The patella, or kneecap, is the moveable bone on the front of the knee. The patella is wrapped inside a tendon connecting the large muscles on the front of the thigh and the quadriceps muscles, to the lower leg bone. This tendon is called the quadriceps tendon above the patella and the patellar tendon below the patella.
The quadriceps mechanism, made up of the patella and tendon, allows you to straighten out the knee. The patella acts like a fulcrum to increase the force of the quadriceps muscle. The underside of the patella is covered with articular cartilage, the smooth, slippery covering found on joint surfaces. This covering helps the patella glide in a groove made by the thighbone, or femur called the patellofemoral grove. Together the patella and the groove in the femur are called the patellofemoral mechanism.
Problems commonly develop when the patella suffers wear and tear. The underlying cartilage begins to degenerate. Degeneration may develop as part of the aging process. The patellofemoral joint is usually affected as part of osteoarthritis of the knee.
One of the more common causes of knee pain is a problem with the way the patella moves through the patellofemoral groove. If part of this muscle is weak a muscle imbalance can occur. When this happens, the pull of the quadriceps muscle may cause the patella to shift to the outside. This, in turn, causes more pressure on one side of the articular cartilage than the other. In time, this pressure can damage the articular cartilage.
Another type of imbalance may exist due to differences in how the bones of the knee are shaped. Some people are born with a greater than normal angle where the femur and the tibia (shinbone) come together at the knee joint. Women tend to have a greater angle than men. The patella sits at the center of this angle within the femoral groove. When the quadriceps muscle contracts, the angle in the knee straightens, pushing the patella to the outside of the knee. In cases where this angle is increased, the patella tends to shift outward with greater pressure. As the patella slides through the femoral groove, this places more pressure on one side than the other, leading to damage to the underlying articular cartilage.
In some cases one side of the patellofemoral groove may be smaller than normal. This may cause the patella to actually slip out of the groove, causing a patellar dislocation. This is not only painful, but can cause degeneration of the patellofemoral joint if dislocation repeatedly happens.
If you have patellofemoral problems, you may feel like the patella is slipping. This is thought to be a reflex response to pain and not because there is any instability in the knee.
Sometimes you may have pain around the front part of the knee or along the edges of the kneecap. These symptoms may be related to the way the patella lines up in the femoral groove. Symptoms of patellar pain, however, can happen even when the patella appears to be lined up properly.
In other cases you may notice a dull pain in the knee that isn’t centered in any one spot. Typically, if you have patellofemoral problems you may experience pain when walking down stairs or hills. Keeping the knee bent for long periods, such as sitting in a car or movie theater, may also cause pain. The knee may also grind, or you may hear a crunching sound when you squat or go up and down stairs.
If there is a considerable amount of wear and tear, popping or clicking may be felt when the knee is bent. This happens when the uneven surfaces of the underside of the patella and the femoral groove rub against one another. The knee may swell with heavy use and become stiff and tight. This is usually due to fluid accumulating inside the knee joint, sometimes called “water on the knee.”
Diagnosis begins with a complete history of your knee problem followed by an examination of the knee and the patella. X-rays may be ordered on the initial visit to your doctor. An X-ray can help determine if the patella is properly aligned in the patellofemoral groove. The X-ray may show arthritis between the patella and thighbone, especially when the problems have been present for a considerable amount of time.
Diagnosing problems with the patella can be confusing, so other tests, such as magnetic resonance imaging (MRI), may be suggested. The MRI machine uses magnetic waves rather than X-rays to show the soft tissues of the body.
This machine creates pictures that look like slices of the knee. Usually, this test is done to look for injuries, such as tears in the menisci or ligaments of the knee. Recent advances in the quality of MRI scans have enabled doctors to see the articular cartilage on the scan and determine if it is damaged. This test does not require any needles or special dye and is painless.
