Functions of the Haversian system.

The Haversian system or osteone has been traditionally adopted as a universal unit of structure in compact bone. The basic functions and the structural significance of primary and secondary Haversian tissue, however, are poorly understood. Two explanations on the functional meaning of the secondary Haversian system have been proposed. These are (a ) the interpretation of the osteone as an exclusive response to stress, and (b) the interpretation of the secondary osteone as an exclusive structural result of mineral mobilization and redistribution. However, the characteristic absence of the Haversian system in the compact bone of many vertebrate species, including widely used experimental forms such as the white rat, and the characteristic patterns of distribution of Haversian systems in the bone of those species which do possess these structural systems, cannot be entirely explained on the basis of these existing functional concepts. This report will propose that the Haversian system has several basic, previously unrecognized functions. The bone tissues from a large number of individuals and from a variety of species were studied in an attempt to establish the developmental, functional, and structural relationships which are associated with the process of secondary Haversian reconstruction. It was found that localized or widespread areas of lion-pathological osteocyte necrosis can be present as a natural condition in specific types of bony tissue, and that resorptive and reconstructive activity may be associated with such regions. It is suggested that the secondary osteone can function as a replacement mechanism in the internal reconstruction and reorganization of primary bone in cortical areas involving necrosis. A variety of the secondary osteone, independent of necrosis, is characteristically associated with areas of re-location in muscle attachment on a growing bone, and in remodeling processes involving resorption of periosteal bone surfaces during nietaphyseal reduction in diameter axd regional changes in shape. The hypothesis is advanced that this type of Haversian system functions as an anchoring mechanism which can maintain muscle continuity and attachment with bone during such remodeling changes. All secondary osteones, regardless of particular function, are structurally comparable and represent a product of internal reconstruction within compact bone. History. Leeuwenhoek (1678) was the first to notice the microscopic canal sgstern in bone, and he reported his observations to members of the Royal Society in a series of personal communications which were later published. Soon after, Clopton Havers presented several lectures before the Royal Society in which he described in greater detail the microscopic structure of bone and joints. Havers, a versatile English physician, later compiled his extensive observations and published the first monograph, “Osteologia Nova,” dealing with the structure and function of bone as a tissue (1691). Havers did not recognize or first identify the Haversian system, but he did describe in some detail the “longitudinal and transverse pores” in compact bone. These were becoming generally known, by the middle of the eighteenth century, as the canals of Havers (Albinus, 1757). Havers suggested that canals in compact bone function to transport medullary oils in order to “mollify” the substance of the bone, and he believed that the canals located near the ends of the bone carry lubricating oils to nearby joints. These logical notions were popularly accepted and persisted for another half a century (Monro, 1763). It is in-