexion and extension gap. Extension and flexion gap balancing is controlled with test inlays. Posterior osteophytes at the medial femur condyle are cut with a special chisel. In the anterior aspect bone resection is needed to prevent impingement of the meniscus implant. Then the tibia plateau is finally prepared. After inserting the test implants the femoral and tibial components are cemented in one or two stages. POSTOPERATIVE MANAGEMENT: The patient is mobilised under full weight bearing with two crutches.
RESULTS: A total of 50 Oxford III hemiarthroplasties were implanted using the minimal invasive technique. Indication was an anteromedial gonarthrosis with intakt anterior cruciate ligament. Age varied between 59 and 79 years with a mean of 71 years. Follow-up was 5 years. There were three revisions till final follow-up. Cause was an inlay luxation in one case and in two cases with lateral arthrosis. The average KOOS score was 92.3 points (± 6 points).