Bowlegs, Knock-knee and Blount's Disease
Angular deformities about the knees are frequently of great concern to parents. These are most apparent when the child first begins to walk. The treating physician will be able to help differentiate between those deformities which will resolve spontaneously and those which will not.
The natural history of the tibial femoral angle is one of considerable bowing (genu varum) at birth, approximately 15 degrees. There is gradual spontaneous correction to zero degrees at one and one-half to two years of age. During the next year, a knock-knee (genu valgum) alignment of 10 degrees to 12 degrees develops which gradually corrects to the normal adult value of 5 to 6 degrees of valgus at about age seven years. This process is identical in boys and girls. (Fig. 1)
Clinical assessment is often made with the legs together by measuring the distance between the knees for bowing (genu varum) and the ankles for knock knee (genu valgum) deformity. (Fig. 2) A more accurate measurement would be the tibial femoral angle as seen on the standing x-ray. The graph below, taken from a study of 1480 children, illustrates how normal varus tibial femoral angulation before age 2 changes to vaglus angulation after age 2 (see arrow). One must be careful that the legs are in neutral rotation when the x-ray is taken, as internal or external rotation will alter this angle.
Physiologic bow leg deformity should spontaneously correct by two years of age. No x-rays are usually necessary before then. Internal tibial torsion and external rotation contracture of the hips often accompany genu varum and tend to accentuate the deformity.
In most instances, this deformity is not recognized until the child begins to walk. At that time, parents can become quite concerned about the wide space between the knees, the waddling gait, and the toeing-in. X-rays show medial angulation at the junction of the proximal and middle thirds of the tibia and the lower end of the femur; medial tilting of the transverse plane of the knee joint; and sclerosis of the medial concave cortices of the tibia and femur in the absence of epiphyseal abnormality or metabolic disease.
Treatment is reassurance and observation. Shoe corrections, splints and exercise programs do not produce any change different than the normal expected spontaneous correction. Moreover, use of a Denis Browne bar might exaggerate the physiologic genu valgum and pronated feet (flatfeet) that normally occur following the spontaneous resolution of the bow leg deformity
Pathologic bow leg deformities may produce serious problems. Factors suggestive of pathologic conditions include failure of genu varum to correct by age two years, increasing deformity, unilateral bowleg, and a marked lateral thrust with weight bearing.
Blount's Disease is probably the most common cause of pathologic bow leg deformity. This is a disturbance of the medial aspect of the proximal tibial growth plate, resulting in a structural genu varum. This condition is most prevalent in blacks. The infantile form is usually bilateral, progressive, and associated with significant internal tibial torsion. Most often it is seen in obese children of short stature who walked early. The juvenile form is usually unilateral, less deforming, and without internal tibial torsion. The diagnosis can be made by measuring the metaphyseal-diaphyseal angle on a standing x-ray (Fig. 3). If this angle exceeds 14 degrees, most often the varus deformity will be progressive and represents Blount's Disease.
Treatment for Blount's disease depends upon the age of the patient and the severity of deformity. If epiphyseal change is minimal and the patient under three years old, on orthosis (brace) may be effective. For older children, surgery will be required. Other rarer causes of pathologic bow leg deformity are rickets, meta-physeal dysplasia, osteochondromatosis, fibrous dysplasia, multiple epiphyseal dysplasia and osteomyelitis.
Physiologic knock knee deformity is very common in children aged three to five years. In most instances, there will be spontaneous correction by age seven to eight. Very little spontaneous improvement occurs after age eight years. Persistence of the problem may be related to laxity of the medial collateral knee ligament; quadriceps muscle insufficiency, which fails to support the medial collateral ligament; and obesity. These factors can allow valgus positioning of the knee and excessive pressure on the lateral side of the epiphyseal plate. This, over time, can result in retarded growth of the lateral femoral condyle and relative overgrowth of the medial femoral condyle. If the knee valgus is more than 15 degrees, it can cause medial foot strain, synovitis of the knee joint, patello-femoral instability, and gait abnormalities.
Most of these children demonstrate an awkward, lurching gait, their knees may rub together, and they must circumduct for clearance. Most do not run well and do poorly in physical activities. These children are considered clumsy and seem to fall more than normal.
Treatment for significant (15 degrees to 20 degrees), physiologic genu valgum may commence as soon as one is sure that spontaneous correction is not occurring. This usually will be after age five years. Initially, a knock knee brace may be tried at night time and for most of the day. If the deformity persists, a medial epiphyseal stapling or epiphyseodesis (partial growth arrest) can be carried out if there is sufficient growth potential for correction. This is most often performed in the distal femur, but can be done in the proximal tibia if the deformity appears to be arising there.
Pathologic knock knee deformities are less common. These may be related to rickets, bone tumors, and metaphyseal or epiphyseal dysplasias. An undisplaced fracture of the medial aspect of the proximal tibial metaphysis often results in the genu valgum. This may be due to an unrecognized valgus deformity at the time of fracture or growth deformity secondary to stimulation of the medial tibia. Treatment consists of a corrective osteotomy if the deformity does not remodel in 2 to 3 years. Parents should be cautioned about the possibility of this problem when the fracture is treated.
In summary, most children exhibit genu varum at birth which corrects by age two years. A significant genu valgum may occur at age three prior to spontaneous correction by age seven. No treatment is indicated unless the deformities are severe, progressive, or due to a pathologic condition. The most common cause of pathologic bow leg is Blount's Disease and of pathologic knock knee is a proximal metaphyseal fracture of the tibia. If treatment is indicated, this could be by bracing, unilateral epiphyseal arrest, high tibial osteotomy, or a combination of these.
Physiologic knock knee deformity is very common in children aged three to five years. In most instances, there will be spontaneous correction by age seven to eight. Very little spontaneous improvement occurs after age eight years.