Specialized connective tissue: bone, the structural framework of the upper extremity

Abstract

Bone is a connective tissue containing cells, fibers, and ground substance. There are many functions in the body in which the bone participates, such as storing minerals, providing internal support, protecting vital organs, enabling movement, and providing attachment sites for muscles and tendons. Bone is unique because its collagen framework absorbs energy, whereas the mineral encased within the matrix allows bone to resist deformation. This article provides an overview of the structure and function of bone tissue from a macroscopic to microscopic level and discusses the physiological processes contributing to upper extremity bone health. It concludes by discussing common conditions influencing upper extremity bone health.

Figure 1

Macroscopic anatomy of a long bone. The relatively cylindrical shaft or diaphysis consists predominantly of cortical bone, whereas the expanded epiphyses have a greater proportion of trabecular bone enclosed within a relatively thinner cortical shell. Images are of a mouse femur acquired using micro-computed tomography.

Figure 2

Microscopic anatomy of bone. A) Schematic diagram of bone microstructure. B) Cortical bone osteon or Haversian system with central Haversian canal, concentric lamellae and uniformly spaced lacunae. C) Cortical bone osteon as viewed in cross section via light microscopy. D) Trabeculae shown in cross section with lamellae of bone, lacunae and outer covering of endosteum. E) Trabecular bone osteons or ‘packets’ as viewed via backscattered electron imaging. F) Light microscope image of the fibrous and cellular layers of the periosteum covering the outer surface of cortical bone. G) Light microscope image of the endosteum lining the medullary cavity and trabecular bone (Panels A, B, D reproduced with permission of the McGraw-Hill Companies from McKinley M and O’Loughlin VD: Human Anatomy (2^nd ed.). New York, NY: McGraw-Hill Higher Education, 2008. Panel E reproduced with permission of Elsevier Inc. from Roschger P, et al.: Bone mineralization density distribution in health and disease. Bone 2008;42:456–466).

Figure 3

Bone remodeling by a basic multicellular unit (BMU). A stimulus activates osteoclast precursors to differentiate and form an advancing front of actively resorbing osteoclasts. The resorptive bay created by osteoclastic bone resorption is lined by mononuclear cells (not shown) prior to the formation of osteoid (unmineralized bone matrix) by osteoblasts (Reproduced with permission of the Massachusetts Medical Society [©2007; all rights reserved] from Canalis E, et al.: Mechanisms of anabolic therapies for osteoporosis. N Engl J Med 2007;357:905–916)