Chapter 664 Growth and Development

Growth patterns and development in children are often unique to the individual child. Statistically, normal is defined as 95% of a population that falls within 2 standard deviations of the mean from any given measurement.

Terms to describe some common deviations from normal are listed in Table 664-1. Congenital anomalies can be categorized into production problems and packaging problems. Production problems include abnormalities caused by malformation, dysplasia, or disruption that will not spontaneously resolve. Packaging problems include deformations caused by mechanical causes including in utero positioning and molding, and they usually resolve with time.

Table 664-1 TERMINOLOGIES FOR DEVIATIONS

Growth and Development

Consideration of growth and development helps to formulate treatment strategies designed to preserve or restore normal growth potential. Growth is subject to many variables including genetics, nutrition, general health, endocrine status, mechanical forces, and physiologic age. Growth also varies between 2 anatomic regions and even between 2 bones of the same region.

Bone formation or ossification occurs in 2 different ways. In endochondral ossification, mesenchymal cells undergo chondrogenesis to form cartilage that matures to become bone. Most bones in the axial and appendicular skeleton are formed in this manner. In intramembranous ossification, osteoblasts are formed by direct differentiation of mesenchymal cells into bone. Flat bones of the skull and clavicle are examples of this pattern of bone formation.

Centers of Ossification

At the beginning of the fetal period the chondrocytes in the midshaft of the long bones form the primary centers of growth from which the bone eventually lengthens. Secondary centers of ossification appear in the chondroepiphysis and mostly appear postnatally. They direct the formation of bone throughout growth, particularly joint development. The ossification centers that are typically present at birth are the distal femur, proximal tibia, calcaneus, and talus.

Anatomic Locations: Descriptive Terms

Typical long bones are divided into the physis, eiphysis, metaphysis, diaphysis, and perichondrial ring (Fig. 664-1). The physis is the growth plate located at the end of bone. The epiphysis is typically a secondary ossification center that contributes to joint development. The metaphysis is the bone adjacent to the physis on the side away from the joint. The diaphysis is the central part or shaft of long bones. The perichondrial ring contributes to appositional growth.

Figure 664-1 Diagram showing typical long bone divisions.

The articular cartilage also contributes to the growth of the epiphysis. The perichondrial ring, which surrounds the physes, and the perichondrium around the epiphyses and periosteum, which surrounds the metaphysis and diaphyseal regions of the bone, contribute to appositional or circumferential growth. Bones without physes (pelvis, scapulae, carpals, tarsals) grow by appositional bone growth from their surrounding perichondrium and periosteum. Other bones (metacarpals, metatarsals, phalanges, spine) grow by a combination of appositional and endochondral ossification.

Important Growth and Developmental Milestones

Some important musculoskeletal growth considerations are summarized in Table 664-2.

Table 664-2 SKELETAL GROWTH CONSIDERATIONS

• Abnormal stature can be assessed as “proportionate” or “disproportionate” based on comparing the ratio of sitting height with subischial height (lower limbs).

• Normally the arm span is almost equal to standing height.

• The head is disproportionately large at birth and ratio of head height to total height is approximately 1 : 4 at birth, which changes to 1 : 7.5 at skeletal maturity.

• Lower extremities account for about 15% of height at birth and 30% at skeletal maturity.

• The rate of height and growth increase is not constant and varies with growth spurts.

• By age 5 yr, birth height usually doubles and the child is approximately 60% of adult height. The child is about 80% of final height at 9 yr. During puberty, the standing height increases by approximately 1 cm/mo.

• Bone age is more important than chronological age in determining future growth potential.

Growth Patterns in Upper and Lower Extremities

The upper extremity grows longitudinally, primarily from physes of the proximal humeral physis and the distal radial and ulnar physes. In the lower extremity, most of the longitudinal growth occurs around the knee, in the distal femoral and the proximal tibial physes (Fig. 664-2).

Figure 664-2 The contribution (%) of each physis to the overall length of the extremities.

(From Morrissy R, Weinstein S, editors: Lovell and Winter’s pediatric orthopedics, ed 5, Philadelphia, 2001, Lippincott Williams & Wilkins.)

In the hip joint, the acetabulum forms with the convergence of three primary ossification centers: ischium, ilium, and pubis.