Bow Legs (Genu Varum)

Description

Bow legs (genu varum) means that when a child stands with the feet and ankles together, the knees stay apart and the legs curve outward. It is extremely common in babies and toddlers, and in that age group it is usually a normal stage of development. The job of evaluation is to separate ordinary, normal bowing from the less common conditions that need treatment.

How it happens (mechanism)

Children’s leg alignment follows a predictable arc: babies are naturally bow-legged from their folded position in the womb, straighten to neutral by about age 2, swing slightly knock-kneed around ages 3 to 4, and settle into adult alignment by about age 7. Normal bowing of this kind is called physiologic genu varum; it begins improving around 18 months and corrects by ages 3 to 4.

Bowing becomes a concern when it does not follow that arc. The main causes are:

• Infantile Blount’s disease (tibia vara) — a true growth disturbance of the inner (medial) part of the growth plate at the top of the shinbone. Because that part of the plate grows too slowly, the bone keeps tilting into more bowing instead of straightening. It tends to appear in toddlers (about ages 2 to 5), is more common in early walkers and in children with higher body weight, and is often worse on one side. It is self-reinforcing — the more bowed the leg, the more load falls on the inner plate, slowing it further.
• Adolescent (late-onset) Blount’s disease — the same inner-plate overload appearing in older, often heavier children and teens, frequently with knee pain.
• Rickets — weak, soft growing bone from low vitamin D, calcium, or phosphorus (nutritional or genetic), which bows under normal loads.

What matters

The central task is telling normal bowing apart from Blount’s disease or rickets, because their paths diverge sharply. Normal bowing is symmetric, occurs under age 2, and is improving — it needs only reassurance, and importantly, no braces or special shoes. Blount’s and rickets are suggested by bowing that is asymmetric (one leg much worse), persists or worsens after about age 2 to 2.5, is associated with pain, or comes with short stature. These deserve attention because untreated Blount’s progressively worsens and can permanently damage the knee, whereas catching it early allows simpler treatment to steer growth straight.

How it is diagnosed

The evaluation starts with a physical exam. For a healthy child under 2 with symmetric bowing, observation with follow-up before age 3 is usually all that is needed. A standing alignment X-ray (hips to ankles) is recommended when bowing is asymmetric, persists or worsens after about age 2.5, or is accompanied by short stature — it can show Blount’s disease or rickets. Blood tests are added if rickets is suspected.

Treatment

Physiologic bowing needs no treatment beyond reassurance and time — it straightens with growth. Infantile Blount’s disease may be treated with bracing in young toddlers, with surgery (a guided-growth procedure or an osteotomy to realign the bone) if bracing does not correct it or the child is older. Adolescent Blount’s usually requires surgery. Rickets is treated by correcting the underlying deficiency, sometimes along with bracing or surgery for the deformity.

Recovery and long-term outlook

Children with physiologic bowing go on to have normal, straight legs. With Blount’s disease, the outlook is good when it is caught and treated early; because it can recur as the child grows, these children are followed until skeletal maturity.

When to call the doctor

Contact the office if your child’s bowing is clearly worse on one side, is not improving (or is worsening) after age 2, is associated with pain, or comes with unusually short stature — these warrant evaluation.

Learn more

OrthoInfo (AAOS) — Bowed Legs (Genu Varum, Blount’s Disease): orthoinfo.aaos.org

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.