Musculoskeletal sprains and strains

Muscle injuries occur from either direct or indirect trauma.

Predisposing factors include type of muscle architecture (i.e., pennate muscle, type II fast twitch muscle fibers, muscle-tendon units that span 2 joints), previous injury, and inadequate warm-up before exercise.

Eccentric contraction (i.e., muscle contraction associated with forcible lengthening of the contracting muscle, such as when lowering a weight or pitching a ball) causes more frequent injury.

History and physical exam are key in diagnosis and grading of the injury as grade 1 (mild), 2 (moderate), or 3 (severe with complete rupture).

Conservative treatment is all that is required for most patients with grade 1 or 2 injuries.

Imaging studies are usually not necessary but can be obtained if grade 3 rupture is suspected, or to confirm or determine associated injuries.

Strain is an injury to the muscle or musculotendinous junction, whereas sprain is an injury to the ligament. Muscle contusion occurs when a muscle is subjected to a sudden, heavy compressive force, such as a direct blow to the muscle.

In strains, an excessive tensile force subjected onto the muscle leads to the overstraining of the myofibers and consequently to a rupture near the musculotendinous junction. Muscle strains typically concern the superficial muscles working across 2 joints, such as the rectus femoris, semitendinosus, and gastrocnemius muscles.

Muscle strain usually occurs in eccentric exercise. In eccentric exercise the contracting muscle is forcibly lengthened; in concentric exercise it shortens. While concentric contractions initiate movements, eccentric contractions slow or stop them (e.g., when lowering a weight).