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Knock knees

Definition

Knock knees is a condition in which the knees touch, but the ankles do not touch. The legs angle inward.

Alternative Names

Genu valgum

Causes, incidence, and risk factors

Infants start out with bowlegs because of their folded position in the uterus. The infant's bowlegs begin to straighten once the child starts to walk (at about 12 to 18 months). By age 3, the child becomes knock-kneed. When the child stands, the knees touch but the ankles are apart.

By puberty, the legs straighten out and most children can stand with the knees and ankles touching (without forcing the position).

Knock knees can also develop as a result of a medical problem or disease, such as:

• Injury of the shinbone (only one leg will be knock-kneed)
• Osteomyelitis (bone infection)
• Overweight or obesity
• Rickets (a disease caused by a lack of vitamin D)

Symptoms

Signs and tests

If a doctor's examination and review of the child's medical history indicate a specific cause for the knock knees other than normal development, your health care provider will order the appropriate studies.

Treatment

Knock knees are usually not treated.

If the problem is still present after age 7, the child may use a night brace, which is attached to a shoe or orthopedic shoe.

Surgery may be considered for knock knees that persist beyond late childhood and in which the separation between the ankles is severe.

Support Groups

Expectations (prognosis)

Children normally outgrow knock knees without treatment, unless it is caused by a disease. For cases needing surgery, the procedure provides good cosmetic results.

Complications

• Difficulty walking (very rare)
• Self-esteem changes related to cosmetic appearance of knock knees
• If left untreated, knock knees can lead to early arthritis of the knee

Calling your health care provider

Call your health care provider to schedule an evaluation if you suspect your child has knock knees.

Prevention

There is no known prevention for normal knock knees.

References

Hosalkar HS, Gholve PA, Wells L. Torsional and angular deformities. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 674.

Sass P, Hassan G. Lower extremity abnormalities in children. Am Fam Physician. 2003;68:461-468.