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Unicompartmental Knee Replacement

A unicompartmental knee replacement is sometimes used instead of a total knee replacement when only one side of the knee has been damaged by osteoarthritis.

Arthritis Desc.

Unicompartmental knee replacements involve smaller incisions, less bleeding, quicker recovery, and less bone loss than a total knee replacement.

The prosthesis does not interfere with existing ligaments, tendons, or nerves. You retain normal balance and the natural stability of the healthy half of your knee joint and your own tendons and ligaments. Your kneecap is left in place, enabling you to regain much of the strength in your quadriceps.

Preparing for Surgery

The decisions you make and the actions you take before your surgery can be every bit as important as the procedure itself in ensuring a healthy recovery. Getting a second opinion from a surgeon who is as qualified as the surgeon who gave the initial diagnosis is usually recommended.
  • Make sure you have received any equipment you will need when you get home from the hospital. This may include crutches, ice packs or coolers, or a continuous passive motion (CPM) machine. You should receive prescriptions for any of these from your doctor when your surgery is scheduled.
  • Understand the potential risks and benefits of the surgery, and ask your surgeon any questions that will help you better understand the procedure. It can also help to talk to someone else who has undergone the same surgery.
  • Before surgery, notify your physician of any physical problems you have been experiencing, such as a fever or infection. You should also notify your surgeon of any medication you are taking.
  • Practice walking with your crutches in case you need to use them after surgery.
Make sure the orthopedist performing the surgery is board-certified, which can be determined by calling the American Board of Orthopaedic Surgery at 919-929-7103.

Day Of Surgery

At most medical centers, you will go to "patient admissions" to check in for your inpatient unicompartmental knee replacement procedure.

After you have checked in to the hospital or clinic, you will go to a holding area where the final preparations are made. The paperwork is completed and your knee area may be shaved (this is not always necessary). You will wear a hospital gown and remove all of your jewelry.

You will meet the anesthesiologist or anesthetist (a nurse who has done graduate training to provide anesthesia under the supervision of an anesthesiologist). Then, you will walk or ride on a stretcher to the operating room. Most patients are not sedated until they go into the operating room.

Here are some important steps to remember for the day of your surgery:
  • You will probably be told not to eat or drink anything after midnight on the night before your surgery. This will reduce the risk of vomiting while you are under general anesthesia.
  • Arrange for someone to drive you home when you are released, usually within one to three days after surgery.
  • Wear a loose pair of sweatpants, preferably with a zipper on the side, or shorts that will fit comfortably over your knee bandage and brace when you leave the hospital.
Take it easy. Keeping a good frame of mind can help ease any nerves or anxiety about undergoing surgery. Distractions such as reading, watching television, chatting with visitors, or talking on the telephone can also help.


During a unicompartmental knee replacement, surgeons reshape bones on one side of your knee. Metal and polyethylene components that mimic the shape and function of a normal knee are then attached to the ends of your shinbone (tibia) and thighbone (femur). The procedure usually takes about one-and-a-half hours to perform.

A unicompartmental knee replacement requires the removal of about a quarter inch of bone. A total knee replacement can still be performed in the future if arthritis damages the other side of your knee.

  • After anesthesia is administered, which may be regional, or general, the surgical team sterilizes the leg with antibacterial solution.
  • A three-inch incision is made down the front of the knee, exposing the ends of the shinbone and thighbone.
  • On the damaged side of your knee, a quarter-inch piece of bone is removed from the bottom of your thighbone to expose the top of your shinbone.
  • Damaged cartilage and meniscus (the main cartilage pad in the center of your knee) are removed from the top of the shinbone on one side of your knee.
  • The top of your shinbone is flattened and reshaped to fit the prosthetic shinbone part. The plastic shinbone (tibial) component is cemented in place.
  • The damaged area on the bottom of your thighbone is removed and reshaped to fit the metal thighbone (femoral) part. The metal piece is cemented in place over the thighbone.
  • Surgeons test the function of the new prosthetic pieces by bending the knee. The layers of tissue in your knee are stitched together and you are taken to the recovery room.

Recovery Room

Following a unicompartmental knee replacement, you usually stay in the recovery room for at least two hours while the anesthetic wears off.

You will be given pain medicine, either orally or through an IV (intravenous) line, as well as instructions for what to do over the next couple of days. Your knee will be bandaged and may have ice on it. You may have significant pain early on and you should take the pain medicine as directed. Remember that it is easier to keep pain suppressed than it is to treat pain once it becomes present, so ask the nurse for medication when you feel pain coming on.

You should try to move your feet and ankles while you are in the recovery room to improve circulation.

