Unicompartmental (or partial) knee replacement is an operation that has been around for over 40 years. First popularized in the 1970’s, these operations were used commonly before total knee replacement became popular. Some surgeons, however, have continued to use unicompartmental implants for certain patients in their practices.
The surgical procedure involves removing just a portion of the knee and resurfacing it with metal and plastic implants. The metal part resurfaces the femur or the upper bone and the plastic resurfaces the tibia or lower bone. Because only half (or part) of the knee is resurfaced, the rest of the knee must be in good shape prior to the surgery. Most people who develop osteoarthritis will tend to develop it in one part of the knee first and then have the disease progress to other areas of the knee. In fact, 85 percent of the people who develop osteoarthritis of the knee will have it involve the inner (medial) compartment primarily.
Patients with arthritis limited to one area of the knee are candidates for unicompartmental replacement. Of the patients I see with osteoarthritis of the knee, only 20 to 30 percent of those patients are candidates for a unicompartmental knee replacement. While the ideal patient for this procedure is over 60 years of age and has moderate activity level, the age range of my patients is from mid 30’s to 80, depending on disease type, amount of cartilage involvement, the degree of knee deformity, and status of the supporting ligaments.
The durability of unicompartmental knee replacements has been quite good with over 90 percent of the implants continuing to function well at 10 to 15 years after implantation. In some series, this has not been as good as the success with total knee replacement at 15 years and for this reason, many surgeons have elected not to use unicompartmental replacements in their practice. I have found that the advantages of a unicompartmental replacement are significant enough to accept a slightly higher risk of failure at 10 years. These advantages include less surgery, quicker rehabilitation, less blood loss, fewer immediate post-operative complications, and better range of motion for the knee. In addition, I have found that the patients who have a partial knee on one side and a total knee on the other will almost always prefer the partial knee replacement. If a unicompartmental knee fails, the knee can be repaired with a total knee replacement. This procedure is generally easier to perform than a revision of a failed total knee prosthesis.