2007 Volume 2 Issue 1 Pages 1-11
Naturally occurring holes in bone called foramina are not detected as region of crack initiation or growth. Lumbar vertebrae, which are subjected to complex external loads, have considerable number of such big and small foramina. The mechanical characteristics of bone profoundly depend on the mineral content (HAp crystals) and collagen fibers alignment, where c-crystallographic axis of HAp crystals are preferentially oriented parallel to the long axis of collagen fibers. In the current work, we investigated the crystal orientation and mineral distribution around the foramen using X-rays to explore the reason of foramen not being region of crack initiation or growth to the precise level. Specimens were harvested from bovine lumbar vertebrae. The orientations of HAp crystals were determined from the diffracted intensity profile of X-rays using imaging plate. Mineral fractions were measured from the fraction of X-rays transmitted through the specimen. The tangential orientation of the crystals revealed around the foramen edge was considered as the main reinforcing parameter for the foramen. The minerals were distributed in the specimen without any predictable tendency. Hence, they were not considered as a strengthening parameter. A thicker cortical region was discovered near the surface around the upper edge of the foramen, which was also extended within the cancellous mass as a thin cylindrical cortical shell covering the foramen from inside. Such structures were regarded to result the foramen a damage resistant site.
