Partial Knee Replacement Replaces Only the Damaged Section of Your Knee

A partial knee replacement, also called unicompartmental knee replacement, removes and replaces only the worn cartilage and bone in one section of your knee joint. Your knee has three compartments — the inner (medial), outer (lateral), and kneecap (patellofemoral) — and a partial replacement addresses damage in just one of them, leaving the healthy compartments untouched.

This differs from a total knee replacement, which removes damaged surfaces from all three compartments and replaces them with artificial components. A partial replacement is smaller surgery with a shorter recovery, but it works only when damage is limited to one area and the other compartments are still healthy. Your surgeon will use imaging tests like X-rays or MRI to confirm that only one section is worn before recommending this approach.

The procedure typically takes 60 to 90 minutes. Your surgeon makes a smaller incision than in total replacement, removes the damaged bone and cartilage, and cements a metal and plastic implant in place. Because less bone is removed and fewer structures are cut, many people report less pain and faster return to daily activities compared to total replacement.

Key Takeaways

  • Partial knee replacement removes damaged cartilage and bone from only one of your knee's three compartments, leaving healthy sections in place.
  • This surgery is an option only if damage is confined to one area and your other compartments show little or no wear on imaging tests.
  • Recovery is typically faster than total knee replacement because the incision is smaller and less bone is removed.
  • Not all people with knee arthritis are candidates — your surgeon must confirm that your other compartments are healthy enough to support the implant.

When Surgeons Recommend Partial Replacement Instead of Total

Your surgeon will consider partial replacement if your imaging shows damage limited to one compartment and you meet certain other criteria. You are usually a better candidate if you are younger (often under 60, though age alone is not a barrier), have a lower body weight, do not have inflammatory arthritis like rheumatoid arthritis, and have good alignment in your knee. Inflammatory conditions tend to progress across all compartments, making total replacement more likely to be needed later.

Partial replacement also works better if you want to stay active and return to higher-impact activities sooner. Because less bone is removed, your knee retains more of its original structure and motion. Some people report that a partial replacement feels more natural than a total replacement, though this varies by individual.

If your other compartments already show moderate to severe wear, or if you have significant damage to the ligaments that stabilize your knee, your surgeon will likely recommend total replacement instead. The goal is to choose the approach that will last longest and function best for your specific damage pattern.

How Recovery Differs from Total Knee Replacement

Most people go home the same day or after one night in the hospital. Physical therapy usually begins within a few days, and many people walk without a cane or walker within two to four weeks. Return to light daily activities like walking, swimming, or stationary cycling often happens within six to eight weeks, compared to three to four months for total replacement.

Pain and swelling are typically less severe after partial replacement because the incision is smaller and less muscle is disturbed. You will still need to follow your surgeon's weight-bearing instructions and avoid high-impact activities during early healing, but the restrictions are usually less strict than after total replacement.

Full recovery — when swelling settles and strength returns to normal — usually takes three to six months. Some people feel improvement continues for up to a year as the implant settles and your body adapts to the new joint surface.

Risks and Limitations of Partial Replacement

The main risk is that arthritis will develop in one of the other compartments over time. Studies show this happens in roughly 10 to 15 percent of people within 10 years, though rates vary depending on your age, weight, and activity level. If arthritis develops in another compartment later, you may need a second surgery to convert to total replacement.

Partial replacement also carries a small risk that the implant will loosen or wear faster than expected, particularly if you are very active or overweight. Some surgeons are cautious about recommending it to people under 50 because the implant may not last through their lifetime, requiring revision surgery.

The surgery is also technically demanding — it requires precise alignment and sizing, and outcomes depend heavily on your surgeon's experience with the procedure. If the implant is placed incorrectly, it can wear unevenly or cause pain. Ask your surgeon how many partial replacements they perform each year; those who do 20 or more annually tend to have better results.

Implant Materials and How Long They Last

Partial knee implants use the same basic materials as total replacement implants: a metal component (usually cobalt-chromium or titanium) on the bone side and a plastic (polyethylene) bearing surface. The plastic can wear over time, especially if you are very active or have poor alignment.

Most partial knee implants last 15 to 20 years, though some last longer and some wear faster. Younger, lighter, and less active people tend to have implants that last longer. If your implant wears out, revision surgery is possible but more complex than the original procedure because some bone has already been removed.

Your surgeon will discuss the expected lifespan for your specific implant and your activity level. This conversation is important if you are young or very active, because you may face revision surgery during your lifetime.

Partial Replacement Versus Other Treatment Options

Before recommending surgery, your surgeon will usually discuss non-surgical options. Physical therapy, weight management, anti-inflammatory medications, and corticosteroid or hyaluronic acid injections can reduce pain and improve function in early to moderate arthritis. Many people manage single-compartment arthritis without surgery for years.

If non-surgical treatment stops working, partial replacement is one option. Total knee replacement is another, offering a longer-lasting implant but requiring more bone removal and longer recovery. Some surgeons prefer total replacement because it addresses all compartments at once and eliminates the risk of arthritis developing elsewhere later.

Your choice depends on your age, activity level, the extent of your damage, and your surgeon's recommendation. There is no single right answer — the best option is the one that matches your goals and your specific knee condition.

Questions to Ask Your Surgeon Before Deciding

Ask how many partial knee replacements your surgeon performs each year and what their complication rate is. Request imaging images so you can see exactly where your damage is. Ask what they expect your implant to last and what happens if it wears out before then.

Discuss your activity level and goals — if you want to run or play sports, ask whether partial replacement is realistic for you or whether total replacement might be more durable. Ask about the specific implant brand and design they use, and whether there are alternatives. Finally, ask what would make them recommend converting to total replacement later if arthritis develops in another compartment.

Frequently Asked Questions

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

Weight is a factor your surgeon will consider, but it is not an automatic disqualifier. Higher weight increases stress on the implant and can cause faster wear. Your surgeon will discuss whether your weight affects the durability outlook and may recommend weight loss before surgery to improve results.

Will I need a cane or walker after partial knee replacement?

Most people use crutches or a walker for the first one to two weeks, then transition to a cane for another week or two. Many people walk without any aid by four weeks. Your physical therapist will guide you on when it is safe to stop using assistive devices based on your strength and balance.

Can I play sports or run after partial knee replacement?

Low-impact activities like walking, swimming, and cycling are usually safe after full recovery. High-impact activities like running or jumping carry higher risk of implant wear and are generally not recommended, though some active people do return to these activities. Discuss your specific goals with your surgeon before deciding on surgery.

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

You can have a second surgery to convert to total knee replacement. This is more complex than the original partial replacement because bone has already been removed, but it is a standard procedure. This happens in roughly 10 to 15 percent of people within 10 years.

How long will I be off work after partial knee replacement?

If your job involves sitting or light desk work, you may return within two to four weeks. If your job requires standing, walking, or physical labor, recovery typically takes six to eight weeks or longer. Your surgeon will give you specific restrictions based on your job demands and your healing progress.