Knock-knee (or genu valgum) is a condition where the legs are bowed inwards in the standing position. The bowing usually occurs at or around the knee, so that on standing with the knees together, the feet are far apart.
Bow-Legs This is almost always caused by softening of the bones, as in rickets. The bending occurs in the bones of both the leg and thigh, and the location of the point of greatest bending is sometimes low down toward the ankles or close up to the knee-joint, or the whole diaphysis of the bones may be curved. They are often curved anteroposteriorly as well as laterally.
Knock-knee (Genu Valgum). This condition has its point of bending most marked at the knee-joint. When caused by rickets the joint surfaces are often not much altered and the deformity is produced by a bending of the tibia or femur close to the joint; hence when an osteotomy is performed just above the condyles of the femur the joint is again brought level and resumes its functions normally.
Most people have some degree of bowleg or knock-knee and is considered within the limits of normal structure and function. During development in the first few years of life, because of rapid and differential growth around the knees, most children are bowlegged from birth till age 3, then become knock-kneed till age 5, then straighten up by age 6 or 7. In most children, even as they grow through these phases, the bowleg and knock-knee are not severe, and do not engender concern on the part of the parents. In some instances, the bowleg or knock-knee gets quite obvious, and becomes worrisome for the parents.
There are, of course, more serious causes of bowleg and knock-knee. They include the following:
1. Blount’s disease - a condition of severe bowleg that occurs usually in black children that is progressive, and may require surrgery.
2. Growth disturbance - or epiphyseal dysplasia, which may be a part of a generalized bone growth disturbance.
3. Post-trauma - where injury to the knee causes damage to the growth plate (also called the epiphyseal plate) and abnormal growth around the knee.
4. Rickets. Lack of vitamin D intake, or inability to metabolize Vitamin D due to kidney disease can cause growth disturbance of the bones in the body, including the knee.