Richard A. Christoph
Physiology. .of..M.yscuiosk.ei.eta,L§y,stem,,in,,, Children Childhood-Patterns ..of.. inlury
FracturesAssociated ..with. .Chil.d.Abus.e Directn.Bn!ows
Twisting . . injuries
Distraction. injuries shaking.iniMri.es
Clavicle. Fracture Supracondylar Fractures Radial . . Head. .Subluxation Disorders of the Hip and Lower Extremity Slipped. . Capital. Femora!. . . Epiphysis
Transient ..Tenosynovitis.. of.the. .Hip
Acute.. Suppurative..Arthritis Structural.. Scoliosis
Selected..Rheumatologic „Dis.ord.e..rs„in.. .Children Kawasakii.nSyndrome
Henoch-Schönlein. Purpura Poststreptococcal.. Reactive. .Arthritis Acuite„.Rheumatic.. Fever Juvenile. „Rheumatoid,.. Arthritis
The child's musculoskeletal system differs from the adult's in multiple respects, reflecting the child's active growth and development. These differences relate to the patterns of injury and illness manifested by children presenting to the emergency department. In utero, fetal positioning leads to a flexor pattern in the extremities, with external rotation of the hips and internal rotation of the tibiofibular apparatus. The ankle is in dorsiflexion, and the feet are inverted. Upon the newborn's arrival, motor development progresses predictably in a rostral-to-caudal direction and in a proximal-to-distal direction. Thus, the infant achieves head and trunk control prior to extremity control. Proficiency in movements of the upper extremity precedes lower extremity control.
The joint contractures brought about by fetal positioning and motor development influence the child's gait. The child requires a broad base of support and maintains distinct flexion of hips and knees and dorsiflexion of the ankles, resulting in a high-stepping gait. The arms of the toddler are abducted at the shoulder and flexed at the elbow. The child does not develop reciprocating arm swinging until about 2 years of age.
Simultaneously with development of the central nervous system and the maturation of motor milestones and gait, the child is growing most actively in early childhood. Bone growth occurs through two types of ossification. Growth in circumference occurs at the periosteal surface, as mesenchymal cells differentiate into osteocytes, which lay down new bone in a process known as intramembranous ossification. Longitudinal growth is achieved through endochondral ossification,, consisting of a proliferation and hypertrophy of cartilage cells at a physis. An organized vascular invasion of this cartilage results in delivery of mesenchymal cells to the area, which then differentiate into osteocytes, completing the transformation of cartilage to bone.
It is helpful to think of long bones as consisting of discrete anatomic areas. Long bones may have physes, or areas of growth cartilage, at both ends (e.g., tibia and femur). Other long bones (e.g., the phalanges) have a physis at only one end. The area of the long bone between a physis and the adjacent joint is the epiphysis, and the area of bone between a physis and a point for muscle or ligamentous attachment is an apophysis. The metaphysis of a long bone represents the area of widening, or flaring, of the long bone between its midshaft (the diaphysis) and the physis.
The long bones of children are generally less dense and more porous than the long bones of adults. The resulting increased compliance contributes to the tendency of children's long bones to respond to mechanical stress by bowing and buckling, rather than fracturing through and through, as in adult fracture patterns. The periosteum of the diaphysis and the metaphysis is thicker in children and is continuous from the metaphysis to the epiphysis, surrounding and protecting the mechanically weaker physis. This physeal weakness is related to the reduced oxygen tension found in the hypertrophic zone of the physis, a location of frequent fractures within the physis. The physis is sensitive to alterations in the blood supply to this hypertrophic zone as well as to nutritional, hormonal, and mechanical influences.
Growth of the musculoskeletal system and its response to illness, injury, and nutrition are also influenced by the growth of muscle and connective tissues. The ligaments of children are stronger and more compliant than those of adults, often tolerating mechanical forces at the expense of apophyseal attachments or epiphyseal integrity. While the absolute number of muscle fibers is fixed at birth, the fibers of tendons can increase in number and in size. The growth of muscle through hypertrophy and the growth of tendons through hypertrophy and proliferation depend on the mechanical forces applied to them.
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