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Injury Mechanisms & Types of Sports Related Injuries


Introduction


The stresses of athletic competition can be unimaginable. Football players can collide and the forces calculated can reach that of a car collision. Amazingly the body can absorb and distribute thousands of pounds of force. However, small amounts of force applied in the right manner can damage tissues. If forces reach certain thresholds within tissues, then injury will result. There are various mechanisms that account for injury in sport. Many tissues can be affected from the various mechanisms.


The type of injury, degree of injury, and the tissues affected will be a direct result of the injury mechanism. For instance, bone can sustain a variety of fractures. A fracture will result from a force applied to the bone. Depending on the amount of force, the bone may simply fracture and not affect or disrupt tissues around the fracture. However, if enough force is applied, the bone could fracture and puncture or lacerate tendons, nerves, muscles, ligaments, cartilage, blood vessels, and other tissues.


There are several factors that can contribute to or increase the risk of sport injury such as poor nutrition, poor conditioning, poor flexibility, improper equipment, playing surface, and many more. Most of the factors that contribute to injury can be avoided or eliminated.


for example, if an athlete does not maintain a proper athletic diet, then muscles and tendons may not have adequate nutrition to repair from the damage occurred during the stresses of sport. This may lead to muscle injury. Please refer to the Nutrition Section to learn more about how to eat to prevent injuries. Another example may be that of playing surface. If the playing surface is slippery, then an athlete could fall which could influence a variety of injuries.


One of the main goals of a strength and conditioning and sports medicine program should be to prevent injury. The following examples are just a few of the many ways these teams can prevent injuries. Injury prevention can be accomplished by structuring training programs to increase flexibility and condition tissues to the vigorous stresses of sports (refer to the Strength & Conditioning Section to learn more about this topic).


The sports medicine team will work with athletic surface crews to make sure all playing surfaces are safe to play on. In addition, the sports medicine team will evaluate the athletes and determine if braces, tape, or wraps should be worn over structures to add support and help prevent injuries.

Bone Injuries


The purpose of the skeletal system is to protect internal organs, provide attachment sites for muscles, and help facilitate movement. The internal architecture and external geometric make up of bones allow it to absorb and distribute forces. When these forces can’t be absorbed or dissipated then injury results. Bone is highly vascular and has the ability to self-repair.


The unique feature of bone is that it has the ability to alter its properties and internal structure in response to changes in mechanical demand. When stress is applied to bone, it causes minute electrical signals that stimulate bone remodeling and strengthening in the area of the signal. This is done through a process called Wolf’s Law.


Bone injury depends on its mechanical properties, geometric make up, the force applied to the bone, the rate of force (force is applied all at once or gradually over time), and the frequency of loading. For instance, bone injury can result from the frequency of loading. Anytime an athlete increases his/her training in large volumes, he/she will increase the risk of sustaining a fracture.


If an athlete were to suddenly increase training from one hour per day to two hours per day, then he/she may suffer bone injury. The reason being is that the athlete’s bones will suffer twice the load they are a custom to and Wolf’s Law will not have time to respond.


Another variable that may contribute to bone fractures is that of muscle fatigue. The muscles may not be in shape to handle two hours of activity. The muscle fatigue that will result during activity will cause a decrease in ability of the muscles to help absorb force. This will increase the amount of force that the bones will have to absorb and dissipate. Thus, muscle fatigue will increase an athletes risk for suffering a fracture. Therefore, athletes should gradually increase their training over a period of time.


Bones can be loaded in six different ways. Each way the bone is loaded, will influence the type of fracture sustained by the bone. Bone can withstand greater force in certain mechanisms of loading than in others. The following are the six mechanisms in which a bone can be loaded.


     Tension - Tensile loading can cause a pulling apart of the bone. Equal and opposite forces are applied away from the surface of the structure. Bone withstands greater stress in tension than in shear.


     Compression - Compressive loading is a pushing together of the bone. Equal and opposite forces are applied directly into the surface of the structure. Bone withstands greater stress in compression than in tension.


     Shear - Shear loading results from a force that is applied parallel to the surface of a structure.


