The musculoskeletal system translates ideas into action. Nerve impulses in the brain speed down neurologic conduits to create the finely tuned symphony of chemical reactions that translates into physical movements. These movements allow the body to negotiate our ever-changing environment. The skin, connective tissue, bones, and joints provide the scaffolding to interconnect the cells and provide a protective and nourishing environment for cellular function.
A solid understanding of the skin, connective tissue, bone, and joints, as well as a comprehensive knowledge of the interplay of tissues and joints above and below, provides the framework for building a concise history and physical examination for each patient. This first step guides further testing, imaging, and treatment. This framework also allows the practitioner the opportunity to minimize unnecessary medical costs and patient disability. These skills take years to master and, so far, have not been usurped by advances in technology. This framework is also the art by which the science of musculoskeletal medicine has advanced.
Connective tissue provides the tensile strength, elasticity, substance, and nutrients to the multitude of cells that make up the human body. One of the primary actions of connective tissue is to transmit forces for movement by reducing friction between structures and protecting the neurovascular bundles from injury. Connective tissue is made of collagen fibers and amorphous ground substance of extracellular matrix interspersed with cells (Fig. 6–1).
Cellular and extracellular components of connective tissue. (Reproduced with permission from Connective Tissue. In: Mescher AL, eds. Junqueira's Basic Histology, 14e New York, NY: McGraw-Hill; 2016.)
The extracellular matrix describes the noncellular component of tissues and comprises collagen fibers and amorphous ground substance. The extracellular matrix provides the fluid substrate and cellular scaffolding and initiates the cues for tissue adaptation.1 Fibroblasts, macrophages, and mast cells exist within the extracellular matrix and are essential for maintaining homeostasis and tissue repair.2
Collagen is the primary structural element of connective tissue that includes bone, cartilage, fascia, tendons, and ligaments. It provides tissues with a great deal of tensile strength and inextensibility. Collagen makes up 30% of the total protein mass of the extracellular matrix.1 Fibroblasts produce collagen, which organizes into fibrils, cords and sheets in line with the direction of force.1 A special property of collagen is crimp, which allows for elongation of the collagen without damage, providing shock absorption.3 Collagen fibers eventually crosslink; the greater the crosslinking, the stronger the structure, allowing for the tremendous characteristic strength of collagen structures.4 The most common collagen is known as the mature, type I collagen, which is abundant in tissues that are subject to tensile forces. (Fig. 6–2) Immature type III collagen is ...