Unicompartmental knee arthroplasty (UKA) is surgery to replace either the inside (medial) or outside (lateral) compartments of the knee.

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

See also: Total knee replacement

You may receive either general anesthesia (asleep, no pain) or local anesthesia (awake but no pain). The surgeon will make a small cut about 3 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 - 1 1/2 hours.

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 - 3 times smaller than the one required for 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:

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

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:

• Are obese
• Engage in heavy work or sports
• Have significant ligament problems

Risks for anesthesia include:

• Problems breathing
• Reactions to medications

Risks for any surgery include:

• Bleeding
• Infection

Risks for UKA include:

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

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.