UKA stands for unicompartmental knee arthroplasty, a surgical procedure that replaces only the damaged portion of a knee joint rather than the entire joint. It’s commonly called a partial knee replacement. Unlike a total knee replacement, which resurfaces all three compartments of the knee, UKA targets just the one compartment where arthritis has worn away the cartilage.
The Three Knee Compartments
Your knee joint is divided into three distinct compartments: the medial compartment (the inner side of the knee), the lateral compartment (the outer side), and the patellofemoral compartment (the front of the knee, where the kneecap meets the thighbone). When arthritis damages only one of these areas while the other two remain relatively healthy, a surgeon can replace just the affected compartment. Most UKA procedures address the medial compartment, since the inner knee bears the majority of your body weight and tends to wear out first.
Who Qualifies for UKA
The primary requirement is that your arthritis is confined to a single compartment. Surgeons typically look for bone-on-bone contact on X-rays in one area while the remaining compartments still have intact cartilage. Your anterior cruciate ligament (ACL) also needs to be functional, since an unstable knee won’t support a partial implant well.
Several conditions that were once thought to disqualify patients are no longer considered barriers. Being younger than 60, weighing over 180 pounds, performing heavy physical work, or having anterior knee pain do not rule out UKA. Even some wear on the patellofemoral joint, particularly on the medial side, doesn’t negatively affect implant survival or functional results.
Absolute disqualifiers include inflammatory arthritis (like rheumatoid arthritis), significant ligament instability, poor bone quality or osteoporosis, prior removal of the meniscus in the opposite compartment, severe knee stiffness, and active infection anywhere in the body.
How UKA Compares to Total Knee Replacement
The biggest practical advantage of UKA over total knee replacement is a faster recovery. Because the surgery involves a smaller incision and preserves more of the knee’s natural structure, including the cruciate ligaments and the healthy compartments, patients generally regain mobility sooner and report the knee feeling more natural afterward. The procedure is also increasingly performed in outpatient surgery centers rather than hospitals, and that trend has been growing steadily since 2020, allowing patients to go home the same day.
The tradeoff is that UKA carries a higher chance of needing a second surgery down the road compared to total knee replacement. If arthritis progresses into the other compartments over time, the partial implant may eventually need to be converted to a total replacement. However, long-term data shows strong durability: implant survival rates are roughly 97% at five years, 96% at ten years, and 93% at fifteen years.
What Recovery Looks Like
You can expect to stand and walk with a walker on the same day as surgery. Most people need one to two weeks of rest at home before returning to light daily activities. Physical therapy begins soon after the procedure and typically continues for several weeks, focusing on rebuilding strength and restoring range of motion. Because the surgery preserves the knee’s healthy tissue and ligaments, the rehabilitation process is less intensive than what follows a total knee replacement.
Robotic-Assisted UKA
A growing number of UKA procedures are performed with robotic assistance, where the surgeon uses a robotic arm to guide bone cuts with greater precision. The results are measurable: patients who undergo robotic-assisted UKA are significantly more likely to have their implant components placed within 2 degrees of the target position. That improved accuracy translates to real outcomes. A meta-analysis published in BMJ Open found that robotic-assisted UKA had a 58% lower rate of revision surgery compared to the conventional technique. Better alignment means the implant wears more evenly, which extends its lifespan and reduces the chance of early failure.