     Bending - Bending causes a bone to bend about an axis. When a bone is loaded in bending, it is subjected to compression on one side of the axis (concave side) and tension on the other side (convex side) of the axis.


     Torsion - In torsion a load is applied that causes the bone to twist about an axis and torque is produced within the bone.


     Combined Loading - Combined loading is when two or more loads are applied to a bone at the same time. In the combined loading example it is compression and torsion loading the bone.


Fractures

Fractures are considered to be the breaking of bones. Names and classifications of fractures must consider the location of the fracture relative to the rest of the bone, the shape, direction, and magnitude of the fracture lines, as well as the fracture’s onset. Different fractures will produce different secondary injuries such as severing nerves, muscles, tendons, arteries, and more.


Exostosis

Wolf’s Law states that a bone will remodel itself in order to become stronger do to forces placed upon it. Exostosis is growth of extraneous bone. It can occur from a stress reaction to injury or from irregular forces on the bone. This irregular force on the bone causes an exostosis to occur at the site of stress. In some cases, it can become a mechanical block that disrupts ROM.1


Apophysitis

Apophysitis is an inflammatory condition involving a bones growth plate. Some doctors refer to it as growing pains. The growth plates are along some of the attachment sites of the larger, stronger muscle groups in the body. Tightness of the muscles, or repetitive forces applied to the bone by these muscles, can result in inflammation and separation of these areas away from the rest of the bone. This is why age and maturity is such an important factor in training and conditioning. Training and conditioning too early in life can cause harm to the athlete.1


Muscle and Tendon Injuries

When a muscle contracts and lengthens at the same time, the muscle is conducting an eccentric contraction. When a muscle contracts and shortens, the muscle is conducting a concentric contraction. These contractions are important because we are constantly moving. In movement, a joint angle will accelerate and then decelerate. For instance, when a pitcher pitches a ball, he/she moves the arm forward (concentric contractions make it go forward). Now the arm must be slowed down or else the arm will dislocate and sling out of socket from all the force of the forward motion.


This is where the eccentric muscle contraction comes into play. The muscles on the backside of the pitcher's shoulder start to eccentrically contract. These muscles are producing a force to slow the arm down, but the muscles are lengthening instead of shortening. Therefore, the arm deccelerates after the ball is released due to the eccentric contractions of the posterior shoulder muscles.


Eccentric contractions are especially important in sports injury because this is thought of as one of the precursors to muscle damage. When a muscle eccentrically contracts, it is more prone to microscopic damage. You can’t move without eccentric contractions. It is when athletes are moving at maximum speeds and exerting maximum forces that muscles tear or undergo microscopic damage.


Pitchers are usually sore after a game due to the massive amount of eccentric contractions that occur throughout a game. It takes a lot of force by the posterior shoulder muscles to deccelerate a 12 pound arm traveling at 70 mph.. Therefore, balancing the dynamics of human motion is important in keeping an athlete injury free and successful.


Injuries to a muscle belly or tendon adversely affect the muscles ability to contract fully because of a mechanical insufficiency or due to the onset of pain. If the musculotendonous (muscle and tendon) unit has been mechanically altered through partial or complete tears, then the unit may no longer be able to produce movement. Partial tears decrease force production while, complete tears do not produce any motion.



Strains

Strains to the muscle and tendon are caused by excessive stretch or tension within the muscle. Tensile (pulling apart) forces are produced when the muscle is stretched beyond its normal range of motion. This causes the muscle to tear. Muscle can also be traumatized by tension overload, which occurs when the muscle generates more force than its fibers can withstand. Depending on severity, strains are ranked from first degree (limited tearing of the muscle) to third degree (complete rupture of the muscle).


Tendonitis

Tendonitis is inflammation of the tendon. Tendonitis can result from a single traumatic force. It may also result from smaller repetitive forces being placed on the tendon. Tendonitis may also involve the synovial sheath (a thin membrane that houses synovial fluid) surrounding the tendon known as tenosynovitis. Tendonitis is a common overuse injury encountered in most sports.


