DIFFERENCES IN THE TENSILE STRENGTH OF BONE OF DIFFERENT HISTOLOGICAL TYPES

[ 87 ] DIFFERENCES IN THE TENSILE STRENGTH OF BONE OF DIFFERENT HISTOLOGICAL TYPES BY J. D. CURREY Department of Zoology and Comparative Anatomy, Oxford INTRODUCTION A considerable amount of work has been done on the strength of bone (Evans & Lebow, 1951; Dempster & Liddicoat, 1952; Hulsen, 1896; for a review of the literature see Evans, 1957), and some work has been done on the strength of bone samples taken from different parts of the same bone (Olivo, Maj & Toajori, 1987). It became necessary, during the course of investigations I had been making on the structure and development of Haversian systems, to find out whether bone is strengthened or weakened by the presence of Haversian systems. It seems, however, that there is only one published work on the strength of bone of different histological types (Walmsley & Smith, 1957). In this, merely a short report of a paper read before the Anatomical Society, the authors state that they have observed differences, in Young's modulus and ultimate breaking strength, in bone of different histological types in the horse. Professor Walmsley (personal communication) writes: '. . where one gets the apparently circumferential lamellae, there is a high Young's modulus and also a high breaking stress, whereas in bone of the apparently " normal " Haversian pattern, there is a low Young's modulus and a correspondingly low breaking stress.' The present work, which shows that bone containing Haversian systems has less tensile strength than that with no Haversian systems in it, was carried out to help resolve this problem, and agrees in general with the work of Walmsley & Smith. DEFINITION OF HAVERSIAN SYSTEMS For the purposes of this study, the bone of the compacta of the diaphysis of the femora of oxen was considered to fall into one of two histological categories, either 'Haversian systems' or 'not Haversian systems'. The latter term groups together many types of bone structure; for instance, both the typical laminar bone of Artiodactyls and bone containing irregular primary osteones are included under this heading. However, all these types are characterized by the fact that they are primary. That is, they are not formed in the spaces left by the resorption of pre- viously existing bone. Typical Haversian systems, on the other hand, are formed as the result of infilling, by lamellar bone, of more or less tubular cavities which have been excavated round blood vessels. It is important to note that primary osteones are included in the category 'not Haversian systems', though in many respects they are similar to secondary osteones, which is another name for Haversian systems (Pritchard, 1956). Though these two types of structure appear rather similar under the microscope, it is in fact simple to

DIFFERENCES IN THE TENSILE STRENGTH OF BONE OF DIFFERENT HISTOLOGICAL TYPES

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