A sprain is an overstretching of supporting ligaments that results in a partial or complete tear of the ligament.11 While a strain also arises from an overstretching of the muscle-tendon unit, it is marked by damage to the muscle fibers or muscle sheath without tearing of the ligament.9,14 The key difference between a sprain and a strain is that a sprain involves damage to ligaments, whereas a strain involves damage primarily to muscle. One common example of muscle strain and sprain is low back pain.15
Overloading the muscle and connective tissue results in complete or partial tears of the skeletal muscle, tendons, or ligaments.9,14 This usually occurs when the muscle is activated in an eccentric contraction, defined as a contraction in which the muscle is being lengthened.14 Examples of this type of contraction include putting down a large, heavy laundry basket or lowering oneself from a chin-up bar. Small tears can occur in the muscle because it is lengthening while also trying to contract to support the load. This leads to rupture of blood vessels at the site of the injury, resulting in the formation of a hematoma. Within 24 to 48 hours, an inflammatory response develops.
In the inflammatory stage, macrophages remove necrotic fibers.10 However, there is some evidence that activated neutrophils also release free radicals and proteases that cause further damage to the area.16 Finally, capillaries grow into the area, and muscle fibers regenerate during the repair and remodeling phases of healing.10
FIGURE 60-1. Skeletal muscle fiber organization. Tendons attach muscle to bone. (From Widmaier EP, Raff H, Strang KT, et al., eds. Vander, Sherman, & Luciano's Human Physiology: The Mechanisms of Body Function. 9th ed. New York: McGraw-Hill; 2004: Fig. 9-1.)
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Tired Having Back Pains All The Time, But You Choose To Ignore It? Every year millions of people see their lives and favorite activities limited by back pain. They forego activities they once loved because of it and in some cases may not even be able to perform their job as well as they once could due to back pain.