Muscle contusion indicates a direct, blunt, compressive force to a muscle. Contusions are one of the most common sports-related injuries. [1, 2, 3] The severity of contusions ranges from simple skin contusions to muscle and bone contusions to internal organ contusions.
Although all tissue and organ contusions can result from traumatic sports injury, this article focuses on muscle contusions. Contusions of internal organs and bone contusions are not discussed in this article (see the Medscape Reference articles Concussion, Sacroiliac Joint Injury, Femur Injuries and Fractures, and Hip Pointer).
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Contusions and strain injuries comprise approximately 60-70% of all sports-related injuries. In addition, most contusion injuries go unreported and untreated. Documented muscle contusions account for one third of all sports injuries. The quadriceps and gastrocnemius muscle groups are most often involved (see the images below). [4, 5, 6, 7]
A study that compared incidence, duration of absence and characteristics of indirect (strain) and direct (contusion) quadriceps and hamstring muscle injuries reported that these thigh injuries are more frequent than have been previously described. Direct injuries (contusion) are less frequent than indirect ones (strain), and players can usually return to full activity in under half the average time for an indirect injury. 
Rotator cuff contusions of the shoulder have also been seen in professional football players. Cohen et al evaluated the incidence, treatment, and magnetic resonance imaging (MRI) appearance of players sustaining such injuries in a North American professional football team.  . The team's injury records from 1999 to 2005 were retrospectively reviewed for athletes who had sustained a rotator cuff contusion of the shoulder during in-season participation.
The investigators reported 26 players had a rotator cuff contusion, with an average of 5.5 rotator cuff contusions per season (47% of all shoulder injuries), 70.3% of which the predominant mechanism of injury was a direct blow. MRI findings included peritendon edema at the myotendinous junction, critical zone tendon edema, and subentheseal bone bruises. 
All patients were treated with a protocol involving modalities and cuff rehabilitation; 6 patients had persistent pain and weakness for at least 3 days and were given a subacromial corticosteroid injection. Overall, 3 patients (11.4%) required later surgical treatment on the shoulder. 
Cohen et al determined that rotator cuff contusions composed nearly half of all shoulder injuries in the football players in their study,  but the majority of affected athletes are able to return to sports with conservative treatment. A minority of shoulders might progress to more severe injuries such as rotator cuff tears. See the images below.
The international frequency of contusions is similar to that in the United States.
Skeletal muscle constitutes the largest tissue mass in the body, comprising up to 45% of the total body weight. Muscles that cross a single joint are located close to bone, are frequently responsible for postural maintenance, and are most susceptible to contusions. On the other hand, 2-joint muscles, such as the rectus femoris muscle, lie more superficial and are more susceptible to stretch-induced strain injury.
Contusions are caused by blunt trauma to the outer aspect of the muscle, resulting in tissue and cellular damage and bleeding deep within the muscle and between the muscle planes.  The resultant tissue necrosis and hematoma lead to inflammation.  Little is known about the role of the inflammatory process and its importance in the healing process. Clearly, too much inflammation is unfavorable, but too little may be just as devastating.
A bruise is caused by blood that has escaped from damaged capillaries into the interstitial tissues. Within a few hours after the injury, the presence of necrotic tissue and hematoma initiates an inflammatory reaction. Because inflammation initiates macrophage action with subsequent phagocytosis of necrotic debris and stimulation of capillary production, it is vital to the process of muscle regeneration. However, inflammation invariably causes edema that leads to anoxia and further cell death.
The extent of the inflammatory response is often considered excessive and detrimental to muscle regeneration. However, controversy exists regarding this theory, because some literature indicates a worsened long-term outcome in patients placed on anti-inflammatory medications. Controversy also surrounds cryotherapy, with some literature touting its benefits, whereas others question its utility. [11, 12, 13]
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