In genu valgum, or knock-knee, there is an abnormal curvature or angulation of the lower limb with the apex of the convexity disposed medially at the level of the knee. Although usually bilateral, knock-knee may occur in only one leg.

Etiology. The mechanical axis of the lower limb passes near the center of the knee and through the femoral head. The anatomic axis of the femur and tibia of 7 or 8 degrees. The medial femoral condyle is slightly longer than the lateral, thus maintaining the horizontal plane of the knee joint despite the inward obliquity of the femur.

Valgus deformity of the knee exceeding this normal 7 degrees is seen frequently in children between the ages of 2 and 4 years and may be considered physiologic. It usually corrects spontaneously. Persistent genu valgum is sometimes seen in obese children and in patients with excessive ligamentous laxity. It occurs with the various forms of rickets and other metabolic bone dysplasias. In children, injuries to the lateral side of either the proximal tibial or distal femoral growth plates can cause a progressive valgus deformity. In adults, malunion of fractures, especially fracture of the lateral tibial plateau, may result in genu valgum. A progressive knock-knee deformity may develop from erosion of the articular cartilage on the lateral side of the knee joint in degenerative or other forms of arthritis. Other possible cause is muscle imbalance such weakness of tibialis anterior and tibialis posterior. Which lead the child the flat feet posture. This will be compensated thru a knock knee position.

Clinical picture. The diagnosis of knock-knee is made on inspection of the extended knee. The degree of valgus can be recorded as the distance between the medial malleoli when the knees are held together, or the tibiofemoral angles can be measured clinically or roentgenographically.

The patient, as viewed from the front, may stand with the knees overlapping. The gait is altered by an internal rotation of the leg and foot to prevent the knees from striking each other while passing and by an increased lateral sway of the body to carry the weight to a position directly over the foot. Pain, absent as a rule in children with knock-knee, may be severe and disabling in genu valgum associated with the chronic arthritis of later decades.

Treatment. No treatment is required for slight or moderate genu valgum in children 3 to 7 years old; their knock-knee is physiologic and undergoes spontaneous correction in the next few years.

When treatment seems advisable for young children, a 1/8-inch raise of the medial border of the heel may be helpful. In severe cases the use of a night splint may be of value. When the deformity is the result of a metabolic abnormality, successful treatment of the primary disease may result in spontaneous correction of the genu valgum.

If the child's knock-knee is caused by poor ankle feet alignment, a supramalleolar orthosis will help correct it.

In the rare severe case that persists into late childhood and shows no tendency toward spontaneous correction, osteotomy may be advisable. The level of section, determined after roentgenographic analysis of the deformity, is usually in the supracondylar region of the femur, but at times tibial and fibular osteotomy is preferable. In older patients the removal of a small wedge of bone may be helpful. Care must be taken to overcorrect slightly the valgus deformity. The external rotation, estimated from the position of the foot with respect to the patella, can often be corrected by the same osteotomy. An alternative, less reliable operation for genu valgum in later childhood consists of retarding length growth on the medial side of the knee by stapling or bone grafting across the epiphyseal plate.

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