The following patient information sheet is meant to help patients and family better understand a specific pediatric orthopaedic condition. It is not meant to be comprehensive, and only reflects one viewpoint. This page does not replace a medical evaluation by a pediatric orthopaedic surgeon, and your own surgeon may have a different approach to your condition.
What are bowlegs and knock knees?
Bowlegs and knock knees are common names for genu varum (bowlegs) and genu valgum (knock knees). These are generally deformities about the knees.
The knee joint is formed by the femur (thigh bone), tibia (shin bone) and patella (kneecap). The angle between the femur and tibia determine the angle of the knee.
The radiograph to the right demonstrates an example of genu valgum. If one tried to bring the legs together, the knees would contact each other while the ankles would remain far apart. The femur and tibia bones are labeled. Generally a line connecting the center of the hip joint and the center of the ankle joint should pass through the center of the knee joint. In genu valgum, this line passes on the lateral side of the knee joint (the part of the knee joint which is farther from the opposite leg).
Are bowlegs and knock knees normal?
Bowlegs and knock knees are generally normal findings in young children. Almost all babies are born with bowlegs. With natural growth, children generally convert to knock knees between 1 and 2 years of age. Knock knees are most prominent at 2 to 3 years of age, and then generally decrease to normal alignment at about 6 years of age.
As adults, people vary as to whether they have straight legs, bowlegs or knock knees. You can test yourself by straightening your legs and then bring them together. If your knees touch first, then you have knock knees, with the space between your ankles representing the severity. If your ankles touch first, then you have bowlegs, with the space between your knees representing the severity. If both your knees and ankles touch at the same time, then your legs are straight. Most adults have mild bowlegs with a small space between their knees when their ankles touch.
When should bowlegs and knock knees be treated?
Some children have a special type of bowlegs referred to as Blount's disease. This occurs when a portion of the growth plate in the tibia bone does not grow properly.
Although most orthopaedic surgeons would agree that severe bowlegs or knock knees should be treated, while mild amounts should be observed, there are no clear angular measurement cutoffs to define who is mild, moderate or severe. One of my current research interests is to try to determine what degree of knee angulation is associated with the development of arthritis in the future.
Without hard values for guidance, treatment for bowlegs or knock knees is generally reserved for a child with the following characteristics:
1. The child should have symptoms in the knees. Generally, the child will have pain in the knees, although sometimes the only finding is an awkward movement of the knee during walking called a lateral thrust.
2. The severity of the bowlegs or knock knees should be persistent or worsening. It is common to get x-rays about six months apart to see if the angulation is getting better or worse on its own. If it is improving, then it should be observed. If the child has completed growth in the knees (generally around age 14 years in girls, 16 years in boys), then this criteria does not apply.
What treatments are available?
Non-surgical treatments include physical therapy to strengthen the knee and decrease pain. While bracing is an option in toddlers with Blount's disease (see separate section on Blount's), it has limited effectiveness in straightening an older child with bowlegs or knock knees.
As noted above, surgical treatments are considered when a child is having pain or difficulty walking, and is not improving with growth or is already full grown in the knee region.
In a growing child, guided growth can be an effective option involving a mild surgery. Small plates and screws are placed on one end of the bone to temporarily prevent growth on that side. With time the other side of the bone does grow, and the overall effect is that the bone grows unevenly and straightens out the deformity. When the time is appropriate, the plate and screws is removed with a minor surgery. In some children the deformity can "rebound" after the plate and screws is removed, and additional treatments may be necessary. Please see my separate section on guided growth.
In a child who is full grown in the knee region, straightening can only occur with an osteotomy, where the bone is cut and then placed into a corrected position. This is a more significant surgery, and can be accomplished either with plate and screw fixation on the inside, or an external fixator on the outside. The choice of fixation depends on the complexity of the deformity.