UNICOMPARTMENTAL KNEE REPLACEMENT

UNICOMPARTMENTAL(PARTIAL) KNEE PROSTHESIS:

During knee replacement surgery, damaged bone and cartilage is resurfaced with metal and plastic components. In unicompartmental knee replacement (also called partial knee replacement) only a portion of the knee is resurfaced. This procedure is an alternative to total knee replacement for patients whose disease is limited to just one area of the knee.
In knee osteoarthritis, the cartilage protecting the bones of the knee slowly wears away. This can occur throughout the knee joint or just in a single area of the knee. The knee is divided into three major compartments:

• Medial compartment (the inside part of the knee)
• Lateral compartment (the outside part)
• Patellofemoral compartment (the front of the knee between the kneecap and thighbone)

Advanced osteoarthritis that is limited to a single compartment may be treated with a unicompartmental knee replacement. During this procedure, the damaged compartment is replaced with metal and plastic. The healthy cartilage and bone, as well as all of the ligaments are preserved.

Who can benefit from partial knee replacement?

A person whose wear on the joint is limited to a single region of the knee, who is not excessively fat, Patients who do not have severe deformity in the leg may benefit. at the knee Range of motion should be near full. In general, ligaments in the knee and around the knee they need to be solid. Common rheumatic disease such as rheumatoid arthritis, lupus Patients with rheumatoid arthritis should be considered for partial knee replacement, as calcification occurs in the entire joint. not suitable.

Advantages of Partial Knee Replacement

Multiple studies show that a majority of patients who are appropriate candidates for the procedure have good results with unicompartmental knee replacement. The advantages of partial knee replacement over total knee replacement include:

• Quicker recovery
• Less pain after surgery
• Less blood loss

Also, because the bone, cartilage, and ligaments in the healthy parts of the knee are kept, many patients report that a unicompartmental knee replacement feels more natural than a total knee replacement. A unicompartmental knee may also bend better.

Candidates for Surgery

If the osteoarthritis has advanced and nonsurgical treatment options are no longer relieving the symptoms, the doctor may recommend knee replacement surgery. In order to be a candidate for unicompartmental knee replacement, the arthritis must be limited to one compartment of the knee. In addition, if the patient has any of the following characteristics, he/she may not be eligible for the procedure:

• Inflammatory arthritis
• Significant knee stiffness
• Ligament damage

Orthopaedic Evaluation

To diagnose the osteoarthritis an orthopaedics doctor should check the patient’s knee physically and get the patient’s history. Of course that will not be enough and the patient should be checked by MRI and X ray to confirm the exact diagnose.

Surgical Procedure
The surgeon will make an incision at the front of the knee. He or she will then explore the three compartments of the knee to verify that the cartilage damage is, in fact, limited to one compartment and that the ligaments are intact.
If the surgeon feels that the knee is unsuitable for a partial knee replacement, he or she may instead perform a total knee replacement. This contingency plan will have been discussed with the patient before the operation to make sure that the patient agree with this strategy.

There are three basic steps in the procedure:

• Prepare the bone: The surgeon will use special saws to remove the cartilage from the damaged compartment of the knee.
• Position the metal implants: The removed cartilage and bone is replaced with metal coverings that recreate the surface of the joint.
• Insert a spacer: A plastic insert is placed between the two metal components to create a smooth gliding surface.

Complications

As with any surgical procedure, there are risks involved with partial knee replacement. The surgeon will discuss each of the risks with the patient and will take specific measures to help avoid potential complications.
Although rare, the most common risks include:
Blood clots: Blood clots in the leg veins are a common complication of knee replacement surgery. Blood clots can form in the deep veins of the legs or pelvis after surgery. To prevent blood clot the patient should do periodic elevation of the legs, lower leg exercises to increase circulation, support stockings, and blood thinners such as warfarin (Coumadin), low-molecular- weight heparin, and aspirin can help prevent this problem.
Infection: After surgery an infection may occur in the skin over the wound or deep in the wound. The patient will be given antibiotics before the start of the surgery and these will be continued for about 24 hours afterward to prevent infection.
Injury to nerves or vessels: Although it rarely happens, nerves or blood vessels may be injured or stretched during the procedure.

Recovery

Hospital discharge: Partial knee replacement patients usually experience less postoperative pain, less swelling, and have easier rehabilitation than patients undergoing total knee replacement.
Pain management: After surgery, the patient will feel some pain, but the surgeon and nurses will make every effort to help the patient feel as comfortable as possible. Many types of medicines are available to help control pain, including opioids, non- steroidal anti-inflammatory drugs (NSAIDs), and local anesthetics.
Weightbearing: The patient will begin putting weight on the knee immediately after surgery. The patient may need a walker, cane, or crutches for the first several days or weeks until the patient become comfortable enough to walk without assistance.
Rehabilitation exercise: A physical therapist will give the patient exercises to help maintain the range of motion and restore the strength.
The patient will most likely resume all of the regular activities of daily living between 3 to 6 weeks after surgery.

What is the lifespan of partial knee replacement?

Wear may occur in areas where partial knee replacement has not been applied over the years. If this wear is too great, the need for a full knee replacement may arise. The 20-year survival of new generation partial knee prostheses is similar to full prostheses and is over 90%. Partial dentures are preferred in suitable patients because they have better knee range of motion, provide higher activity and give a more normal knee feeling compared to full dentures.