Your temperature, blood pressure, and heartbeat will be monitored by a nurse, who, with the assistance of the doctor, will determine when you are ready to leave the recovery room.

Most patients remain in the hospital for one or three nights following a unicompartmental knee replacement.

Post-Op In Hospital

After a unicompartmental knee replacement, you usually are taken to a hospital room where the medical staff can regularly monitor your recovery.

To prevent the knee joint from stiffening after surgery, your operative knee may be placed in a continuous passive motion (CPM) machine. The CPM machine is attached to your bed, and moves your knee through a continuous range of motion. There will likely be pain, and you can expect to be given pain medication as needed. Ice also helps control pain and swelling.

If you have a heart condition, you may be taken to the ICU (intensive care unit) for routine cardiac monitoring.

For two or three days after surgery, you may experience night sweats and a fever of up to 101. Your physician may suggest acetaminophen, coughing, and deep breathing to get over this. This is common and should not alarm you.

You will be given a prescription for pain medication and schedule a series of follow-up visits sometime around one week, one month, and three months after surgery.

The incision usually starts to close within six days. Physicians may fit you with a brace that allows a limited range of movement.

You may be able to bear weight on your knee when released from the hospital. But some patients may need to use crutches for a few days until they are comfortable walking on their new knee.

Your physician and physical therapist will help you learn to balance on the new knee and let you practice unaided walking and going up and down stairs before you leave the hospital.

Recovery at Home

You may feel pain or discomfort for the first week at home after a unicompartmental knee replacement, and you will be given a combination of pain medications as needed. A prescription-strength painkiller is usually prescribed and should be taken as directed on the bottle. Taking one every four to six hours as directed is a good idea during the first few days to suppress pain.

Swelling in your knee usually slowly decreases over a span of two to three weeks after surgery. There may be some minor bleeding for a few days, but by the time you are released from the hospital, most bleeding should have stopped. If you notice swelling or bleeding increase, you should call your physician. Physicians generally recommend that you avoid activities that place stress your knee for about two weeks, so that the bones and cartilage can heal around the implant. Light walking and stretching can usually start immediately after surgery.

Here is what you can expect and how you can cope after an unicompartmental knee replacement:
  • Icing your knee for 20 or 30 minutes a few times a day during the first week after surgery will help reduce pain.
  • Keep your knee elevated above heart level as much as possible to reduce swelling and pain. Place pillows under the ankle of the operative leg while you are in bed.
  • Range of motion exercises are important for healing. Regaining full extension is just as important as bending your knee until you get your stitches or staples removed.
  • To help speed healing, keep your incision dry for seven to ten days. A plastic shower bag can help keep the incision dry while bathing. You can purchase these bags at a pharmacy or surgical supply store. Wait until you can stand comfortably for 10 or 15 minutes at a time before you take a shower without assistance.
  • Crutches or a cane may be needed for about two weeks, depending on the pain. Older patients may have to continue using crutches or a cane for a longer period of time.
Most patients can resume normal daily activities, driving, and light exercise, like swimming and cycling, within two weeks after surgery.


Most patients can begin physical therapy immediately after surgery. In the first few weeks of rehabilitation, your physical therapist usually helps you stretch the muscles in your hamstrings, quadriceps, and calves while flexing and extending your knee to restore a full, pain-free range of motion.

Aerobic Exericse

When pain has decreased, physicians generally recommend at least 30 minutes of low-impact exercise a day for patients with arthritis. You should try to cut back on activities that place added stress on your knees, like running and strenuous weight lifting.

Cross-training exercise programs are commonly prescribed when you have arthritis. Depending on your preferences, your workouts may vary each day between cycling, cross-country skiing machines, elliptical training machines, swimming, and other low-impact cardiovascular exercises. Walking is usually better for arthritic knees than running, and many patients prefer swimming, which takes your body weight off your knees and makes movement easier.

Once your physical therapist has taught you a proper exercise program, it is important to find time each day to perform the prescribed exercises.


Strength training usually focuses on moving light weights through a complete, controlled range of motion. You should generally avoid trying to lift as much as possible with your quadriceps and hamstrings. Your physical therapist typically teaches you to move slowly through the entire movement, like bending and straightening your knee, with enough resistance to work your muscles without stressing the bones in your knee.

Once your physical therapist has taught you a proper exercise program, it is important to find time each day to perform the prescribed exercises.

The Knee Society Office:
9400 W. Higgins Rd., Suite 500, Rosemont, IL 60018-4976
Telephone: (847) 698-1632 Fax: (847) 823-0536
Email: knee@aaos.org