Unicompartmental knee arthroplasty is a surgical procedure used to relieve arthritis in one of the knee compartments in which the damaged parts of the knee are replaced. UKA surgery may reduce post-operative pain and have a shorter recovery period than a total knee replacements.^[1] Also, UKA may have a smaller incision because the implants may be smaller.^[2]

In the United States, this procedure constitutes approximately 8% of knee arthroplasty.^[3]

Background

In the early 1950’s, Duncan C. McKeever figured that osteoarthritis could be isolated to only one compartment of the knee joint.^[4] As a result, the entire knee did not need to be replaced if only one knee compartment was affected.^[5] The UKA concept was designed to potentially have less trauma or damage than traditional total knee replacements by removing less bone and trying to maintain most of the patient’s bone and anatomy.^[6] Also, the concept was designed to have smaller implants that would keep most of the patient’s bone, which may help patients return to normal function faster.^[7]

Previously, UKA’s were not successful because the implants were poorly designed, proper patients were not selected, and the surgical technique was not optimal.^{[8] [9] [10] [11] [12]} Recent advancements have been made to improve the design of the implants.^[13] Also, picking the right patients was emphasized to make sure that the surgeons followed the indications and contraindications. Proper patient selection^[14], following the indications/contraindications, and performing the surgery well are key factors for the success of UKA.^[15]

Indications and Contraindications

UKA may be suitable for patients with moderate joint disease caused by painful osteoarthritis or traumatic injury, a history of unsuccessful surgical procedures or poor bone density that precludes other types of knee surgery.^[16] Patients that may not be eligible for a UKA include patients that have an active or suspected infection in or about the knee joint, may have a known sensitivity to device materials, have bone infections or disease that result in an inability to support or fixate the new implant to the bone, have inflammatory arthritis, have major deformities that can affect the knee mechanical axis, have neuromuscular disorders that may compromise motor control and/or stability, have any mental neuromuscular disorder, patients who are not skeletally mature, are obese^[17], have lost a severe amount of bone from the shin (tibia) or have severe tibial deformities, have recurring subluxation of the knee joint, have untreated damage to the knee cap and thigh bone joint (patellofemoral joint), have untreated damage to the opposite compartment or the same side of the knee not being replaced by a device, and/or have instability of the knee ligaments such that the postoperative stability the UKA would be compromised^[18].

The anterior cruciate ligament (ACL) should be intact.^[19] Although, this is debated by clinicians for patients that need a medial compartment replacement.