Partial Knee Replacement

Partial knee replacement, also known as unicompartmental knee arthroplasty, is a surgical procedure that replaces only the damaged part of your knee joint, rather than the entire joint. This surgery is an option for people with arthritis or other damage affecting just one area of the knee, aiming to relieve pain and improve function while preserving healthy bone and tissue.

What is Partial Knee Replacement?

Partial knee replacement is a surgical procedure that replaces only the diseased or damaged part of your knee joint with artificial components, called a prosthesis. Unlike a total knee replacement, which replaces all three compartments of the knee, this surgery targets only one affected area, typically the inner (medial) compartment. This approach preserves healthy bone, cartilage, and ligaments in the unaffected parts of the knee.

During a partial knee replacement, a surgeon removes damaged cartilage and a small amount of bone from one specific area of the knee. This is most often the inner part of the knee, but it can also be the outer part or the kneecap area. The removed tissue is then replaced with metal and plastic implants designed to mimic the natural movement of the knee. This procedure is also known as unicompartmental knee arthroplasty. It is a less invasive option than total knee replacement because it involves a smaller incision and less disruption to the surrounding healthy tissues. The goal is to reduce pain and restore mobility in the affected compartment while maintaining the natural feel and function of the rest of the knee joint. The knee joint is divided into three main sections, or compartments: the medial (inner) compartment, the lateral (outer) compartment, and the patellofemoral (front, under the kneecap) compartment. Partial knee replacement is suitable when damage is confined to just one of these areas, allowing the surgeon to address only the problematic section.

Why it's done

Partial knee replacement is performed to relieve pain and improve function in people whose knee arthritis or damage is limited to only one part of the knee. It is typically recommended for individuals with severe arthritis in a single compartment who have not found relief from non-surgical treatments like medication, physical therapy, or injections. The goal is to restore a more natural knee motion and reduce discomfort.

This surgery is primarily done for people with osteoarthritis, a common type of arthritis where the cartilage that cushions the ends of bones wears away, causing pain and stiffness. If this wear and tear is confined to just one compartment of the knee, a partial replacement can be an effective solution. It is often considered for those whose pain significantly interferes with daily activities. Another reason for partial knee replacement is osteonecrosis, a condition where a lack of blood supply causes bone tissue to die. If osteonecrosis affects only a limited area of the knee, a partial replacement can remove the damaged bone and replace it with an implant. This can prevent further collapse of the joint and alleviate pain. Candidates for partial knee replacement usually have strong knee ligaments, such as the anterior cruciate ligament (ACL), and good range of motion in the knee. The surgeon will assess the overall health of the knee to ensure that the other compartments are healthy enough to support the partial replacement. This procedure is generally not suitable for people with widespread arthritis or inflammatory arthritis like rheumatoid arthritis.

How to prepare

Preparing for a partial knee replacement involves several steps to ensure you are healthy enough for surgery and to plan for your recovery. You will typically undergo a thorough medical evaluation, including blood tests and imaging, to assess your overall health and the condition of your knee. Discussing all medications with your doctor and arranging for post-surgery support are also crucial preparation steps.

Before your surgery, your doctor will conduct a complete physical examination. This may include blood tests, an electrocardiogram (ECG) to check your heart, and X-rays or magnetic resonance imaging (MRI) of your knee. These tests help ensure you are healthy enough for surgery and provide the surgical team with detailed images of your knee joint. You will need to discuss all medications, supplements, and herbal remedies you are taking with your surgeon. You may be advised to stop certain medications, such as blood thinners, several days or weeks before surgery to reduce the risk of bleeding. It is important to follow these instructions carefully. Planning for your recovery is also a key part of preparation. This includes arranging for someone to help you at home for the first few days or weeks after surgery, as you will have limited mobility. You might also need to make adjustments to your home, such as removing tripping hazards or installing grab bars, to make it safer and more accessible during your recovery. Your doctor may also recommend pre-surgery physical therapy to strengthen your muscles.

What happens during

During a partial knee replacement, you will receive anesthesia to ensure you are comfortable and pain-free throughout the procedure. The surgeon makes a small incision, typically 3 to 5 inches long, over the knee. They then remove the damaged cartilage and bone from the affected compartment and precisely fit the artificial implants. The procedure usually takes about one to two hours to complete.

Once the anesthesia has taken effect, the surgeon makes an incision on the front of your knee. This incision is generally smaller than that used for a total knee replacement, which helps minimize tissue damage and may lead to a faster recovery. The surgeon carefully moves aside muscles and tendons to access the damaged part of the knee joint. Using specialized instruments, the surgeon removes the worn-out cartilage and a small amount of underlying bone from the specific compartment being replaced. The healthy cartilage and bone in the other parts of the knee are left untouched. This precision is crucial for maintaining the natural mechanics of your knee. Next, the surgeon implants the artificial components (prosthesis). These typically consist of a metal cap for the end of the thigh bone (femur) and a metal tray with a plastic insert for the top of the shin bone (tibia). These components are carefully sized and positioned to restore smooth, pain-free movement. The surgeon then checks the knee's range of motion and stability before closing the incision with stitches or staples.

