A partial (tibiofemoral) knee replacement can be performed to either the medial or lateral compartment using a relatively small incision preserving the cruciate ligaments, retaining the patella and allowing a quick recovery and reliably good range of motion.
The medial or inner most compartment of the knee is the most commonly worn and symptomatic part of the human knee. The medial compartment will often develop a pattern of wear and tear affecting the front (anterior) and inside (medial) most aspect with associated pain, swelling and stiffness. If the patient has an intact anterior cruciate ligament (ACL) and reasonable preservation of their flexibility (knee bending – range of motion) and cartilage in the lateral and patellofemoral compartments, they may be suitable for a medial unicompartmental knee replacement (UKR) rather than a total knee replacement (TKR). Approximately 1 in 4 patients who are being considered for knee replacement surgery are suitable for a UKR rather than a TKR. Patients with arthritis in the lateral or outermost compartment of the knee, relatively good cartilage on the medial and patellofemoral compartments, intact anterior cruciate ligament (ACL) and reasonable preservation of their knee bending (range of motion), also may be a candidate for a lateral unicompartmental knee replacement (UKR) rather than total knee replacement. Whilst isolated arthritis in the lateral compartment is not common, patients who have previously injured the lateral compartment or torn their lateral meniscal cartilage are at risk for developing this condition. The most successful and commonly used implant in Australia for partial knee replacement has been the Oxford UKR, which has a mobile bearing, and several potential advantages to most fixed bearing UKR devices, including lower wear rates, lower revision rates, greater range of motion and more natural movement. The ACL contains important nerve fibres used for “proprioception” or position sense and as it is preserved with the Oxford UKR, allows patients to walk over unsteady ground or in poorly lit conditions and also to change direction with more confidence than those patients without an ACL, which is a distinct advantage over other knee replacements that sacrifice it including TKR’s. A recent development in the design of the lateral Oxford UKR included a more natural contour matching tibial component with a domed or convex shape and a biconcave meniscal polyethylene mobile bearing. This has helped to address one of the historical concerns with a lateral Oxford UKR of a higher bearing dislocation rate, which now approximates the lower dislocation rate of the medial Oxford UKR. Patients who engage in recreational social sports where sudden changes in direction are important such as golf, skiing, surfing and tennis are thus better able to do so with a UKR than a TKR.
The Medial Oxford UKR is performed through a minimally invasive surgery (MIS) technique with a small (6-7cm) incision, and the Lateral Oxford UKR is performed through a slightly longer (7-8cm) incision, and only replaces the worn areas of cartilage on one side of the femur and tibia with two small metallic implants and a mobile plastic bearing which is inserted in between these components. The lateral and patellofemoral compartments are left intact in the medial UKR and the medial and patellofemoral compartments left intact in the lateral UKR as are also the cruciate and collateral ligaments and the surrounding muscles including the quadriceps, and because of this there is significantly less blood loss, shorter hospital stay, lower infection rates and other complications such as deep vein thrombosis (DVT) and pulmonary embolism (PE) are also significantly lower. Patients usually only require a two night stay in hospital following a UKR, as compared to a four to seven night stay following a TKR, and generally are able to mobilise without walking aids after one week. Most patients will use strong analgesia for two to four weeks and anti-inflammatories for two to three months and are usually able to resume most normal day to day activities within the first four to six weeks. Recreational activities (walking for fitness, cycling and swimming etc) can usually commence after six weeks, and more vigorous activities (golf, tennis, surfing) after two to three months. Whilst most UKR patients will be walking fairly freely after three or four weeks, and feel like they are able to drive a car, it is a legal recommendation for insurance purposes, that patients who have undergone knee replacement surgery do not drive a motorised vehicle (car, motorbike, truck etc) for a six week period. Returning to work duties is generally possible for clerical type jobs within 3 to 4 weeks, and sooner for some, depending upon the individual’s mobility, analgesia requirement and job demands. Most knee replacements are likely to last for 10-15 years, so depending upon the age and health of the patient at the time of their initial knee replacement procedure (regardless of whether it is a total or partial knee replacement), there is a high likelihood that they will outlast their first knee replacement. Most Oxford UKR’s if performed using prescribed technique, are quite bone conserving, and when ready for revision, can simply be converted to a normal or primary TKR. Thus one of the additional benefits of having a UKR as your first knee replacement, is that your next knee replacement will still usually only be a primary (normal) TKR which should then last for another 10-15 years, meaning that between these two implants, patients usually will have 20 -30 years before needing to be considered for a more complex revision (stemmed) TKR.