A partial knee replacement removes and replaces only the damaged part of your knee

A partial knee replacement, also called a unicompartmental knee replacement, removes the cartilage and bone from one section of your knee joint and replaces it with an artificial implant. Your surgeon leaves the rest of your knee — including ligaments and the undamaged cartilage — intact. This is different from a total knee replacement, which removes cartilage and bone from all three compartments of the knee and replaces the entire joint surface.

The knee has three compartments: the inner (medial), outer (lateral), and kneecap (patellofemoral) areas. Partial replacement is an option only when arthritis or damage is confined to one compartment. If your damage spans multiple areas, your surgeon will recommend a total replacement instead.

The surgery takes about 60 to 90 minutes. Your surgeon makes a smaller incision than a total replacement requires, which means less tissue damage, less blood loss, and often a faster recovery. Hospital stay is typically one day or outpatient, depending on your surgeon's preference and your overall health.

Key Takeaways

  • A partial knee replacement replaces only the damaged compartment of your knee, leaving healthy cartilage and ligaments in place.
  • You are a candidate only if arthritis or damage is limited to one of the three knee compartments and your ligaments are stable.
  • Recovery is generally faster than total replacement because the incision is smaller and less tissue is disturbed.
  • Partial replacements may need revision to a total replacement later if arthritis develops in the other compartments.

Who is a candidate for partial knee replacement

Your surgeon will recommend a partial replacement only if specific conditions are met. The damage must be confined to one compartment — usually the inner compartment, which wears first. Your ligaments, especially the anterior cruciate ligament (ACL), must be intact and stable. If your ACL is torn or loose, a partial replacement will not work because the implant will shift and fail.

Age is not a barrier. Younger patients are sometimes better candidates because they are more active and place greater demands on the joint, and a partial replacement preserves more of the original knee structure. Older patients with limited activity may also be candidates if the damage is isolated.

Your surgeon will order X-rays and possibly an MRI to confirm that damage is limited to one compartment and that your ligaments are sound. If imaging shows arthritis in multiple compartments or ligament damage, a total replacement becomes the safer choice.

How a partial replacement differs from a total replacement

The main difference is scope: a partial replacement affects one compartment, while a total replacement replaces all three. Because less bone is removed in a partial replacement, the surgery is less invasive. The incision is smaller, blood loss is lower, and the hospital stay is often shorter or same-day.

Recovery time also differs. After a partial replacement, many people regain motion and strength within 6 to 12 weeks. After a total replacement, the timeline is often 3 to 6 months. Physical therapy is important after both, but the intensity and duration may be less demanding after a partial replacement.

One trade-off: a partial replacement does not address arthritis in the other compartments. If arthritis develops there later — which happens in some patients — you may need a second surgery to convert to a total replacement. A total replacement, by contrast, addresses all the damage at once and typically does not require revision for the same reason.

What to expect during recovery

Most people go home the same day or after one night in the hospital. You will wear a brace or compression sleeve and use crutches or a walker for the first week or two. Pain and swelling peak in the first few days and then decline steadily.

Physical therapy usually begins within a few days. Early sessions focus on regaining motion — straightening and bending the knee — and reducing swelling. As weeks pass, therapy progresses to strengthening exercises and walking without aids.

By 6 weeks, most people can walk without crutches and resume light activities like walking and swimming. Return to more demanding activities — hiking, tennis, or heavy lifting — typically takes 3 to 6 months. Your surgeon and physical therapist will guide you on when each activity is safe.

Potential complications and long-term outcomes

Partial knee replacements have good long-term outcomes overall. Studies show that 80 to 90 percent of implants last 15 to 20 years without needing revision. Complications are uncommon but can include infection, blood clots, stiffness, or implant wear.

The most common reason for revision is arthritis developing in one of the other compartments. This happens in roughly 10 to 20 percent of patients over 10 to 15 years, depending on age and activity level. When it occurs, your surgeon converts the partial replacement to a total replacement — a more complex surgery than the original partial replacement, but still feasible.

Implant wear is another consideration. Partial replacements experience higher contact stress on the implant surface because the load is concentrated in one area. This can lead to wear over time, especially in younger, more active patients. Your surgeon will discuss this risk during your consultation.

Activity and lifestyle after partial knee replacement

One advantage of a partial replacement is that it preserves more of your natural knee anatomy, which some surgeons believe allows for more natural movement and better long-term function. Many people report that their knee feels more "normal" after a partial replacement than after a total replacement.

Most surgeons recommend low-impact activities: walking, swimming, cycling, golf, and hiking on flat terrain. High-impact activities like running, jumping, or competitive sports are generally discouraged because they accelerate implant wear and increase the risk of complications.

Your surgeon will give you specific guidelines based on your age, activity level, and the type of implant used. Some newer implants are designed to tolerate higher activity, but this is something to discuss before surgery.

Cost and insurance coverage

A partial knee replacement typically costs less than a total replacement because less material is used and the surgery is shorter. However, the exact cost varies widely by location, hospital, surgeon, and your insurance plan. Hospital charges, surgeon fees, anesthesia, and implant costs all factor in.

Most insurance plans, including Medicare, cover partial knee replacement when it meets medical necessity criteria — meaning your surgeon documents that damage is isolated to one compartment and conservative treatment has failed. You will need to check your specific plan for deductibles, copays, and any prior authorization requirements.

If you are uninsured or underinsured, ask your surgeon's office about payment plans or hospital financial information programs. Some hospitals offer discounts for uninsured patients who pay upfront.

Frequently Asked Questions

Can I get a partial knee replacement if I am overweight?

Weight is a consideration because extra load on the implant can accelerate wear. Your surgeon will assess whether your weight, combined with your age and activity level, makes a partial replacement a good long-term choice. In some cases, losing weight before surgery improves outcomes. This is a conversation to have with your surgeon during your consultation.

What happens if arthritis develops in another compartment after my partial replacement?

Your surgeon can convert the partial replacement to a total replacement. This is a more involved surgery than the original partial replacement because the surgeon must work around the existing implant, but it is a standard procedure. The timing depends on your symptoms — you do not need revision unless pain or function declines.

How long does a partial knee replacement implant last?

Most implants last 15 to 20 years. Some last longer, especially in less active patients. Younger, more active patients may experience wear sooner. Your surgeon can discuss expected lifespan based on your age and activity level.

Is physical therapy required after a partial knee replacement?

Yes. Physical therapy is essential to regain motion, strength, and function. Most people begin within a few days of surgery and continue for 6 to 12 weeks. Skipping or cutting short therapy increases the risk of stiffness and poor outcomes.

Can I return to running or sports after a partial knee replacement?

Most surgeons advise against high-impact activities like running or competitive sports because they accelerate implant wear. Low-impact activities like walking, swimming, and cycling are generally safe. Your surgeon will give you specific guidance based on your implant type and overall health.