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

Because only one 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; Minimally invasive partial knee replacement

Partial knee replacement surgery involves removing damaged cartilage and bone in the knee joint. Man-made (artificial) pieces called prostheses are then placed in the knee.

You will not feel any pain during surgery because you will receive anesthesia, medicine that blocks pain. You will have one of these two types of anesthesia:

• General anesthesia. This means you will be unconscious and unable to feel pain.
• Regional ( spinal or epidural) anesthesia. Medicine is put into your back to make you numb below your waist. You will also get medicine to make you sleepy if you have this type of anesthesia.

After you receive anesthesia, your surgeon will make a surgical cut over your knee to open it up. This cut is often 3 to 5 inches long. Then your surgeon will:

• Examine the whole inner knee area. If damage is found in more than one part of your knee, you may need a total knee replacement. Most of the time, however, this is not needed.
• The damaged bone is removed and replaced with an implant (prosthetic) that is made of plastic and metal.
• The ends of the thigh and shin bone will be cut and 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 most common reason to have a knee joint replaced is to relieve severe arthritis pain. Your doctor may recommend knee joint replacement if:

• You are having symptoms of knee arthritis, such as:
  • You are unable to sleep through the night because of knee pain
  • Your knee pain prevents you from preparing meals, bathing, walking, doing household chores, or performing other daily activities
• Your knee pain has not improved with other treatments (medicine, injections, and physical therapy)
• You understand what surgery and recovery will be like

Knee joint replacement is usually done in people age 60 and older. Younger people who have a knee joint replaced may put extra stress on the new knee joint and cause it to wear out.

Most people with knee arthritis have a surgery called a total knee arthroplasty (TKA). Partial knee arthroplasty may be a good choice for people who have arthritis on only one side of the knee, and who:

• Are older, thin, and not very active
• Do not have very bad arthritis on the other side of the knee or under the kneecap (patella)
• Have only minor deformity of the knee
• Still have good range of motion in the knee

Risks for anesthesia include:

• Problems breathing
• Reactions to medications

Risks for any surgery include:

• Bleeding
• Infection

Risks for UKA include:

• Blood clots
• 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 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.
• Practice using a cane, walker, crutches, or a wheelchair, especially the correct ways to:
  • Get in and out of the shower
  • Go up and down stairs
  • Sit down to use the toilet and stand up after using the toilet
  • Use the shower chair

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 right away. There is usually less rehabilitation or physical therapy needed 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 fast recovery and have much less pain than they did before surgery.

Many patients are able to walk without a cane or walker by 1 - 2 weeks after surgery. You will need physical therapy for 4 to 6 months.

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

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.

Richmond J, Hunter D, Irrgang J, et al. American Academy of Orthopaedic Surgeons. Treatment of osteoarthritis of the knee (nonarthroplasty). J Am Acad Orthop Surg. 2009;17:591-600.