Introduction

Your knee is an important joint that supports the weight of your body and must function correctly for movement and walking. Your knee is made from bone, ligaments and cartilage. One type of cartilage covers the bones, and the other type cushions between the bones.

The knee is the most commonly injured joint in the body. Injuries to the knee are not always just to the bones, but also the ligaments, tendons or cartilage.  Your knees can be injured or affected by some kind of arthritis. The most common causes of knee injury include sports and accidents.

Symptoms of a knee injury or problem include pain, inability to put weight on your knee, stiffness, instability and swelling and even bruising if an injury happened suddenly.

When an injury or arthritis affects only one part of the knee, your doctor may talk to you about a partial knee replacement.  Your doctor may offer this procedure only after other treatments (injections, medication, and physical therapy) have not worked. This is a good option for patients who have arthritis in just one part of the knee, or who have a joint problem that is only in one section (compartment) of the knee.

During the surgery, your doctor will remove only the bone and tissue that needs to be taken out and replace it with metal and plastic parts. The rest of the healthy tissue and bone is left alone.

Many people who have a partial knee replacement do very well afterward and have a shorter healing time, lose less blood during surgery, and have less pain than  patients who have a total knee replacement.

Anatomy

Your knee is a hinge joint that joins the thighbone (femur) with the shinbone (tibia). There is a smaller bone that runs beside the shinbone (fibula) and the kneecap at the front of your knee. Surrounding these bones and connecting all around them are strap-like tissues called ligaments that keep the knee steady, connecting the bones to each other, and tendons that attach the muscles to the bones.

• The ACL (anterior cruciate ligament) keeps the shinbone from sliding forward on the thighbone.
• The PCL (posterior cruciate ligament) keeps the shinbone from sliding backward on the thighbone.
• Other ligaments on either side of the knee (medial and lateral collateral ligaments) keep the bones from shifting from side to side.

Where the shinbone and thighbone meets are two cushions made from cartilage (medial and lateral meniscus). Shaped like the letter “C” this cartilage provides shock absorption and keeps the two bones from rubbing together. There are also several sacs inside the joint that provide lubrication for movement. These are called bursae.

Causes

Osteoarthritis

Osteoarthritis is the most common type of arthritis affecting about 21 million Americans. It tends to develop as people grow older. Osteoarthritis can result from overuse of a joint during sports or work.

The most common reason you may need a partial knee replacement is arthritis (osteoarthritis). Arthritis causes swelling and damage around the padding in the knee (cartilage) , causing it to wear away. As the bones begin to rub against one another, abnormal bone growths, called spurs, can grow around the joint. The bone spurs add to pain and swelling, while disrupting movement.

Osteoarthritis usually happens slowly, and may take years to get bad enough for you to need a partial knee replacement.

Other problems

Some patients may need a partial knee replacement years after an old injury, like a car accident or another type of old injury to the cartilage or ligaments. Patients with rheumatoid arthritis are not candidates for a partial knee replacement because it is a disease of the whole joint and this procedure just treats one area.

Symptoms

Most patients who get arthritis in their knees are over age 50 but it can occur in patient who are younger, although this is rare. Just because you do not meet typical age requirements does not mean you should not have your knee pain checked. Other symptoms of arthritis usually happen in adults who are overweight, and some doctors think that there may be a genetic link as well. This could mean that if your mother, father or siblings have had a knee replacement, there may be a higher chance that you will need one.

The most common arthritis symptoms you may notice include:

• Pain
• Swelling
• Stiffness
• Feeling like your knees are going to “give out” or collapse
• Tenderness around the knee
• Symptoms may fluctuate with the weather
• You may experience good and bad days with knee pain

Diagnosis

To diagnose the cause of your knee problems, your doctor will take a history. Try to make a note of any injuries you have had to your knees and when. If you cannot remember, ask a family member, or take along a friend or loved one with you who can help you. Next, the doctor will examine your knee and watch you walk.

You will need an X-ray of your knee. This will show the doctor if the space between your thigh and shinbones has gotten smaller. (This is because the cartilage or padding is worn away and not taking up as much space as it used to). To make sure you do not have rheumatoid arthritis, your doctor may do blood tests, or test fluid from your joint if it is swollen.

