Disturbance of limb growth generally leads to disproportion of the body, as the normal proportions of the body reflect changes in the relative size of the limbs at different ages.
The limb buds emerge as identifiable structures at about four weeks of embryonic development. Normal development depends on the interactions of developing vascular, nerve, muscle, and bony tissues. All are interdependent and have changing patterns and relationships during development. Initially, the limb is paddle shaped with a core of mesenchyme and a covering layer of epidermis. By six weeks, hand and foot plates can be seen and condensations of hyaline cartilage that will become bone are present. Normal limb structure is established by about the end of the eighth week, and ossification begins shortly thereafter. The arms develop more rapidly than the legs and the right side slightly ahead of the left. Intrauterine movement is essential for normal development and function of limbs at birth. Normal limb length measurements at various times in gestation and in utero limb movement patterns are presented in Chapter 15.
The relative proportions of bone, skin, fat, and muscle change with age, as does the ratio of limb-to-trunk length. At birth, span is less than height and the lower segment length is much less than the upper segment. By 10 years of age, the lower segment length approximately equals that of the upper segment. The limbs continue to grow disproportionately, and the lower segment becomes longer than the trunk, so that in the adult the upper-to-lower segment ratio is less than 1.0 (see Fig. 8.55). By about 10 years of age in boys and 12 years of age in girls, the span equals the height; thereafter, it exceeds height (see Fig. 8.3).
Many skeletal dysplasias result in disproportion of the limbs or some part of the limbs; the distal (acro), middle (meso) or proximal (rhizo) segments can be most severely affected, either prenatally or postnatally. A variety of disorders demonstrate asymmetry of the body. One limb can be larger (hemihyperplasia) or smaller (hemihypoplasia) than the other.
An approach to limb evaluation must include assessment of relative proportions of various tissues (fat, muscle, etc.) and comparison with normal age-related measurements. Various indices for comparison are available but have not been included in this text.
The inspection of limbs should answer the following questions:
1. Is the general proportion of limb-to-trunk length normal?
2. Are the limbs symmetric in length?
3. Are the limbs symmetric in circumference?
4. If one arm/leg is longer than the other, which part of the limb is longer?
5. Is there evidence for muscular or vascular anomalies?
6. Is the muscle mass symmetric?
7. Are the hands and feet symmetric in size and shape?
8. Are there contractures?
9. Are the fingers and toes symmetric in length and proportionate to the rest of the limbs?
10. Are fingernails/toenails present?
11. Do the nails have anomalies in size or shape?
The evaluation of the hands and feet includes examination of nails, skin (see Chapter 11) and flexion creases (Chapter 12).
The presence of incomplete separation of finger- or toe-rays is called syndactyly and can affect the skin only (cutaneous syndactyly), or the bone can be also affected (bony syndactyly).
Supernumerary digits or toes (polydactyly) can be found on the ulnar side of the hand (postaxial), the fibular side of the foot (postaxial), the radial side of the hand (preaxial), or the tibial side of the foot (preaxial); supernumerary digits can also occur between the finger rays (mesoaxial polydactyly). They can be just an appendage of soft tissue or can contain bony parts. X-ray examinations will help to clarify how much of the underlying bony tissue is involved.
Bony prominences of the limbs provide good anatomical landmarks from which to measure, so that limb measurements have been well standardized.
Terminology to describe congenital limb anomalies has been confusing. A glossary of terms to define specific anomalies is at the end of this book. We have tried to avoid diagnostic entities but to include useful descriptive terms.
Definition Span is the distance between the fingertips of the middle fingers of each hand, the arms are stretched out horizontally from the body.
Landmarks With the arms completely extended horizontally from the body, measure between the tips of the middle fingers across the back or the front of the patient (Fig. 8.2).
Position The patient may be standing or lying down with the arms completely extended.
Alternative Place the patient adjacent to a wall or blackboard, make marks at the tips of the middle fingers, and measure between the markings.
In the case of a squirming infant, the child may be placed prone on a bed or table, with the arms out to the sides. Measure across the back.
Remarks If the individual has a span greater than the standard 150 cm tape-measure, simply bring the beginning end of the tape around and place it on the 150 cm point (be careful not to use the end of the tape) and continue the measurement, adding the additional distance to 150 cm.
Figure 8.2 Measuring span.
Figure 8.2 Measuring span.
A normal span for age measurement is within 4.0 cm of the age-related median span (Fig. 8.3).
In infancy and early childhood, span is less than height. By about 10 years in males and 12 years in females, span equals height, thereafter, it exceeds height.
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