Unicompartmental arthroplasty (Partial Knee replacement)

What is unicompartmental knee arthroplasty?

The normal knee is a complex joint consisting of bones and soft tissue structures that are designed to move and tolerate forces of everyday activity. The forces of the knee are centralized in 3 areas or compartments. Each compartment takes in the stress of activity through cartilage. The three compartments are the medial or inside of the knee, the lateral, or outside of the knee and the knee cap and the groove that it rides back and forth in. Osteoarthritis may often develop in 1 of the 3 compartments of the knee, while the other two remain relatively healthy.

Patients that have osteoarthritis in 1 compartment may not need a total knee replacement to relieve pain and restore the function of the knee. The alternative option is the unicompartmental knee replacement, where only one side of the knee or one compartment needs replacing.

Using special, precision instruments the damaged surfaces are removed. The replacement surfaces are then fixed into place. The surface of the upper bone is replaced with a rounded metal component that comes very close to matching the curve of the natural bone. The surface of the lower bone is replaced with a flat metal component and a slab of ultra-high-molecular weight polyethylene plastic to serve as the cartilage, or the entire component may be plastic.

The goal is to save ALL of the ligaments in the knee. Ligaments are like small pieces of rope that hold the bones together.   The ligaments make the knee feel stable and secure during activity.  The knee has 4 ligaments that provide this function, one on each side and two that cross in the middle.

The UNI knee has the potential to function and feel more like a normal knee, especially during activity.

 

How can unicompartmental knee replacement help?

The goal of any form of knee replacement is to decrease pain, and allow routine activities to be performed with less difficulty.  This surgical procedure, the partial knee replacement, has generated significant interest because it entails a smaller incision and faster recovery than traditional total joint replacement surgery. More than 90 percent of individuals who undergo knee replacement surgery experience a dramatic reduction of knee pain and a significant improvement in the ability to perform common activities of daily living.

Following surgery, it will be important to avoid some types of activity, including jogging and high impact sports.  This is a long term recommendation.  With normal use and activity, every knee replacement develops some wear in its plastic cushion. Excessive activity or weight may accelerate this normal wear and cause the knee replacement to loosen and become painful. With appropriate activity modification, knee replacements can last for many years.

What sort of anaesthetic is used?

Most patients need to stay in hospital overnight.

Knee osteotomy can be performed under regional, or general anesthesia. Regional anesthesia numbs you below your waist, and general anesthesia puts you to sleep. The anesthetist will help you determine which is the most suitable for you.

What should I expect after the unicompartmental knee arthroplasty?

Most patients experience mild discomfort when they wake up after a partial knee replacement.

Wounds will be dressed with waterproof dressings under the outer bandage. The outer bandage may be removed 24hrs after surgery.  The smaller dressing is to remain intact for 7-10 days.

Walking is encouraged either the day of the operation of early the next morning.  Full weight bearing is allowed.  The knee should be exercised regularly for several weeks following surgery to strengthen the muscles of the leg and knee. A physiotherapist may help with an exercise program.

How Long will it take to recover?

Recovery after uni knee takes up to 18 months. This is the time it takes to regain muscle strength and see the full benefit of the surgery.  Patients are usually able to walk without crutches by 2 weeks and are mobilising comfortably by 6 weeks. Sedentary and office workers may return to work approximately 2 weeks following surgery. Driving a car is usually tolerated within four to six weeks after surgery.

Is physiotherapy required after unicompartmental knee arthroplasty ?

Physiotherapy is commenced immediately post operatively. A physiotherapist will supervise muscle contractions, walking and weight bearing.  This should continue daily following your surgery until the dressings are removed 7-10 days following surgery. Sedentary and office workers may return to work approximately 2 weeks following surgery.

Ongoing therapy aimed at strengthening the muscles around the knee and increasing knee motion is helpful for the first six months after surgery.  Often these exercises can be performed at home after guidance from a therapist.

What are the risks?

Unicompartmental knee arthroplasty is a very safe procedure. The most common side effect is temporary discomfort or slight bruising. Due to the skin incision patients may notice a numb patch on the outer aspect of their leg past the skin incision. This is of no functional significance and is unavoidable. The numb patch tends to shrink with the passage of time and does not affect the result of the surgery.

Following surgery there is a less than 1% chance of developing an infection. Most commonly these are superficial wound infections that resolve with a course of antibiotics. More serious infections may require further hospitalization and treatment. Injury to the blood vessels around the knee during surgery is a very rare complication (less than 1%). Other potential problems include post-operative stiffness, pain and wound problems and clots.