Treatment

Non-surgical treatment

If you are considering a partial knee replacement, you have probably tried non-surgical treatments. If you have not, your doctor will want you to start with those. He or she may suggest losing weight, adjusting your exercise routine, supportive braces, medication or physical therapy. There are injections that can be placed into the knee that can bring relief for weeks or months, allowing you to put off the surgery.

Surgical treatment

Surgical treatment will involve replacing the worn cartilage with metal or plastic replacement parts. To do the surgery, your doctor will replace the area of arthritis with a metal cap and put in a plastic liner. This will let the metal and plastic move smoothly like your old knee should have; and without the arthritis and painful tissue in your knee, you will be able to move and enjoy activities again.

Your doctor will closely examine your X-rays to determine where your arthritis is most severe and decide if you are a good candidate for a partial replacement. If you have very advanced arthritis, you will not be a good candidate for a partial replacement and will need a total knee replacement. Your doctor will help you make the right decision.

Surgery

On the day of surgery, your doctor will give you specific instructions, and you may be admitted to the hospital. Many doctors are doing partial knee replacements as an outpatient procedure now. This means you can go to a surgical center or hospital’s same day surgery department for your procedure and go home the same day. Your doctor will decide if you need an overnight hospital stay or if you will be able to go home after your procedure.

Before your surgery, the doctor in charge of controlling your pain during surgery(anesthesiologist) will come in to see you. He or she will examine you and take a medical and anesthesia history. Some doctors will do a partial knee replacement while you are awake, but numb from the waist down. This is called spinal anesthesia or an epidural. Other physicians or patients choose to be asleep for the surgery (general anesthesia). If you decide you want to be asleep, that is okay.

Your doctor will also stop in to see you before surgery and sign your knee. This helps operating room staff know which knee to clean and prepare, and ensures the correct knee is operated on.

Once you are asleep, a partial knee replacement usually takes 1-2 hours. During the procedure, your doctor makes a cut down the front of your knee and will confirm that the arthritis is not in more than one area. If it is, he or she may do a total knee replacement instead. Do not worry though—this won’t be a surprise because your doctor will have talked about this with you before surgery, and you must give permission and sign a consent for the procedure, just in case.

If everything looks good for the partial knee replacement, your doctor will use a special saw to cut away the damaged bone and cartilage from your knee and will cap the bones that have been rubbing against each other with a thin pieces of smooth metal that are usually cemented into place. Your new plastic padding is then fitted between the metal caps and secured in place.

After surgery, you will spend about an hour in the recovery area and then either be moved to a hospital room or out to your same-day surgery room and prepare to go home.

Recovery

Because a partial knee replacement is done through a smaller incision and with less damage to other parts of the knee, you will recover faster than patients who have a total knee replacement. Most patients are able to put weight on their knee right after surgery but you may need a walker, cane or crutches to help you until you feel steady and strong enough to walk without it.

Your doctor may recommend that you begin physical therapy, or may give you some activities to do at home to help your knee movement and flexibility. You shouldn’t begin any exercise routines or vigorous activity until your doctor says it is okay. He or she will also want to see you for follow-up appointments at regular intervals and will tell you when you can start doing normal activities again.

Every situation will vary, but most patients experience a steady recovery and are able to drive or return to work in a few weeks. You will be advised to avoid high-impact activities (like running), and will have to adjust routines to accommodate your knee replacement and ensure that it works for many years to come.

Complications

Every surgical procedure has some type of risk, and your doctor will talk with you about these risks before surgery. Problems after partial knee replacement can include:

• Blood clots: Some patients can develop a blood clot in the veins deep in the leg. Blood thinners are used to prevent this.
• Infection: Any time you have surgery, there is a chance that the area of the surgery could get infected. Your doctor will start you on antibiotics before your surgery, typically given by IV right before your surgery begins.
• Continued pain or nerve damage. Although rare, sometimes nerves are stretched or damaged during your procedure. These nerves may never fully recover. There is also a chance that your pain may not go away completely. Of course, you will have pain for a period of time after your surgery, but long-term pain does not usually continue.