1) What is it?
Knee replacements can be classified in several ways.

One way is according to the portion of the knee replaced. For example one portion can be replaced (unicompartmental), or two (bicompartmental) or three (tricompartmental). Therefore a unicompartmental knee replacement is a resurfacing or replacement of one compartment of the knee. It is just one of surgical options for the treatment of osteoarthritis of the knee.

2) History/Background
The idea of replacing one portion of the knee is not a new concept. It has been studied and performed since the 1970's.

Though it developed at the same time as total knee replacement, the procedure has taken time to gain widespread acceptance in the orthopaedic community. This was in part due to early reports of poor results after the procedure.

However, further review of these studies shows that those poor results may be attributed to patient selection, the type of artificial component used, and surgical technique. Identification and correction of pitfalls in the surgical technique plus the development of better implant designs have renewed enthusiasm for unicompartmental replacement in certain selected patients.

3) What are the indications for Unicompartmental Knee Replacement?
Every person's case is different so you should discuss what is right for you with your orthopaedic surgeon. But here are the general indications that we use for patients who undergo an unicompartmental replacement:

Indications for Unicompartmental Replacement

• Pain with weight bearing on one side of the knee
• X-ray showing narrowing at predominately one side of the joint (see x-ray above of knee with joint space narrowing)
• Failure to respond to non-operative care or operative efforts at cartilage treatment (repair, replacement, or regeneration of articular cartilage)
• Relative Contraindications to the Procedure
• Inflammatory arthritis like rheumatoid arthritis, lupus arthritis, psoriatic arthritis, arthritis inflammatory bowel disease
• Severe curvatures of the legs like severe bowleg or knock-knee. For correction of bowlegs see "osteotomy."

Patients usually stay in the hospital for one or two nights. Full weight bearing is permitted immediately. Patients are instructed in specific exercises and practice going up and down stairs before leaving the hospital.

Upon leaving the hospital, patients return directly to our Clinic for exercise training. The exercises depend on the age and activity level of the patient and are customized to that patient¹s abilities. Most patients can start with pool exercises and bicycling exercises two weeks after leaving the hospital.

Out-of-town patients can usually return home seven to ten days after surgery. Normal follow-up appointments may vary depending on the case but usually are at 1 week, 1 month, and 3 months after surgery.

5) What sports can I return to and when?
At The Stone Clinic our goal is to return the patient fitter, stronger and faster and with significantly less pain than they were before they presented or than before they were injured if possible. We permit our patients with unicompartment knee replacements to play all sports including tennis, skiing, golfing, and bicycling. In general, as with any artificial component, the less impact, the longer the component will last. Therefore, we prefer the non-impact sports in preference to running or jumping type activities. Return to sports is permitted as soon as the muscle strength has returned to a level that permits a near normal gait.

6) What are the complications associated with unicompartmental replacement?
All surgery that involves artificial components has the risks of loosening, wearing out, infection, mal-position, loss of motion, and scar tissue formation. The surgery has the risks of bleeding, blood clot formation, and injury to nerves and vessels, all of which can result in the most severe cases in loss of the limb or life. Fortunately, these risks are relatively small but should be considered in making your decision. The most recent data suggests that artificial knee joint components should have a life span between ten and twenty years. The components can be replaced if they wear out. However, in general, the best results come from the first operation. 

7) A few other commonly asked questions:
Will the joint set off the metal detectors at the airport?
    - No.

Do I have to take antibiotics when I have my teeth cleaned?
    - Not after the second year is the current recommendation. Probably not at all, but there might be an increased risk during the initial healing phase; though this is not well established.

Will the pain go away?
    - Usually all the medial pain is gone the day after surgery.

Will I have normal knee motion?
    - Usually motion obtained after unicompartmental surgery is from 0 degrees (straight leg) to 115-125 degrees of bending. However, people and knees vary.

8) What is the rehabilitation protocol?

References

• Grelsamer RP. Unicompartmental osteoarthrosis of the knee. Journal of Bone and Joint Surgery-American Volume.77(2):278-92, 1995 Feb.
• Thornhill TS. Scott RD. Unicompartmental total knee arthroplasty. Orthopaedic Clinics of North America. 20(2):245<56, 1989 Apr.
• Wilcox PG. Jackson DW. Unicompartmental knee arthroplasty. Orthopaedic Review. 15(8):490-5, 1986 Aug.

For more information:
B.J.'s Unicompartment Knee Replacement

Unicompartmental Knee Replacement Story