Knock Knees

What is knock knees?

Knock knees (genu valgum) is a condition in which the knees tilt inward while the ankles remain spaced apart. The condition is slightly more common in girls, though boys can develop it too.

When a child has knock knees, their knees tilt inward while their ankles remain apart.

Knock knees are usually part of a child’s normal growth and development. Most young children have knock knees to some degree for a period of time, though in some children it is more visible.

In rare cases, knock knees could be a sign of an underlying bone disease, particularly when the condition appears for the first time when a child is 6 or older.

How is knock knees related to a child’s development?

Many children go through stages of bowlegs and knock knees in their early years. As their legs grow and become stronger, the vast majority of children outgrow both bowlegs and knock knees.

  • Knock knees in infants: Knock knees are not typical in infants. However, many infants have bowlegs, a condition in which both legs curve outward, up until they are about 24 months old.
  • Knock knees in toddlers: Knock knees usually become apparent when a child is 2 to 3 years old. The knees may tilt increasingly inward up until about age 4 or 5.
  • Knock knees in young children: Children’s legs usually become aligned by the time they are about 7 years old. Some children continue to have knock knees into adolescence.
This is an image of a child with bowlegs at 1 year, knock knees at 3 years, and straight alignment by age 12. 

Stages of development

What are the symptoms of knock knees?

The symptoms of knock knees are visible when a child stands with their legs straight and toes pointed forward. Symptoms include:

  • symmetric inward angulation of the knees
  • ankles remain apart while the knees are touching
  • unusual walking pattern
  • outward rotated feet

What causes knock knees?

Many children develop knock knees during early childhood. As they begin to walk, an inward tilt at the knees can help children balance. This stance also helps if one or both of their feet roll inward or turn outward.

Less often, knock knees is caused by a more serious disorder:

  • Genetic conditions such as skeletal dysplasias or metabolic bone disease such as rickets can cause knock knees.
  • Obesity can contribute to knock knees or cause gait abnormalities that resemble knock knees.
  • An injury to the growth area of the shinbone (tibia) or thighbone (femur) may result in just one inward-tilting knee.

When should parents be concerned about knock knees?

If your child has knock knees along with any of the following symptoms, they may have a more serious condition:

  • knock knees that become apparent before age 2 or after age 7
  • knock knees that become worse after age 7
  • asymmetric appearance of the legs
  • limp when walking
  • knee or hip pain
  • short stature (below the fifth percentile)

How we care for knock knees at Boston Children’s Hospital

As a national and international orthopedics referral center, our Orthopedic Center has vast experience managing all aspects of knock knees. Our Lower Extremity Program offers comprehensive assessment, diagnosis, and treatment for children and young adults with conditions affecting their lower limbs. We have extensive experience treating disorders of the feet, ankles, knees, legs, and hips. Whether the patient is an infant, child, or adolescent, our goal is to help our patients live full, independent lives.