Bowlegged or Knock-Kneed: When Leg Shape Is Normal and When It Isn't

Normal leg shape through childhood

Leg alignment changes predictably as children grow:

Many parents notice bowing when a toddler starts walking, often with in-toeing. Both usually improve without treatment. Braces, special shoes and exercises do not speed up normal straightening.

How to tell if your child's leg shape is a concern

Doctors look for features that do not fit normal development:

• Asymmetry: one leg bowed or knock-kneed more than the other
• Severity: a large gap between the knees (bowing) or ankles (knock knees)
• Timing: bowing that persists or worsens after age 2, or knock knees that start after age 7
• Growth: height below the 5th percentile, or other bones affected
• Symptoms: pain, limping, frequent tripping or tiring easily

Causes of abnormal bow legs

• Blount disease: a growth disorder of the inner part of the shinbone's upper growth plate. It causes progressive bowing, often sharp just below the knee. The infantile form appears in early walkers, often heavier children who walked early. The adolescent form is linked with obesity. It does not resolve on its own.
• Rickets: soft bones from lack of vitamin D, calcium or phosphate. Signs include bowing, thick wrists and ankles, delayed walking, bone pain and poor growth. Children who are breastfed without vitamin D supplements, have darker skin, or get little sun are at higher risk. Inherited (X-linked) hypophosphatemic rickets does not respond to vitamin D alone.
• Skeletal dysplasias: inherited conditions such as achondroplasia.
• Growth plate injury or infection affecting one side of the knee.

Causes of abnormal knock knees

• obesity, which increases stress on the knee and can worsen alignment
• rickets and other bone disorders
• injury or infection near the growth plate (one-sided)
• inherited conditions affecting bone or ligaments

Bowlegged and knock-kneed in adults

In adults, leg shape usually reflects the shape you grew into. New or worsening alignment is most often caused by knee osteoarthritis. Wear of the inner part of the knee, the most common pattern, makes the knee more bowed. Wear of the outer part makes it more knock-kneed, which is more common in women and in rheumatoid arthritis. See knee arthritis.

Bow legs place more load on the inner knee, and knock knees on the outer knee and kneecap, which may raise the risk of arthritis in that compartment over decades.

Some people's knees cave inward only when they squat, land or run. That is dynamic knee valgus, a movement pattern caused by weak hip and thigh muscles rather than bone shape, and it can be retrained with exercise.

Can you be bowlegged and knock-kneed at the same time?

Yes, in two ways:

1. Windswept deformity: one leg is bowed and the other knock-kneed, so both knees point to the same side, as if blown by the wind. It is uncommon and usually signals rickets, Blount disease, a skeletal dysplasia or uneven arthritis. It needs a specialist assessment.
2. Mixed alignment within one leg: for example, bowing of the shinbone with knock knee at the knee joint itself, or a person who looks bowlegged standing but whose knees cave inward when squatting (dynamic valgus).

How leg alignment is assessed

A doctor will measure the gap between the knees or ankles with the child standing, compare both legs, check height and weight, watch the child walk, and look for signs of rickets. They may order:

• Standing X-rays of the legs to measure angles and look at the growth plates
• Blood tests for vitamin D, calcium, phosphate and alkaline phosphatase if rickets is suspected
• Repeat measurements every 6 to 12 months to track change

Treatment

• Normal physiological bowing or knock knees: observation only. No braces, shoes or exercises are needed.
• Rickets: vitamin D and calcium supplements correct most nutritional rickets, and legs often straighten with time. Inherited forms need specialist treatment.
• Blount disease: bracing may help in children under about 3. Older children often need surgery.
• Guided growth surgery: in a growing child, a small plate or screw on one side of the growth plate slows growth on that side and gradually straightens the leg. It is minor surgery.
• Osteotomy: cutting and realigning the bone for adults or older teens with severe deformity.
• Adults with arthritis: weight management, strengthening exercises, bracing or insoles, and osteotomy or knee replacement for advanced disease.

Frequently asked questions

When do bow legs correct in toddlers?

Most bow legs in toddlers straighten between 18 and 24 months as the child walks. By age 3 to 4, many children swing the other way into mild knock knees. See a doctor if bowing worsens after age 2, affects one leg more, or comes with short stature or pain.

Can I be bowlegged and knock-kneed both?

Yes. One leg can be bowed while the other is knock-kneed, called windswept deformity, which usually has an underlying cause such as rickets or Blount disease. A person can also look bowlegged standing but have knees that cave inward during movement because of weak hip muscles.

Do braces or special shoes fix bow legs?

For normal childhood bowing, no. Braces and corrective shoes do not change the natural course, which is to straighten with growth. Bracing is used only for specific conditions such as early Blount disease, under specialist care.

Can adults fix bow legs or knock knees?

Exercise cannot change bone shape, but strengthening hip and thigh muscles can improve how the knees track and reduce pain. Significant deformity causing pain or arthritis can be corrected surgically with an osteotomy or, in advanced arthritis, a knee replacement.

Is knock knee caused by vitamin D deficiency?

Vitamin D deficiency can cause rickets, which bends soft bones into bow legs or knock knees. Most knock knees in children aged 3 to 7, however, are normal development. A doctor can check vitamin D and other blood tests if rickets is suspected.