Myositis Ossificans (Muscle Ossification)

Myositis Ossificans is the formation of bone within the muscle. It occurs secondary to deep contusions or muscle strains and is usually related to a fault in the body's healing process. Following an injury, osteoblasts and chondroblast (muscle and cartilage builders), form immature bone within the muscle. This injury is usually found in collision sports such as football and rugby.1

Joint and Ligament Injuries


The most prevalent of the soft tissue injuries are the injuries to the capsular (capsule that surrounds the joint) and ligamentous (hold joints together) tissues. These injuries directly affect the ability of these structures to function in a stable manner during movement.


Sprains

Sprains occur when a joint is stretched beyond its normal limits. The result is stretching or tearing of the ligaments and or joint capsule. There are three injury classifications of sprains and they are based on the amount of laxity produced by the injury relative to the opposite limb (i.e. one knee may have more laxity in it relative to the other knee because of injury). The sprains are ranked in order from first degree (little or no tearing of the ligament) to third degree (complete rupture of the ligament).


Joint Dislocation

Joint dislocations involve complete dislocation of the joints boney surfaces. The forces that cause the dislocation are usually sufficient to rupture the ligaments and capsule surrounding the joint. Dislocations result in obvious deformity and in some cases the bony structures may protrude through the skin.


Joint Subluxation

A subluxation involves the partial or complete dislocation of a joint’s boney surfaces, which may or may not suddenly return to their normal alignments. In other words the joint may pop out of place and right back in. The amount of force to cause displacement of bones is often sufficient to cause soft tissue or bony injury. Tearing of the joint capsule and ligaments as well as bone fractures will usually be associated with subluxations.


Articular Injuries

The hyaline cartilage lining a bone's articular surface is commonly injured in young athletes. In adult athletes however, damage is a result of degenerative changes. Most of these injuries are irreversible and result in chronic joint pain.


Osteoarthritis 

Osteoarthritis is the most common type of arthritis found in athletes. It is the degeneration of a joint surface. The degeneration can lead to complete destruction of the cartilage and the exposure of the subchondral bone. Flaking pieces of bone can lead to loose bodies.


Osteochondral Defects

Fractures of bones articular cartilage and the progressive softening of this cartilage are referred to as OCD’s or osteochondral defects. The severity of an OCD is based on its depth, where partial-thickness OCD’s involve the outer layering of the articular cartilage and the full-thickness OCD’s exposes the underlying bone.1


Osteochondritis Dissecans

A condition characterized by dislodged fragments of bone in the joint space. Osteochondritis dissecans is a lesion of the bone and cartilage that results in the delamination of the subchondral bone. The piece of bone may be stable or free floating in the joint. 1


Nerve Injuries

Trauma to the neurovascular structures (i.e. nerves, arteries, and veins) is often a consequence of joint dislocation, bony displacement, or concussive forces that puncture or sever the structures.


Peripheral Nerve Injury

Entrapment of the nerves is common among athletes. The closer to the CNS (spinal cord and brain) the injury occurs, the greater the symptoms. Likewise peripheral nerves distal (away from) to the spinal column have a greater probability of regeneration, than nerves proximal (closest to) to the column. In some cases a soft tissue may swell, this will cause a mechanical deformation of the nerve, and cause parathesia (numbness and tingling in the limb) and muscular weakness.


Nerves may also be injured by tensile forces or stretch injuries. These injuries are classified into three categories. Neuropraxia is the mildest form of nerve stretch injury. Axonotmesis involves a disruption of the axon and myelin sheath of the nerve. Neurotmesis is a complete disruption of the nerve and is the most severe form of nerve injury.1



Brain Injuries and Compartment Syndrome

Brain injuries and compartment syndrome are common among athletes. However, brain injuries can be catastrophic. Unfortunately as the body strikes an object and suddenly decelerates or the body suddenly accelerates, the brain and organs do not respond in a uniform fashion. For instance, think of your brain like a human in a car accident, except in this case the human does not have on a seat belt. The car stops, the human remains in motion and strikes the dash board. This same principle applies to the brain and organs, when the skull stops and strikes an object such as the ground, the brain remains in motion.


The brain will then strike the wall of the skull and damage will ensue. The brain may start to swell but there is no where for the pressure to go. Therefore, tissues are manipulated and damage occurs. Compartment syndrome injuries are similar in that swelling occurs within a compartment and manipulates tissues. This cuts off neurovascular supply to tissues distal to the injury site, and further harm to the distal tissues occurs.


