![]() ![]() TKR constructs can accommodate keeping the posterior cruciate ligament (cruciate retaining) or not (cruciate sacrificing or posterior stabilised). In a ‘monobloc’ implant, the top of the tibia is replaced with a one-piece polyethylene or metal backed implant that is fixed directly to the bone. In a modular TKR construct, the polyethylene liner between the metal femoral and tibial components can be ‘fixed’ to the tibial component or ‘mobile’ with movement of the liner permitted on the tibial component. Surgeons and patients may choose from a range of implant components and combinations that make up knee replacement constructs, all with potential implications for how long a knee replacement will last. In UKR, these are retained in TKR, some of them are removed and their function compensated for by the implants used. Stability of the knee relies to a large degree on the ligaments in and around the knee. In both TKR and UKR, the remaining cartilage and some bone in the affected portion of the joint is removed and replaced, typically with implants made of metal fixed to the bone and polyethylene bearing surfaces between the metal implants or affixed directly to the bone. ![]() 1 In 2018, in the Swedish Knee Arthroplasty Register (SKAR), 90.0% of knee replacements were TKR and 9.6% UKR. In the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR), 87.4% of knee replacements performed in 2018 were TKR and 11% UKR. 6 Thus, many surgeons favour TKR as the first treatment for severe knee osteoarthritis. 1 Revision of UKR to TKR can be complex and may include treatment of bone defects. However, with time, osteoarthritis can develop in the other compartments, and a patient with a UKR is more than twice as likely to undergo revision than a patient who has had a TKR. 1 3 Compared with TKR, UKR surgery requires a less invasive procedure, retains more bone and native ligaments, the operation has a shorter duration, is quicker for patients to recover from and is cheaper for the NHS. Some surgeons favour UKR on the basis of radiographic evidence of osteoarthritis affecting a single medial or lateral compartment with estimates of patient eligibility for UKR as high as 48% of all people receiving knee replacement, 5 although actual rates of utilisation are around 10%. The patella that articulates with this may be resurfaced or not. In TKR, both the medial and lateral compartments are replaced as well as the trochlea (groove) on the front of the femur. Depending on which compartments are affected, a surgeon may perform a total knee replacement (TKR) or a unicompartmental knee replacement (UKR). The knee joint consists of three compartments: the medial femorotibial, the lateral femorotibial and the patellofemoral, all of which can be affected by osteoarthritis with associated pain and disability. ![]()
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