Musculoskeletal System

Examination of the musculoskeletal system includes inspection and palpation of bones and soft tissues, measurement of active and passive joint range of motion, and assessment of stance and gait (33-36).

Bone configuration and joint mobility change during the growing years (37,38). Full-term infants may lack as much as 25 degrees of elbow extension because of predominant flexor tone. In contrast, joint hyperextensibility and hypotonia allow increased passive motion in preterm infants. The scarf sign is a good illustration of excessive joint mobility in prema­ture babies. Holding the infant's hand, the examiner draws one arm across the chest, like a scarf, toward the contralateral shoulder. In premature infants, the elbow crosses the midline, indicating hypotonic lax­ity of the shoulder and elbow joints. Full-term neo­nates have incomplete hip extension with an average limitation of 30 degrees as a result of early flexor tone predominance (37,38). The limitation decreases to less than 10 degrees by three to six months. At birth and during early infancy, hip external rotation exceeds internal rotation (37,39). With the resolution of early hip flexion attitude, internal rotation grad­ually increases. Differences between bilateral hip abduction, apparent shortening of one leg, and asym­metric gluteal and upper thigh skin folds are highly suggestive of congenital or acquired hip dysplasia or dislocation (38). Alignment of the femoral neck in neonates is consistent with prenatal coxa valga and increased anteversion. Femoral inclination is 160 degrees, and the angle of anteversion is 60 degrees. Respective adult measurements of 125 and 10 to 20 degrees develop postnatally and are accelerated by weight bearing.

Persistent fetal configuration in nonambulatory children with physical disabilities enhances the effect of neurogenic muscle imbalance on the hip joint and contributes to acquired hip dislocation in spina bifida and cerebral palsy. The popliteal angle is 180 degrees in the hypotonic preterm infant, compared with 90 degrees in full-term neonates. A combination of increased flexor tone and retroversion of the proximal tibia causes this limitation of knee extension in mature newborns. By 10 years, tibial retroversion resolves spontaneously. An early varus configuration of the tibia contributes to the physiologic bowleg appearance in infancy and corrects itself by two to three years of age. A systematic review of skeletal development, with examination of the spine and extremities, is presented in Chapter 14.

Normal variations of stance and gait should not be mistaken for pathology in the growing child (35,40,41). Gait abnormalities evident on clinical observation include asymmetric stride length and stance phase in hemiparesis; toe walking and scissoring with lower extremity spasticity; crouch posture and gait in diple- gic cerebral palsy; Trendelenburg's gait in motor unit diseases and hip dislocation; gastrocnemius limp with lack of push-off in L4-L5 weakness due to spina bifida; and various types of gait deviations associated with involuntary movements, such as ataxia, tremor, or dyskinesias, in dysfunction of the central nervous system.