Porth's Essentials of Pathophysiology, 4e

1100

Musculoskeletal Function

U N I T 1 2

in children younger than 2 years of age. 55 It is present at birth and may fail to correct itself if children sleep on their knees with the feet turned in, or sit on in-turned feet. It is thought to be caused by genetic factors and intrauterine compression, such as an unstretched uterus during a first pregnancy or intrauterine crowding with twins or multiple fetuses. Tibial torsion improves natu- rally with growth, but this may take several years. 54 External or lateral tibial torsion is a much less com- mon disorder. It is usually seen between 4 and 7 years of age, and is often unilateral. 54 The natural growth rotates the tibia externally, and hence external tibial rotation can become worse with time. 54,55 Clinically, the patella faces outward when the foot is straight. There may be associated patellofemoral instability with knee pain. Although some correction may occur with growth, extremely symptomatic children may require surgical correction, which is usually done after 10 years of age. GenuVarum and GenuValgum Genu varum and genu valgum are common pediat- ric deformities of the knee. As children grow, lower limb alignment usually follows a predicable pattern (Fig. 43-17). Genu varum, or bowlegs, is an outward bowing of the knees greater than 1 inch when the medial malleoli of the ankles are touching. Most infants and toddlers have some bowing of their legs up to 18 months of age. If there is a large separation between the knees (>15 degrees) after 2 years of age, the child may require bracing. Genu varum can cause gait awkwardness and increased risk for sprains and fractures. The child also should be evaluated for diseases such as rickets or tibia vara (i.e., Blount disease, to be discussed). Genu valgum, or knock-knees, is a deformity in which there is decreased space between the knees. 58,59 The medial malleoli in the ankles cannot be brought in contact with each other when the knees are touch- ing. Valgum normally develops after age 24 months and is most apparent between 3 and 4 years of age (see Fig. 43-17). By 7 years of age, the lower limb is in slight valgum and changes very little thereafter. Genu valgum can be ignored up to 7 years of age, unless it is more than 15 degrees, unilateral, or associated with short stature. It usually resolves spontaneously and rarely requires treatment. Uncorrected genu valgum may cause subluxation and recurrent dislocation of the patella, with a predisposition to chondromalacia and joint pain and fatigue. If genu varum or genu valgum persists and is uncorrected, osteoarthritis may develop in adulthood as a result of abnormal intra-articular stress. Idiopathic tibia vara, or Blount disease, is an abnor- mal pathologic, developmental bowing that results from altered growth of the upper medial epiphysis 58,59 (Fig. 43-18). Although the cause of tibia vara remains unknown, it may occur secondary to growth suppres- sion from increased compression forces across the medial aspect of the knee. Blount disease is more com- mon in obese children who are early walkers. It is also more common in black children. It may be unilateral, in contrast to physiologic bowing, which is almost always

Femoral head

Femoral anteversion

Femoral condyles

Tibia

Internal tibial torsion

FIGURE 43-16. Femoral anteversion and internal tibial rotation. Femoral anteversion normally decreases from about 40 degrees at birth to 15 degrees at maturity, and internal tibial rotation from 5 degrees at birth to 15 degrees at maturity.

knees and toes point in (Fig. 43-16). Children with this problem are encouraged to sit cross-legged or in the so-called tailor position (with the knees touching and the legs folded under). If left untreated, the tibiae com- pensate by becoming externally rotated so that by 8 to 12 years of age, the knees may turn in but the feet no longer do so. A derotational osteotomy may be done in severe cases or if there is functional disability. External femoral torsion is an uncommon disorder characterized by excessive external rotation of the hip. Bilateral external torsion is usually a benign condition, and treatment is observational. When the disorder is unilateral, slipped capital femoral epiphysis should be excluded (to be discussed). 54 Tibial Torsion. Tibial rotation is determined by measur- ing the thigh–foot angle, which is done with the ankle and knee positioned at 90 degrees (see Fig. 43-15B). The angle is formed between the longitudinal axis of the femur and the longitudinal axis of the foot. Inward rotation, which is assigned a negative value, indicates internal tibial torsion, and outward rotation, which is given a positive value, represents external tibial rota- tion. Infants normally have a mean angle of −5 degrees as a consequence of normal in utero position. 54 In mid- childhood through adult life, the mean angle increases to about 10 degrees. Internal or medial tibial torsion (i.e., bowing of the tibia) is a rotation of the tibia that makes the feet appear to turn inward. It is the most common cause of intoeing