Unicompartmental Knee Replacement
Unicompartmental knee replacement is a minimally invasive surgery in which only the damaged compartment of the knee is replaced with an implant. It is also called a partial knee replacement. 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 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.
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, where as 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”. These factors can cause pain and restricted range of motion in the joint.
The exact cause is unknown, however there are several 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
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.
Your doctor will diagnose osteoarthritis based on the medical history, physical examination, and X-rays.
X-rays typically show a narrowing of joint space in the arthritic knee.
Your doctor may recommend 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. The three compartments of the knee will be visualized to ensure that the cartilage damage is limited to one compartment of the knee and that the ligaments are intact. If there is more damage than expected and your knee is unsuitable for a partial knee replacement, your surgeon may instead perform a total knee replacement surgery.
Your surgeon will remove the cartilage and bone ends in the damaged compartment. Metal implants are used to cover the bone ends and are fixed in place using bone cement. A plastic insert is placed between the metal components for a smooth gliding surface. Once the femoral and tibial components are fixed in proper place the knee is taken through a range of movements. The muscles and tendons are then repaired and the incision is closed.
You may walk with the help of a walker or cane for the first 1-2 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 but high impact activities such as jogging should be avoided.
Risks and Complications
Possible risks and complications associated with unicompartmental knee replacement include:
- Knee stiffness
- Blood clots (Deep vein thrombosis)
- Nerve and blood vessel damage
- Ligament injuries
- Patella (kneecap) dislocation
- Plastic liner wears out
- Loosening of the implant
The advantages of Unicompartmental Knee Replacement over Total Knee Replacement include:
- Smaller incision
- Less blood loss
- Quick recovery
- Less post-operative pain
- Better overall range of motion
- Feels more like a natural knee
Unicompartmental Knee Replacement - AAOS link