BONE MODELING AND REMODELING IN THE SKELETON OF A SUPERNUMERARY DIGIT OF A CHILD AFFECTED BY SEGMENTAL GIGANTISM.
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文摘
The present paper deals with bone modeling and remodeling in a metatarsal bone of a 6th supernumerary digit in a 3-year-old child affected by Cutis Marmorata Telangiectatica Congenita. The patient showed hypertrophy of the right thigh, leg and foot, and post-axial exadactylism of the right foot and hand. The metatarsal bone soon after surgical excision was fixed in 4 % buffered paraformaldehyde for 3 hours and methylacrylate embedded. Ground sections (50μm thick), taken from various levels of the shaft, were microradiographed (Italstructures Microradiograph: 1.7 Kw, 18 mA). Analyses were performed by light microscope under transmitted and polarized light on unstained sections and their microradiographs. An intense apposition of primary woven bone was found on the periosteal surface of the supernumerary metatarsus, not accompanied by endosteal osteoclastic resorption, as usually occurs during normal bone modeling. As a consequence the shaft displayed an abnormous thick cortex and a relatively narrow medullary canal. Osteoclastic activity, not followed by bone formation, appeared to be particularly high inside the cortex; this led to the formation of several large reserption cavities, which gave the diaphysis a spongy architecture. Bone structure and mineralization appeared qualitatively normal. These observations show that both processes of bone modeling and bone remodeling took place in an abnormal manner in the supernumerary metatarsus. In bone modeling osteoblast activity is not paralleled by osteoclast resorption, whereas in bone remodeling osteoclastic resorption is not followed by osteon formation. Since the external size of the supernumerary metacarpus seems to exceed mechanical demand, owing to congenital abnormality, and considering that the phalanx in which it is contained likely is partially unloaded, the osteoporotic appearance of the cortex seems to depend on mechanical disuse rather than on congenital abnormality.