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CHAPTER OBJECTIVES

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At the completion of this chapter, the reader will be able to:

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  1. Describe the various types of stress that are applied to the body.

  2. Describe the various physiological processes by which the body adapts to stress.

  3. Define the various common mechanisms of injury.

  4. Describe the etiology and pathophysiology of musculoskeletal injuries associated with various types of body tissue.

  5. Outline the pathophysiology of the healing process and the various stages of healing of the various connective tissues.

  6. Describe the factors that can impede the healing process.

  7. Outline the more common surgical procedures available for musculoskeletal injuries.

  8. Outline the principles behind postsurgical rehabilitation.

  9. Describe the detrimental effects of immobilization.

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OVERVIEW

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Tissues in the body are designed to function while undergoing the stresses of everyday living. Body weight, friction, and air or water resistance are all types of stresses that commonly act on the body. The ability of the tissues to respond to stress is due to the differing viscoelastic properties of the tissue, with each tissue responding to stress in an individual manner based on design. Maintaining the health of the various tissues is a delicate balance because insufficient, excessive, or repetitive stresses can prove deleterious. Fortunately, most tissues have an inherent ability to self-heal—a process that is an intricate phenomenon.

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THE RESPONSE OF TISSUE TO STRESS

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Kinetics is the term applied to define the forces acting on the body. Posture and movement are both governed by the body’s ability to control these forces. The same forces that move and stabilize the body also have the potential to deform and injure the body.1 A wide range of external and internal forces are either generated or resisted by the human body during daily activities. Examples of these external forces include ground reaction force, gravity, and applied force through contact. Examples of internal forces include structural tension, joint compression, and joint shear forces (Fig. 2-1). Under the right circumstances, the body can respond and adapt to these stresses. The terms stress and strain have specific mechanical meanings. Stress, or load, is defined in units of force per area, and is used to describe the type of force applied. Stress is independent of the amount of material, but is directly related to the magnitude of force and inversely related to the unit area.2 Strain is defined as the change in length of a material due to an imposed load, divided by the original length.2 The two basic types of strain are a linear strain, which causes a change in the length of a structure, and shear strain, which causes a change in the angular relationships within a structure. It is the concentration of proteoglycans in solution (see Chapter 1) that is responsible for influencing the mechanical properties of the tissue, including compressive stiffness, sheer stiffness, osmotic pressure, and the regulation of hydration.3...

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