Patellar Dislocation: A Common Injury in Teens

The kneecap (patella) rests in a grove at the end of the femur bone. When the leg is moved, the kneecap moves up and down in this groove. Certain circumstances may cause the kneecap to pop out of its groove (dislocate) and move to the outer part of the knee. This dislocation of the patella or kneecap causes sudden acute pain and rapid swelling. There is obvious deformity to the knee.

Common Causes:

The kneecap is the most commonly dislocated bone in the body. More women than men experience kneecap dislocations due to the wider shape of the female pelvis. This wider shape produces sharper angles causing a lateral pull on the kneecap. This type of non-contact kneecap dislocation can happen because the kneecap is unstable or 'loose' in the joint or the kneecap is misaligned by being tilted or shifted in its groove. Also obesity, being knock-kneed and having high-riding kneecaps can contribute to kneecap dislocation.

A kneecap dislocation can be caused by either a non-contact (atraumatic) type of injury or a traumatic injury. When there is a quick twist of the leg in a different direction when the foot is planted on the ground, it can cause the kneecap to slip out of socket. When this happens, generally a ligament is torn. If the ligament does not properly heal, reoccurring injuries happen.

A traumatic type dislocation of the kneecap is usually caused by a sudden direct blow to the patella during sports activity. This is a limb-threatening emergency as the entire lower leg becomes completely displaced and misaligned from the upper leg and artery and nerve injuries can result from the lack of blood flow to the lower leg. Immediate medical care is needed.

Greater risk for patella dislocation occurs in individuals who participate in activities that require running and jumping and is seen generally in young athletes between the ages of 14 and 20 years of age. A kneecap dislocation is rarely seen after the age of 30.

Kneecap dislocations are frequently seen in baseball, basketball, running, football weight lifting, soccer and volleyball. It is also seen in gymnastics, cheerleading and dancing. Sudden twisting of the kneecap occurs causing the kneecap to slip out of socket, generally tearing a ligament. When this ligament does not properly heal, reoccurring injuries happen. A common cause of kneecap dislocation is forceful straightening of the leg during serving the ball in tennis and volleyball and in pitching softball.

Treatment and Rehabilitation:

Sometimes the displaced kneecap will spontaneously pop back into anatomical alignment and the sufferer will feel a dull clunk and immediate reduction in pain. This is called spontaneous reduction. If the reduction not happen spontaneously, a doctor will need to reduce the dislocation right away. After any dislocated kneecap injury, further medical treatment is needed to ensure no arterial or nerve damage has occurred. If further damage is found, surgical repair is done immediately.

Even in the case of spontaneous reduction, X-rays need to be taken to look for fractures. If no fracture is found, the knee is usually splinted for 3-6 weeks so the soft tissue around the kneecap can heal. Strengthening exercises are then prescribed to keep the kneecap in place. In some cases, physical therapy sessions are prescribed. Usually, a return to normal activities happens in one to three months. Chronic conditions can sometimes cause the kneecap to be unstable and surgery is needed to tighten the tendons to keep the kneecap in place.

Doreen Bradley Satter, RN is a Registered Nurse who has been working in the Portland, Oregon area for the past 35 years.

Sources: Doreen K. Satter, RN

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orthopedics.about.com/cs/patelladisorders