Partial Knee Replacement (Unicompartmental)

The goal of knee replacement surgery is to decrease pain and restore function. Although total knee replacement (also called "arthroplasty") is an excellent option for patients with osteoarthritis of the knee, other surgical options exist. Patients with osteoarthritis that is limited to just one part of the knee may be candidates for unicompartmental knee replacement (also called a "partial" knee replacement).

Description

A normal knee joint: Some structures have been removed to better show the smooth healthy cartilage lining the joint. The medial, lateral, and patellofemoral compartments are shown with red arrows.

Unicompartmental knee replacement is an option for a small percentage of patients with osteoarthritis of the knee. Your orthopedic doctor may recommend partial knee replacement if your arthritis is confined to a single part (compartment) of your knee.

Your knee is divided into three major compartments: The medial compartment (the inside part of the knee), the lateral compartment (the outside part), and the patellofemoral compartment (the front of the knee between the kneecap and thighbone).

In a unicompartmental knee replacement, only the damaged compartment is replaced with metal and plastic. The healthy cartilage and bone in the rest of the knee is left alone.

Advantages of Partial Knee Replacement
Multiple studies have shown that modern unicompartmental knee replacement performs very well in the vast majority of patients who are appropriate candidates.

The advantages of partial knee replacement over total knee replacement include:

• Quicker recovery
• Less pain after surgery
• Less blood loss
• Feels more "natural" than a total knee replacement.
• Possible increased bending

The disadvantages of partial knee replacement compared with total knee replacement include slightly less predictable pain relief, and the potential need for more knee surgery. For example, a total knee replacement may be necessary in the future if arthritis develops in the parts of the knee that have not been replaced.

In a partial knee replacement, only the damaged compartment is replaced with an artificial device.

Candidates for Surgery
Your orthopedic doctor may recommend surgery if you have more advanced osteoarthritis and have exhausted the nonsurgical treatment options. Surgery should only be considered if your knee is significantly affecting the quality of your life and interfering with your normal activities.

In order to be a candidate for unicompartmental knee replacement, your osteoarthritis must be limited to one compartment of your knee. Good candidates for the procedure are typically older people with less active lifestyles. Only about 7 out of 100 patients with arthritic knees are good candidates for unicompartmental knee replacement.

Knee osteoarthritis. (Left) This knee is not a good candidate for partial knee replacement because the arthritis affects both the medial (inner) and lateral (outer) compartments. (Right) In this knee, the arthritis is limited to the lateral compartment. This patient may be a good candidate for a unicompartmental knee replacement.

Good candidate for partial knee replacement. (Left) In this x-ray, the lateral compartment has a normal joint space, and the medial compartment has severe arthritis with "bone-on-bone" degeneration. (Right) The same knee after partial knee replacement.

Not a candidate for partial knee replacement. (Left) This x-ray shows severe arthritis in both the medial and lateral compartments. This patient is a good candidate for total knee replacement, as shown in the x-ray on the right.

Anesthesia
You will be admitted to the hospital on the day of your surgery. After admission, you will be evaluated by a member of the anesthesia team. The most common types of anesthesia are general anesthesia, in which you are asleep throughout the procedure, and spinal or epidural anesthesia, in which you are awake but your legs are anesthetized. An injection of numbing medication (nerve block) will also be administered during anesthesia that will significantly alleviate any pain after surgery. The anesthesia team will determine which type of anesthesia will be best for you with your input.

Surgical Procedure
A partial knee replacement operation typically lasts between 1 and 2 hours. Los Angeles orthopedic surgeon Dr. Samimi will make an incision at the front of your knee. He will then explore the three compartments of your knee to verify that the cartilage damage is, in fact, limited to one compartment and that your ligaments are intact. If Dr. Samimi feels that your knee is unsuitable for a partial knee replacement, he will instead perform a total knee replacement. He will discuss this contingency plan with you before your operation to make sure that you agree with this strategy.

If your knee is suitable for a partial knee replacement, he will use special saws to remove the cartilage from the damaged compartment of your knee and will cap the ends of the femur and tibia with metal coverings. The metal components are generally held to the bone with cement. A plastic insert is placed between the two metal components to allow for a smooth gliding surface.

