What is chondromalacia patellae?

Chondromalacia patellae is a condition where there is damaged cartilage behind the patella (kneecap). It is like a softening or wear and tear of the cartilage.

The damage can range from slight to severe.

A note about terminology

Chondromalacia patellae overlaps with the knee condition known as patellofemoral pain syndrome. This is a term used by doctors to describe pain at the front of the knee, which can be from various causes, but which does not seem to be due to a severe problem such as serious arthritis or injury. See also the separate leaflet called Patellofemoral pain syndrome (Knee and kneecap pain).

The patella is the bone commonly known as the kneecap. It lies within the quadriceps tendon which is a large tendon at the bottom of the powerful thigh muscles (quadriceps) which then wraps around the patella and inserts into the top of the lower leg bone (tibia). The quadriceps muscles are used to straighten the leg.

The back of the patella is normally covered with smooth cartilage which helps the patella to glide over the lower part of the thighbone (femur) when the leg is straightened.

Chondromalacia patellae occurs most often in young adults and teenagers. It is more common in women. The reason why damage occurs to the cartilage is not clear. It is thought that the kneecap (patella) may rub against the lower part of the thighbone (femur) instead of gliding smoothly over it which may damage the patellar cartilage. Situations where this is more likely include the following:

• Overuse of the knee, such as in certain sports.

• Some people may have a slight problem in the alignment of the knee which may cause the patella to rub on, rather than glide over, the lower femur. This may be due to the way the knee has developed before birth or it may be due to an imbalance in the muscles around the knee - for example, if one side of the quadriceps muscles pulls harder than the other side, the patella may rub more on one side than the other.

• A combination of an alignment problem (as above) and overuse with sports, is likely to be the most common reason for developing chondromalacia patellae.

• Injury to the knee may contribute - perhaps repeated small injuries or stresses due to sports, or due to slack ligaments (hypermobile joints).

• In older people it may develop as part of the ageing process where there is wear and tear of cartilage in many joints.

• Pain around the knee. The pain is usually located at the front of the knee, around or behind the kneecap (patella). The pain is typically worse when going up or down stairs. It may be brought on by sitting (with the knees bent) for long periods.

• A grating or grinding feeling or noise when the knee moves (crepitus).

• Rarely, some fluid swelling (effusion) of the knee joint.

Usually, a provisional diagnosis of chondromalacia patellae is made from the symptoms plus an examination of the knee. This is a clinical diagnosis because the cartilage cannot be seen without further tests (see below). In this situation, where there is no proof of chondromalacia, some doctors call the pain "patellofemoral pain syndrome" or "anterior knee pain". The title does not matter as treatment will be the same at this point (see below).

Are any tests needed to diagnose chondromalacia patellae?

Usually no tests are needed as treatment can be started on the basis of a working diagnosis of chondromalacia.

Tests may be used in some situations, either to confirm the diagnosis or to rule out other causes. For example, if the diagnosis is not clear, or if symptoms do not improve after treatment, tests may be requested. These may include:

• Analyses de sang and/or a standard knee X-ray - these may help to rule out some types of arthritis or inflammation.

• Magnetic resonance imaging (MRI) scan) - shows details of the knee joint and can show up some cases of chondromalacia.

• Arthroscopy - a tiny flexible camera is inserted into the knee to see exactly what the cartilage looks like. This requires an anaesthetic and has a small risk of complications.

Evidence shows that conservative measures work better than surgical options. Exercises have been shown to be most effective; painkillers and taping have not been shown in studies to have long-term benefits. Stem cell transplant is a new potential treatment that is currently undergoing studies.

Traitement conservateur

• Avoid strenuous use of the knee - until the pain eases. Symptoms usually improve in time if the knee is not overused.

• Analgésiques - paracétamol may be advised to ease the pain. Anti-inflammatories such as ibuprofène may be helpful for pain in the short term but there is no evidence that they provide any long-term benefit.

• Physiothérapie - improving the strength of the muscles around the knee will ease the stress on the knee. Also, specific exercises may help to correct problems with alignment and muscle balance around the knee. See Further Reading below for examples of recommended exercises.

• Taping of the kneecap (patella) Adhesive tape is applied over the patella, to alter the alignment or the way the patella moves. Some people find this helpful. Some physiotherapists can offer patellar taping treatment.

Surgery for chondromalacia patellae

Surgery is not usually necessary but it may be advised if the above treatments have not helped. Arthroscopic surgery is the usual operation. A tiny flexible camera is inserted into the knee. The surgeon sees the inside of the knee joint and the cartilage, and may then operate through the camera tube, using very fine instruments. Possible surgical treatments are as follows:

• Tight ligaments on the side of the patella may be cut to allow the patella to align better and move more smoothly.

• Smoothing or shaving the cartilage behind the patella.

• Very rarely, if all other options do not help, the patella can be removed (the knee can still function without it).

The outlook (prognosis) is good. Most people get better with simple treatments such as physiotherapy. Chondromalacia does not seem to be linked to arthritis later in life.