In some cases, arthroscopy may be used. Arthroscopy is an operation that involves placing a tube with a small fiber-optic TV camera into the knee joint, allowing the orthopedic surgeon to look at the structures inside the joint directly. The arthroscope allows your doctor to see the condition of the articular cartilage on the back of your patella. The vast majority of patellofemoral problems are diagnosed without resorting to surgery, and arthroscopy is usually reserved to treat the problems identified by other means.
Treatment begins by decreasing the inflammation in the knee. Rest and anti-inflammatory medications, such as aspirin or ibuprofen, may be suggested by your physician, especially when the problem is due to overuse.
Physical therapy can help in the early stages by decreasing pain and inflammation. Your physical therapist may suggest the use of ice massage and ultrasound to limit pain and swelling. You may also be directed to use a brace or tape the patella to help reduce pain. As the pain and inflammation become controlled, your physical therapist can provide several exercise options to help correct problems with flexibility, strength, foot or knee alignment, and muscle balance in the knee.
If these measures fail to improve your condition, surgery may be suggested. Arthroscopy is sometimes useful in the treatment of patellofemoral problems of the knee. Looking directly at the articular cartilage surfaces of the patella and the patellofemoral groove is the most accurate way of determining how much wear and tear there is in these areas. Your physician can also watch as the patella moves through the groove, and may be able to decide whether or not the patella is moving normally.
If there are areas of articular cartilage damage behind the patella that are creating a rough surface, special tools can be used by the surgeon to smooth the surface and reduce your pain. This procedure is sometimes referred to as “shaving” the patella. In more advanced cases of patellar arthritis, doctors may operate to repair or restore the damaged cartilage.
The type of surgery needed for articular cartilage is based on the size, type, and location of the damage. Along with surgical treatment to fix the cartilage, other procedures may also be done to help align the patella so less pressure is placed on the healing cartilage.
If your patella problems appear to be caused by a misalignment problem, a procedure called a lateral release may be suggested. This procedure is done to allow the patella to shift back to a normal position and relieve pressure on the articular cartilage. In this operation, the tight ligaments on the outside (lateral side) of the patella are cut, or released, to allow the patella to slide more towards the center of the femoral groove. These ligaments eventually heal with scar tissue filling the gap created by surgery.
For problems of repeated patellar dislocations or severe patellar malalignment, the doctor may also need to realign the quadriceps mechanism. In addition to the lateral release, the tendons on the inside edge of the knee (the medial side) may have to be tightened.
If the malalignment is severe, the bony attachment of the patellar tendon may also have to be shifted to a new spot on the tibia bone. Doctors can change the way the tendon pulls the patella through the groove in the femur by surgically removing a section of bone where the patellar tendon attaches on the tibia. This section of bone is then reattached on the tibia closer to the other knee.
Usually, the bone is reattached onto the tibia using screws. This procedure shifts the patella to the inside the knee. Once the surgery heals, the patella should track better within the center of the patellar groove, spreading the pressure equally on the articular cartilage.
Many doctors will have their patients participate in formal physical therapy after knee surgery for patellofemoral problems. Patients undergoing a patellar shaving usually begin rehabilitation right away. More involved surgeries for patellar realignment or restorative procedures for the articular cartilage require a delay before going to therapy.
The first few physical therapy treatments are designed to help control the pain and swelling from the surgery. The physical therapist will choose exercises to help improve knee motion and to get the quadriceps muscles toned and active again. Muscle stimulation, using electrodes over the quadriceps muscle, may be needed at first to get the muscle moving again.
As the program evolves, more challenging exercises are chosen to safely advance the knee’s strength and function. The key is to get the soft tissues in balance through safe stretching and gradual strengthening.
The physical therapist’s goal is to help you keep your pain under control, ensure you place only a safe amount of weight on the healing knee, and improve your strength and range of motion. When you are well underway, regular visits to the therapist’s office will end. The therapist will continue to be a resource, but you will be in charge of doing your exercises as part of an ongoing home program.