Definition

Knock knees are condition in which the knees touch, but the ankles do not touch. The legs turn inward.

Alternative Names

Genu valgum

Causes

Infants start out with bowlegs because of their folded position while in their mother's womb. The legs 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)

Exams and Tests

A health care provider will examine your child. Tests will be done if there are signs that knock knees are not a part of normal development.

Treatment

Knock knees are not treated in most cases.

If the problem continues after age 7, the child may use a night brace. This brace is attached to a shoe.

Surgery may be considered for knock knees that are severe and continue beyond late childhood.

Outlook (Prognosis)

Children normally outgrow knock knees without treatment, unless it is caused by a disease.

If surgery is needed, the results are most often good.

Possible Complications

Complications may include:

• 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

When to Contact a Medical Professional

Contact your provider if you think your child has knock knees.

Prevention

There is no known prevention for normal knock knees.

References

McClincy MP, Olgun ZD, Dede O. Orthopedics. In: Zitelli BJ, McIntire SC, Nowalk AJ, Garrison J, eds. Zitelli and Davis' Atlas of Pediatric Physical Diagnosis. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 22.

Pomeranz AJ, Sabnis S, Busey SL, Kliegman RM. Bowlegs and knock-knees. In: Pomeranz AJ, Sabnis S, Busey SL, Kliegman RM, eds. Pediatric Decision-Making Strategies. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 49.

Winell JJ, Baldwin KD, Wells L. Torsional and angular deformities of the limb. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 695.

Wimberly RL. Disorders of the leg. In: Herring JA, ed. Tachdjian’s Pediatric Orthopaedics. 6th ed. Philadelphia, PA: Elsevier; 2022:chap 18.