Knock Knees (Genu Valgum)

Description

Knock knees (genu valgum) is the opposite of bow legs: when a child stands with the knees together, the ankles stay apart, and the legs angle inward at the knee. It is very common in young children and, like bow legs, is usually a normal phase of development.

How it happens (mechanism)

Knock knees are part of the same normal alignment arc that produces bow legs. After the bow-legged infant phase straightens out around age 2, children naturally swing the other way into a knock-kneed phase, most pronounced around age 3 to 4. The legs then gradually straighten to adult alignment by about age 7. This back-and-forth is simply the normal pendulum of growing leg alignment, called physiologic genu valgum.

Less often, knock knees are caused by something other than normal development. Pathologic causes include rickets or other metabolic bone disease, a previous injury to a growth plate near the knee (which can make one side grow unevenly), skeletal dysplasias, and, in older or heavier children, persistent knock knees with knee pain. The clues that point away from a normal phase are asymmetry, persistence past about age 7, pain, or short stature.

What matters

As with bow legs, the goal is to separate the normal developmental phase — symmetric, roughly ages 2 to 6, and improving — from pathologic knock knees that are asymmetric, persistent past about age 7, painful, or associated with short stature. Normal knock knees need only reassurance and time; braces, inserts, and special shoes do not help. When knock knees are genuinely persistent or severe near the end of growth, a small guided-growth procedure can gently steer the legs straight — but that is the exception, not the rule.

How it is diagnosed

Diagnosis is clinical, often tracking the distance between the ankles when the knees are together over time. A standing alignment X-ray is obtained if the knock knees are asymmetric, persist past about age 7, are painful, or come with short stature, to look for an underlying cause.

Treatment

Physiologic knock knees resolve on their own and need only observation. For knock knees that persist or are severe near skeletal maturity, guided growth — a small implant placed at the growth plate that gently redirects growth toward straight — is an effective, minor procedure; an osteotomy is reserved for older or more severe cases. Any underlying cause, such as rickets, is treated directly.

Recovery and long-term outlook

The great majority of children with knock knees have the normal developmental form and end up with straight legs by around age 7, with no treatment. When treatment is needed for persistent valgus, guided growth near the end of growth generally corrects alignment reliably.

When to call the doctor

Contact the office if the knock knees are clearly worse on one side, are getting worse rather than better, persist well past age 7, are painful, or come with short stature.

Learn more

POSNA OrthoKids — Bowed Legs & Knock Knees: orthokids.org

This information is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. For specific concerns about your child, consult a board-certified, fellowship-trained pediatric orthopaedic surgeon.