Growth slowdown and arrest lines.

Transversely oriented lines within the metaphyses and proximate diaphyses were studied in multiple specimens from cadavers and amputation specimens from skeletally immature individuals. These lines, evident as transverse trabecular bands of increased radiodensity, proved histologically to be thickened, transversely interconnected trabecular networks, with more typical, longitudinally oriented trabecular bone on either side. They appeared following a temporary slowdown or cessation of rapid longitudinal bone formation in the primary spongiosa and were parallel to the contours of the contiguous physis. When growth rates were normal, longitudinally oriented trabeculae with interspersed marrow elements predominated at the zone of transformation of cartilage to bone. However, when growth rates slowed down or were temporarily arrested, the trabeculae thickened and fused with each other transversely. When the abnormal process (e.g., fracture or systemic illness) responsible for growth retardation subsided, more rapid rates of endochondral growth and transformation resumed, forming the more characteristic normal longitudinal trabecular orientation. As the bone elongated, these transverse lines were progressively displaced from the physis. As the metaphyseal bone was remodeled to diaphyseal bone, these trabecular lines were gradually remodeled and usually disappeared completely by the time skeletal maturity was reached.