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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 general anesthesia before this surgery. This means you will be unconscious and unable to feel pain. Or you may receive spinal or epidural anesthesia. Medicine is put into your back to make you numb below your waist.

Unicompartmental knee arthroplasty uses smaller surgical cuts than those required for a total knee replacement. The surgeon will make a small cut about 3 inches long over the knee that is damaged.

Next, the surgeon examines the entire inner knee area to determine the amount of damage. If there is a lot of damage, you may need a total knee replacement. Most of the time, however, this is not necessary.

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.

Your health care provider will usually try medicine, injections, and physical therapy for 6 months before considering surgery.

Your doctor may recommend this procedure if you have severe arthritis (osteoarthritis) in one side of one knee, which causes the following symptoms:

• Inability to sleep through the night because of knee pain
• Knee pain that does not improve with other treatments (medicine, injections, and physical therapy)
• Knee pain that limits or keeps you from being able to perform your daily activities, such as bathing, preparing meals, and doing household chores.

Your doctor may also recommend this procedure if you have:

• Avascular and aseptic necrosis
• Knee deformity
• Refractory osteomalacia

Risks for anesthesia include:

• Problems breathing
• Reactions to medications

Risks for any surgery include:

• Bleeding
• Infection

Risks for UKA include:

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

Always tell your doctor or nurse what drugs you are taking; even drugs, supplements, or herbs you bought without a prescription.

During the 2 weeks before your surgery:

• You may be asked to stop taking drugs that make it harder for your blood to clot. These include aspirin, ibuprofen (Advil, Motrin), naproxen (Naprosyn, Aleve), and other drugs.
• Ask your doctor which drugs you should still take on the day of your surgery.
• If you have diabetes, heart disease, or other medical conditions, your surgeon will ask you to see the doctor who treats you for these conditions.
• Tell your doctor if you have been drinking a lot of alcohol (more than one or two drinks a day).
• If you smoke, you need to stop. Ask your doctor or nurse for help. Smoking will slow down wound and bone healing. Your recovery overall may not be as good if you keep smoking.
• Always let your doctor know about any cold, flu, fever, herpes breakout, or other illness you may have before your surgery.
• You may want to visit a physical therapist to learn some exercises to do before surgery and to practice using crutches or a walker.

On the day of your surgery:

• You will usually be asked not to drink or eat anything for 6 - 12 hours before the procedure.
• Take the drugs your doctor told you to take with a sip of water.
• Your doctor or nurse will tell you when to arrive at the hospital.

Most patients go home the day after surgery. You can put your full weight on your knee immediately. There is usually less rehabilitation or physical therapy required compared to total knee replacement.

After surgery, you will be encouraged to do as much as you can for yourself. This includes going to the bathroom or taking walks in the hallways, always with someone helping you.

Most people do not need a short stay in a rehabilitation center after they leave the hospital and before they go home.

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

Many patients are able to walk without a cane or walker by 1 - 2 weeks after surgery.

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

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

Crockarell JR, Guyton JL. Arthroplasty of the knee. In: Canale ST, Beatty JH, ed. Campbell's Operative Orthopaedics. 11th ed. Philadelphia, Pa: Mosby Elsevier;2007:chap 6.

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;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;87(2):332-338.

Updated by: Dennis Ogiela, MD, Orthopedic Surgeon, Danbury Hospital, Danbury, CT. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.