Clinical Manifestations. In severe childhood rickets (see Plate 3-13), growth is impaired and height is generally below the third quartile. However, unless there is concurrent severe nutritional disturbance, weight is usually normal. Affected children are apathetic and irritable and frequently remain immobile, sitting in a Buddha-like position. The head displays a number of abnormalities, including softening and deformity of the skull (craniotabes), prominence of the frontal bones (frontal bossing), and caries and enamel defects. Examination of the thorax may reveal flaring and deformity of the ribs, funnel chest (pectus excavatum) or pigeon breast, an indentation at the insertion of the diaphragm into the lower ribs (Harrison’s groove), and nodules at the costochondral junctions (rachitic rosary). Frequent manifestations are respiratory infections and a chronic cough.
Children with rickets may also have a gentle thoracic kyphosis (rachitic cat back) and a rachitic potbelly, which, together with the bowed extremities and apathetic facies, emphasize their Buddha-like appearance. Examination of the extremities also uncovers abnormalities such as symmetric enlargement of the ends of the long bones (most prominent at the elbows and wrists), bowleg (genu varum), and, less frequently, knock-knee (genu valgum). Fractures occur frequently.
Histologic Features. In patients with rickets, the histologic appearance of the epiphyseal plate is pathognomonic. Comparison of normal and rachitic epiphyseal plates in rats shows a greatly increased axial height of the epiphyseal plate (sometimes as much as 20 times), principally because of the increased number of cells in the maturation zone; the cells have lost their columnar organization and occur in profligate profusion. Both the zone of provisional calcification of the cartilage and the primary spongiosa of the metaphysis have irregular contours and lack calcific mineral deposition.
Although changes in bone structure are no less pronounced in osteomalacia, they are not specific to that disorder because similar changes may occur in several other metabolic bone disorders (most notably hyperparathyroidism and fibrous dysplasia). The cortices are thin, and the trabeculae are small and irregularly shaped, with evidence of osteoclastic resorption of bone (a mild-to-moderate secondary hyperparathyroidism is characteristic of most rachitic syndromes). The most characteristic histologic feature, however, is the presence of a wide zone of unmineralized bone, or osteoid seam, which surrounds the mineralized trabeculae. In the section shown in Plate 3-13, the mineralized bone appears dark and the osteoid seams are pink.
Radiographic Findings. Radiographic findings reflect the histologic changes: thinned cortices and rarefied medullary bone, with indistinct and fuzzy trabecular markings. However, the radiographic hallmarks are the enormously increased axial height of the epiphyseal plate and the poor definition or absence of the zone of provisional calcification, which is normally seen as a dense, white line separating the growth plate, or physis, from the metaphysis. Often noted are cupping and flaring of the ends of the long bones, usually because of a softening of the epiphyseal-metaphyseal region. Slipped capital femoral epiphysis at the widened and severely weakened plate is an occasional finding, particularly in patients with renal osteodystrophy (see Plate 3-22).
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