Total Knee Replacement

Your knee

The knee joint connects the femur (thigh bone) and the tibia (shin bone). The knee can be thought of as a simple hinge-type joint permitting you to extend (straighten) and flex (bend) your knee. The actual movements of the knee are more complex and include rolling, pivoting, and small rotations on either side.

Similar to other joints, smooth articular cartilage covers the ends of these bones; uniquely in the knee, cartilaginous disks called menisci (singular: meniscus) further cushion and protect the knee. The combination of the articular cartilage and the menisci permits the knee bones to glide smoothly and effortlessly through motions of standing, sitting, jumping, running and taking stairs. Taking stairs and running for example, can exert 5-7 times your body weight on the knee joint.

The knee also has the patella bone (knee cap). The undersurface of the patella is covered with smooth articular cartilage, permitting it to easily slide up and down in a furrow on the femur and protects the inner ligaments of the knee.

The femur bone ends in two distinct half-doughnut shaped ridges or "condyles:" the medial (inside) condyle and the lateral (outside) condyle. In some patients, surgery may be performed on only one of the condyles or components, in what is referred to as partial or unicompartmental knee surgery.

Knee pain and arthritis

As in other joints, arthritis of the knee is caused by wear-and-tear of the cartilage at the end of the bones – in this case the ends of the femur and tibia, and underneath the kneecap. As the cartilage wears away, the bone ends rub against each other causing the grinding, accompanied by pain and swelling. As the arthritis progresses, there may be swelling around the knee, tenderness, stiffness and pain with the inability to straighten the knee. In severe cases, the knee may appear deformed with knock-knee or bow-legged deformities.

Arthritis is the most common cause of the breakdown of knee cartilage.

Osteoarthritis: also referred to as “wear and tear” arthritis; osteoarthritis affects the cartilage that cushions the ends of the knee bones. As this cartilage wears away, the ends of the bones rub together (bone-on-bone) causing a grinding feeling, knee pain and resulting stiffness.

Rheumatoid Arthritis: a systemic disease, which affects multiple joints in the body. The synovial membrane, which lines the entire joint cavity becomes irritated and produces too much fluid. The resulting healing response damages the cartilage, leading to pain and stiffness. Rheumatoid arthritis starts in much younger patients.

How is knee pain treated?

Non-surgical treatment options

In most cases, non-surgical treatments are exhausted before operative measures are considered, including:

• Physical therapy
• Weight loss
• Modifying your activities
• Using assistive devices, such as a cane
• Anti-inflammatory medicines

Physical therapy and exercise can help keep your joints flexible, strengthens the muscles around the joints, reduces pain and keeps your bone and cartilage tissue strong and healthy. If you start an exercise regimen, take a balanced approach and include aerobic activities such as walking, swimming and cycling in addition to stretching/flexibility exercises and strengthening exercises. You want to avoid exercises that place excessive stress on the joints like high-impact workouts or competitive sports activities.

Losing weight can have a surprising effect on reducing arthritic pain. With each step, you exert 4-7 times your body weight on your knee joints. So when you lose even a small amount of weight, your symptoms improve dramatically and you may be able to perform more activities and potentially put off surgery for six months or longer.

Activity modifications include reducing high-impact and repetitive activities that place increased stresses on the knee joint. Guided yoga or pilates can also help reduce pain and improve mobility.

The use of a cane, usually in the hand opposite the affected knee, can reduce the stress across the knee joint. Anti-inflammatory medicines, such as ibuprofen and naproxen, can reduce the inflammation around the knee joint that is caused by the arthritis and provide significant pain relief.

If all non-operative treatments have been attempted and fail to reduce pain, then surgery to replace the knee joint is an option your doctor may discuss with you.

Knee surgery

Total knee replacement (TKR) is performed in patients with severe loss of knee cartilage due to injury or inflammation, wear and tear due to various types of arthritis or other aging-related changes in the knee. TKR is also known as knee arthroplasty, with the prefix arthro- referring to joints and the suffix -plasty referring to surgery.

In TKR, the worn cartilage is surgically removed and replaced with an implant that might be metal, plastic, or a combination of the two.

Joint replacement surgery was developed in the early 1960’s, with significant advancements made by Mass General physicians and researchers. Mass General remains at the forefront of joint replacement innovation, with surgeons and researchers developing and implementing the latest minimally invasive techniques and surgical technology, including robot-assisted replacement surgery for hip and knee.

Knee replacement surgery has advanced to the point where many otherwise-healthy patients can have the procedure done on an outpatient basis as day surgery. This means, qualified patients who undergo knee replacement surgery are discharged the day of their procedure to rest and begin recovery in the comfort of their own home.

Total knee replacement is not the only type of joint surgery your surgeon may discuss with you. For patients with trauma or severe arthritis in both knee joints, your doctor may recommend a double knee replacement, also known as a bilateral knee replacement.

Partial knee replacement (unicompartmental knee replacement)

In some cases, arthritis of the knee is confined to a single compartment (or condyle) of the femur. If your doctor determines it appropriate for your individual case, they may only replace the damaged parts of the joint, and the healthy compartment of the knee is left alone. This is referred to as a partial knee replacement, and is only an option for certain patients.

Because a partial knee replacement is done through a smaller incision, the surgery is quicker, the hospital stay is shorter, and patients can rehabilitate and return to normal activities faster.

Are knee replacements permanent?

Total knee replacement implants have a normal life span of 10-20 years. With time, the artificial components wear out and may need to be replaced through a second knee surgery, also known as a total knee revision. Implants may also need to be replaced due to infection or pain in or around the implant, or other factors as determined by your doctor.