Bowlegs and knock-knees are the two major types of knee deformities. They are birth defects.
Birth defects, also called congenital anomalies, are physical abnormalities that occur before a baby is born. "Congenital" means "present at birth." (See also Introduction to Birth Defects of the Face, Bones, Joints, and Muscles.)
Bowlegs
In bowlegs, what doctors call genu varum, the legs appear curved out at the knees so that the knees are more widely separated than normal. This appearance is usually created by the position of the legs in the uterus before birth. This disorder is common among toddlers and usually resolves without treatment by the time the toddler is 18 months old. If bowlegs persists or becomes more severe, doctors need to rule out rickets or other metabolic bone diseases.
Doctors may also suspect Blount disease, which is caused by a problem with the growth plate in the shinbone (tibia). Blount disease can affect one or both legs. Most commonly, it appears after the first year of life. However, it can develop in adolescence in children who are overweight. Early diagnosis of Blount disease is difficult because the problem may not show up on x-rays. Early use of splints or leg braces can be effective when started in children under 3 years of age with Blount disease. Older children may be treated with surgery.
Knock-knees
Knock-knees, what doctors call genu valgum, is less common than bowlegs. In knock-knees, the knees point inward. Even if severe, knock-knees usually resolves without treatment by the time the child is 9 years old. Children older than 10 years with severe knock-knees may need surgery.
