Genu Varum (Bowlegs)

If you are trying to work out whether your child's legs are normal, our page on bowlegged or knock-kneed walks through normal leg shape by age. This page covers genu varum as a condition: its causes, tests and treatment.

What genu varum means

Genu is Latin for knee. Varum (varus) describes a joint where the bone below it angles inward toward the midline, so the knee itself bows outward. The opposite, knock knees, is genu valgum.

Normal leg shape through childhood

Bowing in early childhood is called physiologic genu varum. It is symmetrical, painless, does not interfere with walking or running, and the child is of normal height. It often comes with in-toeing from a twist in the shin bone (tibial torsion), which also corrects with growth.

Causes of abnormal genu varum

Blount disease

Blount disease (tibia vara) is a growth disorder of the inner part of the growth plate at the top of the shin bone. The inside of the bone grows too slowly, so the bowing gets worse rather than better.

• Infantile (early onset): appears before age 4, often both legs. Linked to early walking and higher body weight.
• Adolescent (late onset): appears after about age 10, often one leg, mostly in children with obesity.

It can be hard to tell from normal bowing before age 2. X-rays help: doctors measure the angle at the top of the shin, and a sharp beak-like change at the inner growth plate suggests Blount disease.

Rickets

Rickets is softening of growing bones from lack of vitamin D, calcium or phosphate. Bones bend under body weight. Clues include widened wrists and ankles, delayed growth, late teeth, bone pain and muscle weakness. Causes include:

• Vitamin D deficiency, most often in breastfed infants not given vitamin D drops and children with darker skin or little sun
• Low calcium diets
• Inherited X-linked hypophosphatemia, where the kidneys waste phosphate

Other causes in children

• Injury or infection of the growth plate, causing one-sided bowing
• Skeletal dysplasias such as achondroplasia
• Some metabolic and kidney diseases affecting bone

Genu varum in adults

In adults, bowing most often comes with osteoarthritis of the knee affecting the inner (medial) side. As cartilage wears on the inner side, the joint collapses toward that side and the bowing increases. Bowing also concentrates load on the inner knee, which speeds the arthritis. Old fractures that healed out of line, and earlier childhood conditions, are other causes.

Symptoms

• Visible gap between the knees with the feet and ankles together
• A waddling or rolling walk, or in-toeing
• Frequent tripping in young children
• Knee pain on the inner side, ankle or hip pain in older children and adults
• Unequal leg length if only one side is affected

How genu varum is diagnosed

The doctor watches the child stand and walk, measures the gap between the knees with the ankles together, checks height, compares both sides and looks for signs of rickets. Questions include when the bowing started, whether it is changing, diet, vitamin D use and family history.

Tests are needed only when something does not fit normal development:

• Standing X-rays of the whole legs to measure alignment and look at the growth plates
• Blood tests for calcium, phosphate, alkaline phosphatase, vitamin D and parathyroid hormone when rickets is suspected
• Photos or measurements every few months to show whether bowing is improving

Treatment

Normal bowing

No treatment is needed. Special shoes, braces and exercises do not speed up natural correction. Recheck if it is not improving after age 2.

Blount disease

• Bracing with a knee-ankle-foot orthosis can help in mild infantile cases when started before about age 3.
• Guided growth surgery places a small plate on the outer side of the growth plate to let the inner side catch up, used in growing children.
• Osteotomy (cutting and realigning the bone) is used for severe or progressive cases, ideally before age 4 in infantile Blount disease to reduce recurrence.

Rickets

Nutritional rickets is treated with vitamin D and calcium, and mild to moderate bowing usually improves over months to a couple of years. X-linked hypophosphatemia needs specialist treatment. Surgery is considered only if deformity remains after the bones have healed.

Adults

• Weight loss and strengthening exercises reduce load and pain
• An unloader knee brace can shift weight away from the inner knee
• High tibial osteotomy can realign the leg in younger, active adults with arthritis on one side of the knee
• Knee replacement for advanced arthritis, which also straightens the leg

Outlook

Physiologic bowing corrects on its own in almost all children. Blount disease and rickets usually do well when treated early, though some children need more than one operation. Untreated significant bowing can lead to early knee arthritis.

Frequently asked questions

At what age should bow legs go away?

Most toddlers' bow legs straighten between 18 and 24 months. Many children then become knock-kneed between 3 and 4 years before reaching adult alignment by about age 7. See a doctor if bowing is still clear after age 2 to 3, is getting worse, or affects one side.

Can bow legs be corrected in adults?

Exercises and braces cannot straighten bone. They can improve muscle strength and knee pain. True correction in adults requires surgery: an osteotomy to realign the bone, or a knee replacement when arthritis is advanced. Many adults with mild bowing need no treatment.

What is the difference between Blount disease and normal bow legs?

Normal bowing is symmetrical, painless and improves after 18 months. Blount disease is a growth plate disorder that makes bowing worsen with age, is often more pronounced on one side or at the top of the shin, and shows typical changes on X-ray. It needs orthopedic treatment.

Does walking early cause bow legs?

Early walking is linked to infantile Blount disease, especially in heavier toddlers, but walking itself does not cause normal bowing. There is no need to stop a child from walking. If bowing worsens after age 2, an orthopedic check is appropriate.

Can vitamin D deficiency cause bow legs?

Yes. Lack of vitamin D causes rickets, in which soft bones bend under body weight. Breastfed babies need vitamin D drops from soon after birth, as recommended by the American Academy of Pediatrics, and children with darker skin or little sun exposure are at higher risk.