Partial knee replacement

A partial knee replacement resurfaces only the part of the knee that is worn out, leaving the healthy cartilage, bone, and ligaments in place. The knee has three compartments — the inner side, the outer side, and the area behind the kneecap — and a partial replacement may be an option when arthritis is limited to one of them.

A partial knee replacement may be discussed when knee arthritis symptoms persist despite non-surgical care and the pain is concentrated in one area. Typical signs include:

• Pain focused on the inner or outer side of the knee, or behind the kneecap
• Pain with walking, stairs, or standing that limits daily activities
• Swelling and stiffness that keep returning
• Too little relief from exercise, medication, injections, or bracing

Pain spread across the whole knee usually points to arthritis in more than one compartment, where a total knee replacement is more often recommended.

Most partial knee replacements are done for osteoarthritis that has worn down one compartment, often the inner side of the knee.

A partial replacement is usually not a good fit for people with inflammatory arthritis such as rheumatoid arthritis, arthritis in more than one compartment, significant stiffness, or damaged knee ligaments.

Deciding whether a partial replacement suits your knee starts with where the pain is, a careful examination of motion, alignment, and ligament stability, and X-rays, sometimes taken in special positions to show each compartment. An MRI is used in some cases.

The final decision is confirmed during the operation. If the surgeon finds more widespread damage than imaging showed, a total knee replacement may be done instead; this backup plan is discussed with you before surgery.

Non-surgical treatment for knee arthritis — strengthening exercise and physical therapy, weight management when appropriate, medications, a brace or walking aid, and injections — comes first and may control symptoms for a long time.

In a partial knee replacement, the surgeon removes the damaged cartilage and a thin layer of bone from one compartment, places metal implants on the thighbone and shinbone (held with cement or press-fit), and inserts a plastic spacer between them. The rest of the knee is left as it is.

Compared with a total knee replacement, a partial replacement is a smaller operation with less blood loss and may allow a quicker early recovery, and some people feel the knee moves more naturally. The trade-offs are that arthritis can later develop in the parts of the knee that were not replaced, and long-term studies suggest partial knee implants may not last as long as total knee implants; either can lead to further surgery, often conversion to a total knee replacement. Risks of the operation itself are similar to those of knee replacement in general, including infection, blood clots, and stiffness. Your surgeon will help you weigh these factors for your knee.

Many people go home the same day or the next day and put weight on the leg right away, using a walker, crutches, or cane for a short time. Physical therapy helps restore motion and strength. Recovery generally involves a gradual return to daily activities over the following weeks, guided by your surgeon and therapist.