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Chondromalacia patellae Alternative Names
CMP, Anterior knee pain
Definition
Runner's knee is a condition causing pain in the front of the knee often due to excess wear on the underside of the kneecap. It is also called chondromalacia patellae. Chondro- means cartilage, -malacia means softening or roughening, and patella means kneecap.
What is going on in the body?
When the knee is bent and straightened, the kneecap glides back and forth over the end of the femur, or thighbone. The underside of the kneecap is in contact with the femur. Like the rest of the knee joint, this surface is covered with cartilage. Cartilage is the glistening, smooth, white substance that is also found in animal joints. Too much stress between the kneecap and the femur can damage the cartilage, and the joint surface becomes softened and roughened. This wear causes joint irritation and pain.
Sometimes the joint swells because it produces extra fluid to improve lubrication. The contact pressure between the kneecap and femur varies according to activity. Deep knee bends exert a force equivalent to five times the body weight. Climbing stairs is equivalent to three times the body weight. Some people have the symptoms and physical findings of runner's knee without the underlying pathology in the cartilage.
What are the signs and symptoms of the condition?
Pain occurs in the front of the knee, around the kneecap. The pain can happen with activity, or even after prolonged sitting with the knees bent. Sometimes the knee will seem to give way, although this is not the true instability of a ligament tear. The knee may seem to lock when the rough surfaces of the kneecap and femur catch as they rub over each other. This is called pseudo-locking, which contrasts with the true locking seen with a meniscus tear or a loose body in the knee. If the joint is irritated enough, the lining of the joint cavity, called the synovium, may produce extra fluid. Synovial fluid, in small amounts, acts like oil to lubricate the joint and help the kneecap glide smoothly.
Sometimes a rubbing or clicking of the kneecap against the femur can be heard when the knee is bent and straightened. The edge of the kneecap may be tender. The knee may contain extra fluid, called an effusion, or water on the knee. In some cases, the kneecap tends to slide toward the outside of the knee. When the pain lasts a long time, the quadriceps, the thigh muscle that straightens the knee, can atrophy, or become smaller.
What are the causes and risks of the condition?
The problem is usually due to overuse when joggers run too long, too fast, or up too many hills. Conditions that cause the knee to be poorly aligned can contribute to extra stress on the patella. These include knock-knee, outward rotation of the lower leg, or inward rotation of the thighbone. A low position of the kneecap, called patella baja, or excessive pronation, which means a rolling in of the foot, can also put stress on the knee. Tight quadriceps muscles can increase the pressure on the kneecap.
What can be done to prevent the condition?
Stretching exercises are good for prevention of runner's knee, particularly those exercises designed for the quadriceps muscles. A moderate training program should avoid stress on the knee. Excessive distance, speed, and hills should be avoided. Orthotics, or arch supports, may help to reduce pronation of the foot.
How is the condition diagnosed?
The diagnosis is based on the symptoms and examination of the knee. X-rays are usually normal, although the x-rays may show a small amount of wear on the underside of the kneecap. Arthroscopy, a technique of visually inspecting the knee through a tubular instrument inserted into the joint, may be diagnostic.
What are the long-term effects of the condition?
Long-term effects are rare. If overuse continues and symptoms are ignored, arthritis is a possibility.
What are the treatments for the condition?
- Non-steroidal anti-inflammatory drugs (NSAIDs) may be used.
- Physiotherapy or proper instructions on particular exercises
What are the side effects of the treatments?
NSAIDs may have adverse effects on the stomach, kidneys, blood or liver.
What happens after treatment for the condition?
Proper training, preparatory stretching, and possibly the use of orthotics should be continued.
How is the condition monitored?
The effects of the running program on the knee are monitored.
Author:
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Contributors
Potential conflict of interest information for reviewers available on request |
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