Knock Knees | Symptoms and Causes

What are the symptoms of knock knees?

A standing child of average weight whose knees touch, but whose ankles do not, is usually considered to have knock knees. An abnormal walking gait can also be a sign of the condition. The condition usually becomes apparent when a child is 2 to 3 years old, and it may increase in severity until about age 4. It usually self-corrects by the time a child is about 7 or 8 years old. But if the condition doesn’t appear until a child is 6 or older, it could be a sign that there is an underlying bone disease.

During early childhood, knock-knees actually help a child to maintain balance, particularly when the child begins to walk, or if the foot rolls inward or turns outward. When a child has knock knees, both knees usually lean inward symmetrically. One knee, however, may "knock" less than the other or may even remain straight.

Occasionally, knock knees persist into adolescence. The condition is slightly more common in girls, although boys can develop it, too.

Knock Knees at Boston Children's Hospital

What causes knock knees?

Knock knees are usually part of the normal growth and development of the lower extremities. Some cases, especially in a child who’s 6 or older, may be a sign of an underlying bone disease, such as osteomalacia or rickets. Obesity can contribute to knock knees—or can cause gait (walking) problems that resemble, but aren’t actually, knock knees. The condition can occasionally result from an injury to the growth area of the shin bone (tibia), which may result in just one knocked knee.

In the course of developing normal alignment of their lower extremities, all young children have knock knees to some degree for a period of time. At the age of 3, more than 20 percent of children have at least a 5-centimeter gap between their ankles. By the age of 7, only 1 percent of children have this gap.