Tensile strength of bone along and across the grain

¹ Department of Anatomy, The University of Michigan, Ann Arbor, Michigan

Standardized test specimens of cortical bone from museum specimens of tibia and mandible (dry and water soaked) were subjected to direct tension or to bending till failure. Cortical bone from the same bone was tested both along and crosswise to the predominant direction of the Haversian systems. The cross-grain ultimate tensile strength of bone is much less than the parallel-to-grain strength (–1/12 of the parallel-to-grain strength). The ultimate tensile strength of bone as tested cross grain is less than its compressive strength as tested cross grain. Data from wet and dry tests are presented, with photomicrographs of fracture regions. This provides clues regarding the weaker structural features of bone and type of failure observed. Weaker structural elements are the cement lines surrounding osteones and the planes between the lamellae of Haversian systems; differences in fibrous tearing at certain fracture edges suggest that bone is weaker parallel to rather than transverse with the predominant orientation of the collagenous fibers.