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Unicompartmental knee arthroplasty (UKA) is minimally invasive surgery to replace one of the knee’s three parts (thighbone, shinbone, or kneecap) so that the knee works better.

Because only part of the damaged knee is replaced, it is often called a partial knee replacement.

See also: Total knee replacement

Partial knee replacement; Knee replacement - partial; Unicondylar knee replacement; Arthroplasty - unicompartmental knee; UKA

You may receive either general anesthesia (asleep, no pain) or local anesthesia (awake but no pain). The surgeon will make a small cut about three inches long over the knee that is damaged. The damaged bone is removed and replaced with an implant (prosthetic) made of plastic and metal. The thigh and shin bone may be slightly shaped to fit the implant. Once the implant is in the proper place, it is secured with bone cement, and the wound is closed with stitches.

The operation takes about 1 hour to 90 minutes.

UKA has gone under significant changes since first performed in the 1970s. Today, the procedure offers many benefits over total knee replacement, including:

• Smaller surgical cut. The cut used in UKA is about 2 to 3 times smaller than the one required by total knee replacement. A smaller cut means less blood loss, less tissue damage, and a faster recovery.
• Better range of motion after surgery.
• Shorter hospital stay.
• Cheaper procedure. UKA costs about half that of total knee replacement.
• If needed, the implant can be easily converted to a total knee replacement.

Pain relief is the same for both procedures.

Certain diseases and conditions can affect knee function. The most common reason for UKA is arthritis.

This procedure may be considered in patients with the following conditions:

• Osteoarthritis of the knee
• Knee deformity
• Refractory osteomalacia
• Avascular and aseptic necrosis

Patients age 60 and up who are not physically active and who have no history of inflammatory arthritis are good candidates for this procedure. UKA is not recommended for patients who engage in heavy work or sports, are obese, or have significant ligament problems.

Risks for anesthesia include:

• Reactions to medications
• Problems breathing

Risks for any surgery include:

• Bleeding 
• Infection

Risks specific to UKA include:

• Deep vein thrombosis
• Nerve and blood vessel damage
• Implant failure
• Reflex sympathetic dystrophy (rare)
• Fluid build-up in the knee joint
• Pain with kneeling

Most patients have a rapid recovery and have considerably less pain than they did before surgery. 

Most patients go home the day after surgery (unlike the 3 or 4 days required by a total knee replacement). You can put your full weight on your knee immediately. There is usually less rehabilitation or physical therapy required compared to total knee replacement.

Most forms of exercise are acceptable after surgery, including walking, swimming and biking. However, you should avoid high-impact activities such as jogging.

Berger RA, Meneghini RM, Jacobs JJ, et al. Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. J Bone Joint Surg Am. 2005 May;87(5):999-1006.

Patil S, Colwell CW Jr, Ezzet KA, et al. Can normal knee kinematics be restored with unicompartmental knee replacement? J Bone Joint Surg Am. 2005 Feb;87(2):332-8.