Porth's Essentials of Pathophysiology, 4e

Disorders of the Skeletal System: Trauma, Infections, Neoplasms, and Childhood Disorders 1101

C h a p t e r 4 3

FIGURE 43-17. Lower limb alignment follows a predictable pattern. Infants typically have a gentle varum bow throughout the femur and tibia. By 18 to 24 months, the lower leg is nearly straight, with a neutral mechanical axis. Valgum gradually develops and is most apparent between 3 and 4 years of age. By 7 years of age, the lower limb is in slight valgus and changes very little thereafter. Varus should not recur, nor should valgus increase. (Adapted from Schoeneker PL, Rich MM.The lower extremity. In: Morrissy RT, Weinstein SL, eds. Lovell &Winter’s Pediatric Orthopaedics. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:1169.)

Infant

18 months

3 years

7 years

bilateral. It has been classified into three types: infantile (1 to 3 years of age), juvenile (4 to 10 years of age), and adolescent (11 years or older). The juvenile and adolescent forms are commonly combined as late-onset tibia vara. The infantile form of tibia vara, which is commonly bilateral, is the most common. Untreated infantile tibia vara is almost always progressive, with evidence of outward angulation, flexion, internal rotation, and abnormal lateral knee laxity. There is radiographic evi- dence of progressive depression of the medial metaphy- sis, the growth plate, and the epiphysis. Fusion of the metaphysis to the epiphysis may occur in severe cases. Night-brace treatment is used for mild early-onset dis- ease. Valgum rotational osteotomy of the tibia is usually indicated if angulation persists beyond 3 years of age.

Persistent tibia vara leads to early degenerative changes of the knee. Late-onset Blount disease is more common in obese boys who are of normal or greater-than-normal height. The condition may be bilateral or unilateral and char- acterized by pain rather than deformity as the primary initial complaint. 59 Radiography shows medial femoral and tibial bowing. Bracing is not practical in obese ado- lescents. Treatment includes osteotomy to realign the limb or lateral growth plate closure to allow growth to “catch up” medially. Congenital Disorders Congenital skeletal deformities can be caused by many factors, including hereditary influences, external agents that injure the fetus (e.g., radiation, alcohol, drugs, viruses), and intrauterine environmental factors. They range in severity from mild limb deformities, which are relatively common, to major limb malformations, which are relatively rare. The most common anomaly of the toes or fingers is polydactyly, or the presence of an extra digit on the hand or foot. There may also be a simple webbing of the fingers or toes (syndactyly) or the absence of a bone such as the phalanx, rib, or clavicle. Joint contractures and dislocations produce more severe deformity, as does the absence of entire bones, joints, or limbs. Osteogenesis Imperfecta Osteogenesis imperfecta, or brittle bone disease, is a hereditary disorder caused by deficiencies in the syn- thesis of type I collagen. 18,19,60,61 Although it is usually transmitted as an autosomal trait, a distinctive form of the disorder with multiple lethal defects is thought to be transmitted as an autosomal recessive trait. 19,61 In some cases, the disorder is caused by a spontaneous mutation.

FIGURE 43-18. Rotational deformity of the proximal tibia, especially when unilateral, suggests tibia vara (Blount disease).