Author: Christopher N. Walton, M.D.
Date: 05/01/2009

Total joint replacement is a common, successful surgery for patients with degenerative arthritis. However, patients who have arthritis in a limited area of the knee may be candidates for a partial knee replacement, which is also known as a unicompartmental arthroplasty (UKA). A UKA involves smaller incisions, a quicker recovery, and a more normal feeling knee when placed in the appropriate patient. As with total knee replacements, unicompartmental arthroplasty may be recommended for patients who have not yet achieved pain relief with medical management, strengthening exercises or weight loss.

The knee has three compartments. The medial compartment on the inside, and the lateral compartment on the outside of the knee. The area behind the kneecap in the femur is called the patellofemoral joint. With the UKA, the surgical procedure resurfaces or replaces only the affected area of the knee. It preserves the remainder of an otherwise healthy knee, including the knee ligaments.

In general, the principal criteria determining who is a candidate for a unicompartmental arthroplasty includes: 1) arthritis confined to a specific compartment of the joint; 2) intact ligaments (specifically the ACL); 3) non-inflammatory arthritis; 4) not morbidly obese; and 5) a relatively light to sedentary activity or lifestyle.

The recovery after surgery from the unicompartmental arthroplasties is usually much quicker than a total knee arthroplasty. Patients in general have less pain and a quicker recovery to normal walking, including discontinuing assisted aids sooner. In addition, they generally achieve more normal motion. The hospitalization with an unicompartmental arthroplasty is often two days or less as opposed to three to four days for a standard total knee replacement.

Since first performed in the 1970's, unicompartmental arthroplasty has greatly improved, resulting in increased popularity with both patients and orthopedists. The operation generally is completed in one hour's time.

During the surgical procedure, the damaged bone is removed and replaced with an implant made of metal components on both the femur and tibia followed by a plastic insert. There are several types of plastic inserts, those that snap into the metal and those that "float" along the surface between the two metal components. The implants are cemented at the time of surgery, so the patient is able to stand the day of surgery.

Most patients go home the second day after surgery with steadily improving range of motion. Walking, swimming, and biking after surgery are very acceptable. High impact activities, jogging, running and jumping are generally discouraged.

Current success rates for unicompartmental arthroplasty shows a 92 percent survival at 15 years. Over the past year, I have performed 50 partial knee replacements. I do one to two partial replacements a week. Many of my patients are walking unassisted within three to four weeks of their surgeries.

Finally, the question "How long do they last?" Unicompartmental arthroplasty has recently shown increased survivorship for longevity. An attractive feature of the partial knee replacement is that it can be converted to a total knee replacement relatively easily if need be. Overall the unicompartmental arthroplasty has expanded our ability to treat arthritis on an individual basis.