Elbow Issues

Patellofemoral Problems

Causes
Problems commonly develop when the patella suffers wear and tear. The underlying cartilage begins to degenerate, a condition sometimes referred to as chondromalacia patella. Wear and tear can develop for several reasons. Degeneration may develop as part of the aging process, like putting a lot of miles on a car. 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 in the way the patella tracks within the femoral groove as the knee moves. The quadriceps muscle helps control the patella so it stays within this groove. If part of the quadriceps is weak for any reason, a muscle imbalance can occur. When this happens, the pull of the quadriceps muscle may cause the patella to pull more to one side than the other. This in turn causes more pressure on the articular cartilage on one side than the other. In time, this pressure can damage thearticular cartilage.

Weakness of the muscles around the hip can also indirectly affect the patella and can lead to patellofemoral joint pain. Weakness of the muscles that pull the hip out and away from the other leg, the hip abductor muscles, can lead to imbalances to the alignment of the entire leg – including the knee joint and the muscle balance of the muscles around the knee. This causes abnormal tracking of the patella within the femoral groove and eventually pain around the patella. Many patients are confused when their Physical Therapist begins exercises to strengthen and balance the hip muscles, but there is a very good reason that the therapist is focusing on this area.

A similar problem can happen when the timing of the quadriceps muscles is off. There are four muscles that form the quadriceps muscle group. As mentioned earlier, the VMO is one of these four muscles. The VMO is the section of muscle on the inside of the front of the thigh. The VL runs down the outside part of the thigh. People with patellofemoral problems sometimes have problems in the timing between the VMO and the VL. The VL contracts first, before the VMO. This tends to pull the patella toward the outside of edge of the knee. The result is abnormal pressure on the articular surface of the patella.

Another type of imbalance may exist due to differences in how the bones of the knee are shaped. These differences, or anatomic variations, are something people are born with. 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 here than men. The patella normally 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. This leads to a similar problem as that described above. As the patella slides through the groove, it shifts to the outside. This places more pressure on one side than the other, leading to damage to the underlying articular cartilage.

Biomechanical issues in the foot can change the alignment and rotation of the tibia and alter the angle of pull of the patella tendon. This too can lead to tracking problems of the patella in the femoral groove or breakdown of the patella tendon itself.

Finally, anatomic variations in the bones of the knee can occur such that one side of the femoral groove is smaller than normal. This creates a situation where the groove is too shallow, usually on the outside part of the knee. People who have a shallow groove sometimes have their patella slip sideways out of the groove, causing a patellar dislocation. This is not only painful when it occurs, but it can damage the articular cartilage underneath the patella. If this occurs repeatedly, degeneration of the patellofemoral joint occurs fairly rapidly.

People who have a high-riding patella are also at risk of having their patella dislocate. In this condition, called patella alta, the patella sits high on the femur where the groove is very shallow. Here the sides of the femoral groove provide only a small barrier to keep the high-riding patella in place. A strong contraction of the quadriceps muscle can easily pull the patella over the edge and out of the groove, leading to a patellar dislocation. Patella alta is most common in girls, especially those who have generalized laxity (looseness) in their joints.

Symptoms
When people have patellofemoral problems, they sometimes report a sensation 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.

Others report having pain around the front part of the knee or along the edges of the kneecap. These symptoms may be due to problems with the way the patella lines up in the femoral groove. But symptoms of patellar pain can happen even when the patella appears to be lined up properly.

Patellofemoral problems exist when there is damage to the articular cartilage underneath the patella. This does not necessarily mean that the knee will be painful. Some people never have problems. Others experience vague pain in the knee that isn’t centered in any one spot. Sometimes pain is felt along the inside edge of the patella, though it may be felt anywhere around or behind the patella. Typically, people who have patellofemoral problems experience pain when walking down stairs or hills. Keeping the knee bent for long periods, as in sitting in a car or movie theater, may cause pain.

The knee may 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, you may feel popping or clicking as you bend your knee. This can happen when the uneven surface of the underside of the patella rubs against the femoral groove. The knee may swell with heavy use and become stiff and tight. This is usually because of fluid accumulating inside the knee joint, sometimes called water on the knee. This is not unique to problems of the patella but sometimes occurs when the knee becomes inflamed.