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Which of the following statements regarding bone development and postnatal growth is correct?

A. The major long bones of the upper limbs generally have 1 physis.

B. Endochondral ossification is characterized by the replacement of osteoblasts by chondroblasts.

C. Traction or distraction may decrease physeal growth.

D. The clavicle forms by intramembranous ossification.

E. The resting (germinal) zone is the weakest physeal zone.

Answer: D

The clavicle and the flat bones of the skull are formed by intramembranous ossification. The major long bones of the upper limbs (ie, the humerus, radius, and ulna) have a physis at either end of the bone, unlike the metacarpals and phalanges, which typically have only 1 physis (Figure 207-2). Endochondral ossification is characterized by the replacement of chondroblasts by osteoblasts. Generally, excessive compression of the physis may result in decreased growth, whereas traction or distraction may accelerate growth. The germinal zone is characterized by a large amount of extracellular matrix, whereas the zone of hypertrophy and provisional calcification are more cellular and generally the weakest of the 4 zones (Figure 207-4).

FIGURE 207-2

Age of radiographic appearance of the secondary ossific centers of long-bone epiphyses: (A) upper extremity and (B) lower extremity. These appearances can be used to estimate a child's skeletal age and identify skeletal growth abnormalities and need to be differentiated from fractures. (Mark W. Kline, Rudolph’s Pediatrics, 23rd Edition. Copyright © McGraw-Hill Education. All rights reserved.)

FIGURE 207-4

Scheme of the microscopic organization of the physis or growth plate. Traditionally, the physis is separated into 4 contiguous layers from epiphysis to metaphysis: resting (or germinal), proliferative, hypertrophic, and zone of provisional calcification. (Mark W. Kline, Rudolph’s Pediatrics, 23rd Edition. Copyright © McGraw-Hill Education. All rights reserved.)

A 10-month-old female infant who was recently placed in foster care presents for a well-child visit. The foster mother expresses some concern with regard to her development. She has not previously provided foster care for infants and is not sure what to expect. She reports that the child is rolling and can sit with assistance; however, the child seems wobbly. In addition, she is concerned that she is not crawling consistently yet. Which developmental motor skill is paired correctly with the average age of achievement?

A. Sitting independently – 5 months

B. Crawling ...

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