Etiology
Muscle injuries can be caused by contusion, strain, or laceration.[10][11]
More than 90% of all sports-related injuries are either contusions or strains.[11]
A muscle contusion occurs when a muscle is subjected to a sudden, heavy compressive force, such as a direct blow to the muscle. This kind of muscle trauma typically takes place in contact sports, whereas sprinting and jumping are the most common activities associated with muscle strains.[10][12]
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.[12][13][14]
Ligament injuries are usually sprains and usually due to excessive tensile force leading to varying grades of sprain.
Pathophysiology
The pathophysiology of musculoskeletal sprains and strains differs, depending on the anatomical structure involved.
Muscle injuries
A muscle-tendon unit can be injured when it is either passively stretched or stretched while activated. 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. A strain injury frequently occurs in the setting of eccentric contraction. Forces generated within eccentrically activated muscle are higher than in a concentrically activated muscle, thus increasing susceptibility to injury.[15]
The healing of an injured skeletal muscle usually follows a constant pattern, irrespective of the underlying cause (contusion, strain, or laceration).[13][16]
Three phases have been identified in this process:
Destruction phase, characterized by the rupture and ensuing necrosis of the myofibers, formation of a hematoma between the ruptured muscle stumps, and inflammatory cell reaction.
Repair phase, consisting of the phagocytosis of the necrotized tissue, regeneration of the myofibers, and concomitant production of a connective tissue scar, as well as capillary ingrowth into the injured area.
Remodeling phase, a period during which regenerated myofibers mature, the scar tissue contracts and is reorganized, and the functional capacity of the muscle recovers.
Ligament injuries
Injury to a ligament, usually due to rupture of a sequential series of collagen fiber bundles, may change its structure and physiology. Ligament injury may resolve by the formation of scar tissue, which is biologically and biomechanically inferior to the ligament it replaces. Joint laxity may persist following ligament injury.[17]
Classification
Classification according to mechanism of injuries[1]
Indirect injury: muscle strain
No direct contact
Injuries occur at the musculotendinous junction
Frequently occurs in eccentric contraction. Eccentric contractions slow or stop movements (e.g., when lowering a weight).
Indirect: delayed-onset muscle soreness
Occurs 24 to 48 hours after unaccustomed exercise
Resolves in 5 to 7 days
Eccentric exercise. This type of exercise is associated with forcible lengthening of the contracting muscle.
Direct injury
Direct force
Myositis ossificans can occur.
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