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Partial Knee Replacement


Total knee replacement surgery (“arthroplasty”) is performed with the aim of restoring function and reducing pain. This procedure is a good choice for patients with osteoarthritis. However, if osteoarthritis is in just a portion of the knee, a unicompartmental knee replacement (a “partial” knee replacement) may be more appropriate.


The red arrows above point to the medial, lateral, and patellofemoral compartments of the knee joint.

The three parts of the knee are: the medial compartment (on the inside portion of the knee), the lateral compartment (on the outside portion of the knee), and the patellofemoral compartment (the front of the knee between the kneecap and thighbone). Any one of these compartments may be the compartment that is replaced in a partial knee replacement.


Partial knee replacements are highly successful when performed in patients who are good candidates for the surgery. The relative advantages of partial knee replacements over total knee replacement include: faster recovery times with the potential for more mobility and a quicker recover with less pain and less blood loss.


Some disadvantages of the partial knee replacement are that more surgery may be required following this procedure and the pain relief is less predictable.


You may be a good candidate for surgery if non-surgical options are not reducing your symptoms or if you have advanced osteoarthritis. If the state of your knee is adversely affecting your daily life, you are likely a particularly good candidate for the procedure.

A partial knee replacement requires that only one compartment of your knee be damaged. Older patients with less active lifestyles are often great candidates for this procedure. However, in total, only about 7% of arthritic knee patients are good candidates for this particular intervention.

Above are illustrations of a bad candidate (on the left) and a good candidate (on the right) for partial knee replacement. The image on the left demonstrates that both the medial and lateral compartments of the knee is damaged, making partial knee replacement a bad option. However, the image on the right shows injury only in the lateral compartment, making it a good candidate for the procedure.

Above is a before image (left) and after image (right) of a good candidate for knee replacement. This x-ray shows that only the medial compartment of the knee was injured. Specifically, this compartment has severe arthritis with “bone-on-bone” degeneration.

The x-rays above show a knee that is not a good candidate for partial knee replacement because it has severe arthritis in both the medial and lateral compartments. This patient is thus a good candidate for total knee replacement.


When you arrive at the hospital for the procedure, you will be evaluated by a member of the anesthesia team. It will then be determined which form of anesthesia you will have for your procedure. It is likely that you will undergo general anesthesia, which puts you asleep during the procedure. However, you may have a spinal or epidural type of anesthesia, which would keep you awake during the procedure, but your legs would be numb. You will also get a nerve block, which is an injection that will reduce the pain you experience after the surgery.


The procedure should last about one or two hours. After Dr. Samimi makes an incision on the front side of your knee, he will explore all the compartments to verify that the damage is limited to just one compartment. If more than one compartment is damaged, he will perform a total knee replacement, as long as you have agreed to this contingency prior to the surgery.

If Dr. Samimi determines that he should do a partial knee replacement, he will employ special saws. He will then cap the bones with metal pieces. He will also insert plastic to help parts of the knee glide by one another seamlessly.

When the procedure is over, you will be monitored in a recovery room. Once you recover from your anesthesia, you will go to a hospital room.


A partial knee replacement is less invasive, so your stay in the hospital will be shorter for this procedure. Rehabilitation is also faster, with less pain and swelling. Patients can usually go home within three days of their operation.


The complication rate following knee replacements is low. Major complications are lower than 2% for total knee replacement and even lower for partial knee replacement. Blood clots are the most common complication, but there are ways to prevent this complication, which include elevating the leg, exercising the leg, using support stockings, and taking blood thinners.

It is possible that you will endure nerve or blood vessel injury or not regain a full range of motion. You should feel free to discuss any of these possibilities with your surgeon before surgery.


Stitches or staples will be placed along your wound and removed after a few weeks. Alternatively, sutures may be put beneath your skin on the front of your knee, which would not require removal. You should avoid getting your wound wet. Keep it sealed if you are exposed to water.


Do not be surprised if you don’t have much of an appetite during weeks following surgery. Try to maintain a balanced diet, and take an iron supplement if needed to promote proper tissue healing and to restore muscle strength.


It is essential that you exercise during the first few weeks after surgery. Within 3 to 6 weeks of surgery, you should be able to resume most normal activities. It is normal if you experience some pain with activity or at night. Your activity should include: resuming normal household activities, a graduated walking program, and specific exercises designed to increase the strength and mobility of your leg. You can begin driving once you can comfortably sit in the seat of a car.


Your knee may feel numb, especially around the incision, and you will likely experience stiffness when bending your leg. It is unlikely that you will regain full motion, and kneeling will likely be uncomfortable. However, kneeling is not harmful. You may feel some clicking of the metal and plastic while moving your knee, and your knee may activate metal detectors. For most patients, these differences in the knee become well-tolerated.


Following a partial knee replacement, you should engage in regular light exercise to increase the mobility and strength of your knee. You will, however, need to be cautious so that you do not endure further injury that could require more surgery. You should get a routine follow-up done about once a year. During these follow-ups, your doctor will likely image your knee to assess its status.

You also need to let your dentist know you’ve had a partial knee replacement and take antibiotics before any dental surgery you have at any time after the knee replacement.

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