Total Knee Replacement
When your knee hurts, even walking can be difficult. Total knee replacement can relieve this pain and increase motion so you can return to your everyday tasks and the activities you enjoy.
What Is Knee Replacement?
Knee replacement means removing the damaged ends of bone in the knee joint and replacing them with artificial parts called prostheses. Based on your needs, the surgeon can replace the entire joint (total knee replacement) or a portion of the joint (partial knee replacement).
How Does the Knee Work?
A joint is an area in the body where the ends of bones meet. In the knee joint, 3 bones meet: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). Fig.1 Articular cartilage covers the ends of the femur and tibia and the underside of the patella. Fig.2 The cartilage cushions the joint and enables the bones to move smoothly against one another. Two menisci (men-IS-sky), which are crescent-shaped discs of another type of cartilage, lie on the inner and outer sides of the tibia. Fig.3 They absorb the weight and shock your body places on the knee and help stabilize the joint. The synovial membrane that lines the rest of the joint produces fluid to lubricate the knee. Ligaments connect the bones to each other and stabilize the joint. Fig.4 Tendons connect the surrounding muscles to the bones. Fig.5 The quadriceps (front of thigh) and hamstrings (back of thigh) muscles give the knee strength. Together, the bones and soft tissues enable you to bend and straighten your leg. Fig.6
What Causes Knee Pain and Stiffness?
Disease and injury can damage the articular cartilage, causing it to wear or tear away from the bone. The remaining bare areas of bone rub against each other, resulting in pain and stiffness. Arthritis is the most common cause of long-term, disabling knee pain. Another cause is avascular necrosis.
Osteoarthritis typically affects people who are more than 50 years old and have family members with this disease. It causes the articular cartilage to wear away slowly. Fig.7
Rheumatoid arthritis can affect people of any age. In this form of arthritis, your body’s immune system attacks the synovial membrane. It becomes inflamed (swollen) and produces too much synovial fluid, which causes the joint to swell. Fig.8 Over time, inflammation damages the articular cartilage.
Traumatic arthritis results from a knee injury that directly or indirectly damages the articular cartilage. Indirect damage can occur over time after you fracture (break) a knee bone or tear a knee ligament.
Avascular necrosis is another condition that causes joint pain and loss of motion. With this condition, you lose blood supply to the femur at the knee. Without a good blood supply, the bone develops tiny fractures and, over time, collapses. Fig.9
What Are the Types of Knee Replacement?
Your surgeon can choose total or unicompartmental knee replacement surgery to best treat your condition and help you return to the activities you enjoy.
Standard Total Knee Replacement
Total knee replacement involves replacing most or all surfaces in the joint. Using the standard approach, the surgeon makes a 6-inch to 12-inch incision to expose the entire joint. Fig.10 He or she removes the ends of the femur and tibia and the undersurface of the patella. Fig.11A / Fig.11B Next, the surgeon shapes the bones to fit the parts of the prosthetic joint. The parts can be made of metal, plastic, or ceramic. Fig.12 The surgeon can secure the parts with special cement or with the press-fit method, which relies on bone growing into the parts to hold them in place. After ensuring that the parts fit properly and that the knee joint functions normally, the surgeon inserts a drain to release excess fluid during recovery and closes the incision. A medical team member applies a sterile bandage to the knee.
Unicompartmental (Partial) Knee Replacement
Your knee comprises the lateral (outer), medial (inner), and patellofemoral (kneecap) compartments. The surgeon might perform a unicompartmental knee replacement if the bones in only 1 of these compartments need treatment. Fig.13 He or she uses a 3-inch to 4-inch incision to expose the appropriate compartment and replaces only the damaged portions of the bones.
With this smaller incision, the surgeon does not cut the quadriceps muscle, which is the main muscle that controls the knee, or the tendon that crosses the front of the knee. Rehabilitation can be faster; hospitalization, shorter; and return to activities, quicker. The procedure carries the same risks as those associated with total knee replacement.
Risks and Complications
Knee replacement surgery carries risks and complications:
- Blood clots
- Damage to nerves, blood vessels, and bones around the knee Fig.14
- Reaction to anesthesia
- Loosening of the artificial parts or joint dislocation