Unicompartmental knee replacement (partial or unicondylar knee replacement) is a minimally invasive surgery in which only the damaged compartment of the knee is replaced with an implant. The knee can be divided into three compartments: patellofemoral, the compartment in front of the knee between the knee cap and thigh bone, medial compartment, on the inside portion of the knee, and lateral compartment which is the area on the outside portion of the knee joint.
Traditionally, total knee replacement was commonly indicated for severe osteoarthritis of the knee. In a total knee replacement, all worn out or damaged surfaces of the knee joint are removed and replaced with new artificial parts. Partial knee replacement is a surgical option if your arthritis is confined to a single compartment of your knee.
Disease Overview
Arthritis is inflammation of a joint causing pain, swelling (inflammation), and stiffness.
Osteoarthritis is the most common form of knee arthritis in which the joint cartilage gradually wears away. It most often affects older people. In a normal joint, articular cartilage allows for smooth movement within the joint, whereas in an arthritic knee the cartilage itself becomes thinner or completely absent. In addition, the bones become thicker around the edges of the joint and may form bony “spurs”. All of these factors can cause pain and restricted range of motion in the joint.
Causes
The exact cause is unknown, however, there are a number of factors that are commonly associated with the onset of arthritis and may include:
- Injury or trauma to the joint
- Fractures of the knee joint
- Increased body weight
- Repetitive overuse
- Joint infection
- Inflammation of the joint
- Connective tissue disorders
Symptoms
Arthritis of the knees can cause knee pain, which may increase after activities such as walking, stair climbing, or kneeling.
The joint may become stiff and swollen, limiting the range of motion. Knee deformities such as knock-knees and bow-legs may also occur.
Diagnosis
Your doctor will diagnose osteoarthritis based on medical history, physical examination, and X-rays. X-rays typically show a narrowing of joint space in the arthritic knee.
What happens in the surgery?
Your surgeon will discuss surgery if non-surgical treatment options such as medications, injections, and physical therapy have failed to relieve the symptoms.
During the surgery, a small incision is made over the knee to expose the knee joint. Your surgeon will reshape the top of the shinbone (tibia) and place a new metal surface onto this. Then the damaged end of the femur or thigh bone is reshaped to accommodate a new metal surface (component). Once the femoral and tibial components are fixed in the proper place, a plastic implant (liner) is placed in between them to recreate the joint and allow the knee to move freely. The muscles and tendons are then repaired and the incision is closed.
What happens after the surgery?
You may walk with the help of a walker or cane for the first few weeks after surgery. A physical therapist will advise you on an exercise program to follow for 4 to 6 months to help maintain range of motion and restore your strength. You may perform exercises such as walking, swimming, and biking. It would be best to avoid high impact activities such as jogging.
Risks and Complications
Possible risks and complications associated with unicompartmental knee replacement include:
- Knee stiffness
- Infection
- Blood clots (Deep vein thrombosis)
- Nerve and blood vessel damage
- Ligament injuries
- Dislocation of the liner
- Plastic liner wears out
- Loosening of the implant
- Arthritis in the other areas of the knee
Advantages
The advantages of unicompartmental knee replacement over total knee replacement include:
- Smaller incision
- Less blood loss
- Quicker recovery
- Less post-operative pain
- Better overall range of motion
- Feels more like a natural knee
- Reduced risk of complications (infection, clots)
