Muscle Injuries

Skeletal muscle injuries represent great part of all traumas in sports medicine. They should be treated with necessary precaution since a failed treatment can postpone an athlete’s return to the field with weeks or even months and cause recidivism.

Types of skeletal muscle injuries

Literature study does not reveal great consensus when it comes to classifying muscle injuries, despite their clinical importance. However, the most differentiating factor is the trauma mechanism.  Muscle injuries can therefore be broadly classified as either traumatic (acute) or overuse (chronic) injuries.

Acute injuries are usually the result of a single traumatic event and cause a macro-trauma to the muscle. There is an obvious link between the cause and noticeable symptoms. They mostly occur in contact sports such as rugby, soccer and basketball because of their dynamic and high collision nature.

Overuse, chronic or exercise-induced injuries are subtler and usually occur over a longer period of time. They result from repetitive micro-trauma to the muscle. Diagnosing is more challenging since there is a less obvious link between the cause of the injury and the symptoms. 

Muscle strains

A strain to the muscle or muscle tendon is the equivalent of a sprain to ligaments. It is a contraction-induced injury in which muscle fibers tear due to extensive mechanical stress. This mostly occurs as result of a powerful eccentric contraction or overstretching of the muscle. Therefore, it is typical for non contact sports with dynamic character such as sprinting, jumping… .

Strains are categorized into 3 grades of severity:

Grade I (mild) strains affect only a limited number of fibers in the muscle. There is no decrease in strength and there is full active and passive range of motion. Pain and tenderness are often delayed to the next day.
Grade II (moderate) strains have nearly half of muscle fibers torn. Acute and significant pain is accompanied by swelling and a minor decrease in muscle strength.
Grade III (severe) strains represent complete rupture of the muscle. This means either the tendon is separated from the muscle belly or the muscle belly is actually torn in 2 parts. Severe swelling and pain and a complete loss of function are characteristic for this type of strain.

Related articles:

Hamstring Strain
Quadriceps Muscle Strain
Calf Strain
Groin strain  

Muscle contusion (bruise)

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Quadriceps muscle contusion

Exercise-induced muscle injuries

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Shin splints

Repair process

Regardless the underlying cause, the processes occurring in injured muscles tend to follow the same pattern. Functional recovery however varies from one type of injury to another. Two phases can be distinguished in the repair process.

1. The destruction phase starts with the actual trauma that causes muscle fibers to tear. Immediate necrosis of myofibers takes place due to detoriation of the sarcoplasm, a process that is halted within hours after the trauma by lysosomal vesicles forming a temporary membrane.
   
   An inflammatory process takes place as a reaction on the torn blood vessels. Specialized cells start removing necrotized parts of the fibers. 
   
   
2. In the repair and remodeling phase, the actual repair of the injured muscle takes place. Myofibers start regenerating out of satellite cells (= undifferentiated reserve cells) and a connective tissue scar is being formed in the gap between the torn muscle fibers. In the first 10 days after the trauma, this scar tissue is the weakest point of the affected muscle.  After 10 days however, eventual re-rupture will rather affect adjacent muscle tissue than the scar tissue itself, although full recovery (up to the point of preinjury strength) can take a relatively long time.
   
   Vascularisation of the injured area is a prerequisite for recovering from a muscle injury. New capillaries originate from the remainings of injured blood vessels and find their way to the center of the injured area. Early mobilization plays a very important role since it stimulates the vascularisation process. Similar wise, intramuscular nerves will regenerate to re-establish the nerve-muscle contact. 

Diagnostic procedure

Both for acute and chronic injuries, thorough anamnesis is primary in identifying muscle injuries. Particular attention for the history of occurrence of the trauma is needed. A clinical examination and testing of the muscle function together with the anamnesis are mostly sufficient for making the right diagnosis. In some cases, additional tests (MRI, X-ray, ultrasound, CT scan…) may be required to determine the extent of the injury or to identify possible additional injuries.