Unicompartmental Arthroplasty

What unicompartmental arthroplasty is

The knee is usefully thought of as three compartments: the medial compartment on the inner side, the lateral compartment on the outer side, and the patellofemoral compartment behind the kneecap. Arthritis does not always affect all three. In some knees the cartilage wears out in one compartment, most often the inner side, while the other surfaces remain in reasonable condition.

A unicompartmental replacement addresses only that worn compartment. A thin layer of damaged bone and cartilage is removed from the affected side of the joint and resurfaced with a small metal component and a plastic bearing, while the healthy cartilage in the other compartments, the kneecap surface and the cruciate ligaments inside the knee are preserved. Because the anterior and posterior cruciate ligaments are retained, the knee keeps more of its own mechanics than it does after a total replacement. The exposure required is smaller and less bone is removed, which is also why a partial replacement can generally be converted to a total replacement later if arthritis progresses in the remaining compartments.

Symptoms that often lead people to consider it

• Pain that is well localized to one side of the knee rather than felt throughout the joint
• Pain with walking, standing or stairs that has not settled with non-surgical care
• A knee that still bends and straightens reasonably well
• A leg that has begun to angle inward or outward, but is still correctable on examination
• An interest in an option that removes less bone than a total replacement

How it is evaluated

Candidacy for a partial replacement is more selective than for a total replacement, so evaluation focuses on confirming that the disease really is confined. Standing x-rays, including views that stress the knee or bend it, show how much cartilage space remains in each compartment. Examination assesses where the tenderness sits, how much motion the knee has, whether a deformity corrects when the knee is manipulated, and whether the cruciate and collateral ligaments are intact, since a deficient anterior cruciate ligament is an important consideration. MRI is sometimes used to look at the other compartments. Inflammatory arthritis, widespread cartilage loss or significant fixed deformity generally point away from a partial replacement.

Treatment options in general terms

Non-surgical care is generally tried first, and may include:

• Therapy and conditioning. Strengthening the muscles around the knee and low-impact activity.
• Unloader bracing. A brace intended to shift load away from the worn compartment.
• Medication and injections. Anti-inflammatory options and injection categories appropriate to arthritis pain.

If surgery is being considered, the alternatives that may be compared include:

• Unicompartmental replacement. Resurfacing one compartment, whether medial, lateral or patellofemoral.
• Osteotomy. Reshaping the shin or thigh bone to redirect load away from the worn side, an option that is mainly considered in younger, more active patients.
• Total knee replacement. Resurfacing the whole joint when more than one compartment is involved.

What to expect when you consult Dr. Wolfson

Dr. Wolfson is board certified in the United States and Canada and prefers to preserve a joint where that is a reasonable choice. A consultation reviews your imaging and examination to work out whether your arthritis is genuinely limited to one compartment, and covers what a partial replacement can and cannot address, including the possibility of later surgery if arthritis develops elsewhere in the knee. Second opinions are welcome.

This page provides general information about unicompartmental arthroplasty and is not medical advice. It is not a substitute for examination, imaging and diagnosis by a qualified physician. Every case is different and requires individual evaluation. If you have severe pain, an obvious deformity, loss of function, fever, or an injury from a significant accident, seek medical care promptly.

Contact Dr. Wolfson if you would like to setup an appointment. If you are a new patient, please book all in-person appointments with Dr. Wolfson via telephone.

If you live outside of the San Francisco Bay Area, you can request a complimentary phone consultation with Dr. Wolfson to assess your case. Please call or e-mail us to set up your complimentary consultation.

Call: (415) 221-4400

E-mail: [email protected]