Advantages of Partial Knee Replacement

Multiple studies have shown that modern unicompartmental knee replacement performs very well in the vast majority of patients who are appropriate candidates.

The advantages of partial knee replacement over total knee replacement include:

• Quicker recovery
• Less pain after surgery
• Less blood loss

Also, because the bone, cartilage, and ligaments in the healthy parts of the knee are kept, most patients report that a unicompartmental knee replacement feels more "natural" than a total knee replacement. A unicompartmental knee may also bend better.

Disadvantages of Partial Knee Replacement

The disadvantages of partial knee replacement compared with total knee replacement include slightly less predictable pain relief, and the potential need for more surgery. For example, a total knee replacement may be necessary in the future if arthritis develops in the parts of the knee that have not been replaced.

In a partial knee replacement, only the damaged compartment is replaced with an artificial device.

Medical History

Your doctor will ask you several questions about your knee pain. He or she will be specifically concerned with the location of your pain. If your pain is located almost entirely on either the inside portion or outside portion of your knee, then you may be a candidate for a partial knee replacement. If you have pain throughout your entire knee or pain in the front of your knee (under your kneecap) you may be better qualified for a total knee replacement.

Physical Examination

Your doctor will closely examine your knee. He or she will try to determine the location of your pain. Your doctor will also test your knee for range of motion and ligament quality. If your knee is too stiff, or if the ligaments in your knee feel weak or torn, then your doctor will probably not recommend unicompartmental knee replacement (although you still may be a great candidate for total knee replacement).

Imaging Tests

Your doctor will order several x-rays of your knee to see the pattern of arthritis. Some surgeons may also order a magnetic resonance imaging (MRI) scan to better evaluate the cartilage.

Good candidate for partial knee replacement. (Left) In this x-ray, the lateral compartment has a normal joint space, and the medial compartment has severe arthritis with "bone-on-bone" degeneration. (Right) The same knee after partial knee replacement.

Not a candidate for partial knee replacement. (Left) This x-ray shows severe arthritis in both the medial and lateral compartments. This patient is a good candidate for total knee replacement, as shown in the x-ray on the right.

Before Surgery

You will likely be admitted to the hospital on the day of surgery.

Before your procedure, a doctor from the anesthesia department will evaluate you. He or she will review your medical history and discuss anesthesia choices with you. You should also have discussed anesthesia choices with your surgeon during your preoperative clinic visits. Anesthesia can be either general (you are put to sleep) or spinal (you are awake but your body is numb from the waist down).

Your surgeon will also see you before surgery and sign your knee to verify the surgical site.

Surgical Procedure

A partial knee replacement operation typically lasts between 1 and 2 hours.

Your surgeon will make an incision at the front of your knee. He or she will then explore the three compartments of your knee to verify that the cartilage damage is, in fact, limited to one compartment and that your ligaments are intact. If your surgeon feels that your knee is unsuitable for a partial knee replacement, he or she will instead perform a total knee replacement. He or she will discuss this contingency plan with you before your operation to make sure that you agree with this strategy.

If your knee is suitable for a partial knee replacement, your surgeon will use special saws to remove the cartilage from the damaged compartment of your knee and will cap the ends of the femur and tibia with metal coverings. The metal components are generally held to the bone with cement. A plastic insert is placed between the two metal components to allow for a smooth gliding surface.

After the surgery you will be taken to the recovery room, where you will be closely monitored by nurses as you recover from the anesthesia. You will then be taken to your hospital room.