Atlas of pathophysiology, 2 Edition

Part II - Disorders

Musculoskeletal disorders

Strains

A strain is an injury to a muscle-tendon unit. Sudden forceful contraction of a muscle under stretch overloads its tensile strength, resulting in failure at the muscle-tendon junction. Muscles that cross two joints are most susceptible to strain. These include the hamstrings, rectus femoris of the thigh, gastrocnemius of the calf, and biceps brachialis of the upper arm.

Causes

·   Sudden or unanticipated muscle contraction due to falling, sprinting, throwing, or other forceful activity

·   Inadequate warm-ups and conditioning

·   Degenerative changes in muscle-tendon units secondary to aging, or anabolic steroid use

Pathophysiology

Bleeding into the muscle and surrounding tissue occurs when a muscle is torn. When a tendon or muscle is torn, an inflammatory exudate develops between the torn ends. Granulation tissue grows inward from the surrounding soft tissue and cartilage. Collagen formation begins 4 to 5 days after the injury, eventually organizing fibers parallel to the lines of stress. With the aid of vascular fibrous tissue, the new tissue eventually fuses with surrounding tissues. As further reorganization takes place, the new tendon or muscle separates from the surrounding tissue and eventually becomes strong enough to withstand normal muscle strain.

If a muscle is chronically strained, calcium may deposit in the muscle, limiting movement by causing stiffness, and muscle fatigue.

Signs and symptoms

·   Pain

·   Inflammation

·   Erythema

·   Ecchymosis

·   Elevated skin temperature

Diagnostic test results

·   Stress radiography visualizes the injury in motion.

·   X-ray detects the presence of fracture.

·   Muscle biopsy, which is rarely done, shows muscle regeneration and connective tissue repair.

Treatment

·   Compression wrap

·   Elevating injured part above the level of the heart

·   Analgesics

·   Application of ice for up to 48 hours, then application of heat

·   Surgery to suture tendon or muscle ends in close approximation

Chronic strains

·   Treatment usually unnecessary

·   Heat, nonsteroidal anti-inflammatory drugs, analgesic muscle relaxants to relieve discomfort

P.237

MUSCLE STRAIN

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