After the surgery you will be taken to the recovery room, where you will be closely monitored by nurses as you recover from the anesthesia. You will then be taken to your hospital room.

Recovery
Because a partial knee replacement is done through a smaller, less invasive incision, hospitalization is shorter, and rehabilitation and return to normal activities is faster. Patients usually experience less postoperative pain, less swelling, and have easier rehabilitation than patients undergoing total knee replacement. In most cases, patients go home 1 to 3 days after the operation.

You will begin putting weight on your knee immediately after surgery. You may need a walker, cane, or crutches for the first several days or weeks until you become comfortable enough to walk without assistance.

A physical therapist will give you exercises to help maintain your range of motion and restore your strength. You will continue to see Dr. Samimi for follow-up visits in his clinic at regular intervals.

Complications
The complication rate following total knee replacement is low. Serious complications, such as a knee joint infection, occur in fewer than 2% of patients. Major medical complications such as heart attack or stroke occur even less frequently. Chronic illnesses may increase the potential for complications. Although uncommon, when these complications occur, they can prolong or limit full recovery.

Blood clots in the leg veins are the most common complication of knee replacement surgery. Your orthopaedic surgeon will outline a prevention program, which may include periodic elevation of your legs, lower leg exercises to increase circulation, support stockings, and medication to thin your blood.

Although implant designs and materials as well as surgical techniques have been optimized, wear of the bearing surfaces or loosening of the components may occur. Additionally, although an average of 115° of motion is generally anticipated after surgery, scarring of the knee can occasionally occur, and motion may be more limited, particularly in patients with limited motion before surgery.

Finally, although rare, injury to the nerves or blood vessels around the knee can occur during surgery.

Discuss your concerns thoroughly with your orthopedic surgeon prior to surgery.

Wound Care
You will have stitches or staples running along your wound or a suture beneath your skin on the front of your knee. The stitches or staples will be removed several weeks after surgery. A suture beneath your skin will not require removal.

Avoid soaking the wound in water until the wound has thoroughly sealed and dried. The wound may be bandaged to prevent irritation from clothing or support stockings.

Diet
Some loss of appetite is common for several weeks after surgery. A balanced diet, often with an iron supplement, is important to promote proper tissue healing and to restore muscle strength.

Activity
Exercise is a critical component of home care, particularly during the first few weeks after surgery. You should be able to resume most normal activities of daily living within 3 to 6 weeks following surgery. Some pain with activity and at night is common for several weeks after surgery. Your activity program should include:

• A graduated walking program to slowly increase your mobility, initially in your home and later outside
• Resuming other normal household activities, such as sitting and standing and climbing stairs
• Specific knee replacement exercises several times a day to restore movement and strengthen your knee. You probably will be able to perform the exercises without help, but you may have a physical therapist help you at home or in a therapy center the first few weeks after surgery.
• Driving usually begins when your knee bends sufficiently so you can enter and sit comfortably in your car and when your muscle control provides adequate reaction time for braking and acceleration. Most individuals resume driving approximately 4 weeks after surgery.

How Your New Knee Is Different
You may feel some numbness in the skin around your incision. You also may feel some stiffness, particularly with excessive bending activities. Improvement of knee motion is a goal of knee replacement, but restoration of full motion is uncommon. The motion of your knee replacement after surgery is predicted by the motion of your knee prior to surgery. Most patients can expect to be able to almost fully straighten the replaced knee and to bend the knee sufficiently to climb stairs and get in and out of a car. Kneeling is usually uncomfortable, but it is not harmful. Occasionally, you may feel some soft clicking of the metal and plastic with knee bending or walking. These differences often diminish with time and most patients find them to be tolerable when compared with the pain and limited function they experienced prior to surgery.

Your new knee may activate metal detectors required for security in airports and some buildings. Tell the security agent about your knee replacement if the alarm is activated.

After surgery
Participate in regular light exercise programs to maintain proper strength and mobility of your new knee.

Take special precautions to avoid falls and injuries. Individuals who have undergone knee replacement surgery and experience a fracture may require more surgery.

Notify your dentist that you had a knee replacement. You should be given antibiotics before all dental surgery for the rest of your life.

See your orthopedic surgeon periodically for a routine follow-up examination and x-rays (radiographs), usually once a year.