Colgan Osteopath in Kettering Northamptonshire
The patella, or kneecap, can be a source of knee pain when it fails to function properly. Alignment or overuse problems of the patella can lead to wear and tear of the cartilage behind the patella. Chondromalacia patella is a common knee problem that affects the patella and the groove it slides in over the femur (thigh bone). This action takes place at the patellofemoral joint.
Chondromalacia is the term used to describe a patellofemoral joint that has been structurally damaged, while the term patellofemoral pain syndrome (PFPS) refers to the earlier stages of the condition. Symptoms are more likely to be reversible with PFPS.
The patella (kneecap) is the moveable bone on the front of the knee. This unique bone is wrapped inside a tendon that connects the large muscles on the front of the thigh, the quadriceps muscles, to the lower leg bone. The large quadriceps tendon together with the patella is called the quadriceps mechanism. Though we think of it as a single device, the quadriceps mechanism has two separate tendons, the quadriceps tendon on top of the patella and the patellar tendon below the patella.Tightening up the quadriceps muscles places a pull on the tendons of the quadriceps mechanism. This action causes the knee to straighten. The patella acts like a fulcrum to increase the force of the quadriceps muscles.
The underside of the patella is covered with articular cartilage, the smooth, slippery covering found on joint surfaces. This covering helps the patella glide (or track) in a special groove made by the thighbone, or femur. This groove is called the femoral groove.
Two muscles of the thigh attach to the patella and help control its position in the femoral groove as the leg straightens. These muscles are the vastus medialis obliquus (VMO) and the vastus lateralis (VL). The vastus medialis obliquus (VMO) runs along the inside of the thigh, and the vastus lateralis (VL) lies along the outside of the thigh. If the timing between these two muscles is off, the patella may be pulled off track.
Problems commonly develop when the patella suffers wear and tear. The underlying cartilage begins to degenerate, a condition most common in young athletes. Soccer players, snowboarders, cyclists, rowers, tennis players, ballet dancers, and runners are affected most often. But anyone whose knees are under great stress is at increased risk of developing chondromalacia patella.
Wear and tear can develop for several reasons. Acute injury to the patella or chronic friction between the patella and the femur can result in the start of patellofemoral pain syndrome. Degeneration leading to chondromalacia may also develop as part of the aging process, like putting a lot of miles on a car.
The main cause of knee pain associated with patellofemoral pain syndrome is a problem in the way the patella tracks within the femoral groove as the knee moves. Physical and biomechanical changes alter the stress and load on the patellofemoral joint.
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 the articular cartilage leading to chondromalacia patella.
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 vastus medialis obliquus (the muscle on the inside of the front of the thigh) and the vastus lateralis ( the muscle that runs down the outside part of the thigh) are two of these four muscles. 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 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. Doctors refer to this the “Q angle”. 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.
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.
The most common symptom is pain underneath or around the edges of the patella. The pain is made worse by any activities that load the patellofemoral joint, such as running, squatting, or going up and down stairs. Kneeling is often too painful to even try. Keeping the knee bent for long periods, as in sitting in a car or movie theater, may cause pain.
There may be 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 experience vague pain in the knee that isn’t centered in any one spot.
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.
Colgan Osteopath in Kettering Northamptonshire
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