Recovery & timeline

Recovery from partial knee replacement is generally faster than from a total knee replacement, with most people able to walk with assistance on the same day or the day after surgery. You will typically stay in the hospital for one to three days. Full recovery, including a return to most normal activities, usually takes about three to six months, with consistent physical therapy being a vital part of rehabilitation.

After surgery, you will begin physical therapy very quickly, often within hours of the procedure. A physical therapist will guide you through exercises designed to restore strength, flexibility, and range of motion in your knee. These exercises are crucial for a successful recovery and preventing stiffness. Most people can put weight on their knee and walk with the help of crutches or a walker shortly after surgery. You will gradually increase your activity level as your pain decreases and your strength improves. Pain management is an important part of the early recovery period, and your medical team will provide medication to help control discomfort. Within a few weeks, many people can walk without assistance and resume light daily activities. However, it's important to avoid high-impact activities for several months to allow the knee to heal completely. Adhering to your physical therapy program and following your surgeon's instructions are essential for achieving the best long-term outcome. Full recovery, including the ability to return to more strenuous activities, can take up to six months or longer, depending on individual progress.

Risks & side effects

While partial knee replacement is generally safe, like any surgery, it carries potential risks and side effects. Common risks include infection, blood clots, nerve damage, and persistent pain. Less common but serious complications can include loosening of the implant, fracture, or the need for further surgery. Your surgical team will discuss these risks with you before the procedure.

Infection is a risk with any surgery, and while rare, it can occur after partial knee replacement. If an infection develops, it may require antibiotics or, in some cases, additional surgery to treat. To minimize this risk, you will typically receive antibiotics before and after your procedure. Blood clots in the leg veins (deep vein thrombosis) are another potential complication. These clots can be serious if they travel to the lungs. Your doctor may prescribe blood-thinning medications, compression stockings, or recommend early movement to help prevent clots. Swelling and bruising around the knee are common side effects that usually resolve over time. Other potential risks include nerve or blood vessel damage, which can lead to numbness or weakness. Some people may experience persistent pain, stiffness, or instability in the knee after surgery. In some cases, the artificial components may wear out or loosen over time, potentially requiring a revision surgery to replace the implants. Your surgeon will explain all potential risks based on your individual health profile.

Success rate

Partial knee replacement generally has a high success rate, with many people experiencing significant pain relief and improved knee function. Studies show that about 90% of partial knee replacements are still functioning well 10 years after surgery. The long-term success depends on factors like patient selection, surgical technique, and adherence to rehabilitation.

For carefully selected patients, partial knee replacement can provide excellent outcomes. The procedure is often associated with a more natural-feeling knee compared to a total knee replacement, as more of the original joint is preserved. Many people report being able to return to activities they enjoyed before surgery, with less pain. According to the Mayo Clinic, about 90% of partial knee replacements are still successful 10 years after the initial surgery. This means that for about 9 out of 10 people (90%), the implant is still functioning well and providing relief a decade later. Some studies suggest that the success rate can be even higher, with 80% to 90% of implants lasting 15 to 20 years. However, it's important to understand that the implants can wear out over time or other parts of the knee may develop arthritis. If the partial knee replacement fails, or if arthritis develops in the other compartments of the knee, a total knee replacement may be necessary in the future. Your surgeon will discuss the expected lifespan of the implant and the factors that can influence its longevity.

Frequently asked questions

How long does a partial knee replacement last?

A partial knee replacement typically lasts for many years. According to the Mayo Clinic, about 90% of these implants are still functioning well 10 years after surgery. Some studies suggest they can last 15 to 20 years or even longer for many individuals, depending on factors like activity level and overall health.

Is partial knee replacement less painful than total knee replacement?

Many people report less post-operative pain and a faster recovery with partial knee replacement compared to total knee replacement. This is because the surgery is less invasive, involves a smaller incision, and preserves more of the natural bone and soft tissues of the knee.

Can I return to sports after a partial knee replacement?

Many people can return to low-impact sports and activities like walking, swimming, and cycling after a partial knee replacement. High-impact sports, such as running or jumping, are generally not recommended as they can put excessive stress on the implant and potentially shorten its lifespan. Always follow your surgeon's specific recommendations.

What is the typical hospital stay for partial knee replacement?

The typical hospital stay for a partial knee replacement is relatively short, usually one to three days. Some people may even be able to go home on the same day of surgery, depending on their recovery progress and individual circumstances.

Will I need physical therapy after partial knee replacement?

Yes, physical therapy is a crucial part of recovery after a partial knee replacement. It helps restore strength, flexibility, and range of motion in your knee. Your physical therapist will guide you through exercises starting soon after surgery and continuing for several weeks or months.

What are the alternatives to partial knee replacement?

Alternatives to partial knee replacement include non-surgical treatments like pain medications, anti-inflammatory drugs, physical therapy, corticosteroid injections, or hyaluronic acid injections. Other surgical options might include arthroscopy for debridement or, if arthritis is widespread, a total knee replacement.

Sources

• MedlinePlus — Partial Knee Replacement
• Mayo Clinic — Partial Knee Replacement
• Cochrane Library — Partial Knee Replacement