Cranial Injuries

The majority of athletic head injuries are not catastrophic. However, they are the leading cause of death in sports. The most common head injury death in sport is the subdural hematoma (hematoma= pooling of blood). Researchers have indicated that repeated concussions may predispose an athlete to major head trauma. A subdural hematoma is a hemorrhage beneath the duramater of the meninges within the cranium.


In other words, it is bleeding between the brain and skull. The hematoma presses on the neurologic tissues and leads to ischemia (lack of blood flow) and death if pressure on the brainstem is not relieved. It needs to be understood that acute subdural hematomas are more susceptible after repeated minor head trauma, and that other types of cranial hematomas will not present signs for as up to as long as a week after injury.


These are very dangerous and should be taken with grave caution. Any concussion should be examined by a medical professional as soon as possible. CAT Scans and MRI’s are a great way to properly diagnose these injuries.


Compartment Syndrome Injuries

Certain regions of the body contain compartments such as those in the lower leg. The compartments are housed in fascia or incased in a cavity. In the lower leg there are four such compartments encased in fascia. When there is an injury and swelling ensues with in these compartments there is no where for the swelling to go and the compartments do not stretch. The swelling causes the occlusion of blood vessels. Athletes will feel numbness and tingling in the regions below the injury site. THIS IS A MEDICAL EMERGENCY. It will not seem like much or look like much, but the blood supply will be cut off do to the pressure. Soon after the blood is cut off, tissue will start to die. Get the athlete to the hospital as fast as possible.


Thermal Injuries

Thermal injury can be caused by an increase or decrease in temperature, wind or no wind, increase in humidity, cloud cover or no cloud cover, and a few other minor factors. Thermal injury affects athletes everyday that they are exposed to the drastic changes in temperature. The medical staff should notice if the weather conditions are favorable for thermal injury and address the athletes and coaches accordingly.


Hyperthermia

Hyperthermia is an elevated body temperature above the normal 98-100 degrees F. Hyperthermia occurs when external heat loss does not match internal heat production and the body becomes overheated. When the body becomes overheated, it can result in a thermal injury. A thermal injury is one that usually is a complication of heat exhaustion, heat cramps, or heat stroke.


Heat Cramps

Heat cramps are painful muscle spasms usually occurring in the calf and abdominal muscles. Sometimes heat cramps are found in upper extremity muscles. They usually result from extensive exercise in the heat were athletes may be dehydrated and electrolyte depleted. Athletes may predispose themselves to heat cramps when they are using diuretics, are not acclimated, sodium depleted (hyponatremia), and sick (fluids lost to diarrhea and vomiting). Heat cramps will usually subside quickly as long as the athlete ingests fluids.


Heat Exhaustion

Heat exhaustion usually occurs in the summer. Most of the time heat exhaustion occurs in the preseason training sessions. This is because athletes are worked hard, they are out of shape, and they are not acclimatized to the heat. Athletes that have to wear a lot of equipment like football players, baseball/softball catchers, lacrosse players, and such are at higher risk for heat exhaustion. The thick clothes make it hard for them to thermoregulate.


Symptoms will onset due to the increased metabolic heat load from the physical activity, reduced blood volume due to dehydration, and salt depletion secondary to fluid loss. Symptoms will include a core temperature up to 103 degrees F, fatigue, weakness, dizziness, nausea or vomiting, headache, low blood pressure, and more. If an athlete feels any of these symptoms, he/she should immediately see the medical team.


Heat Stroke

Heat stroke is uncommon but is the most serious of the heat related illnesses. In football, heat stroke is second to head injuries as the most common cause of death. Heat stroke is seen in endurance sports or sports where activity is prolonged for an extended period of time. High heat, direct sun light, and high humidity are optimal conditions for heat stroke.


These are a deadly combination of conditions and athletes should be given lots of fluids and cool down periods. Due to dehydration the blood plasma volume falls and the heart has to work harder to pump blood. The thermoregulatory systems are overloaded and the bodies cooling mechanisms fail. Sweating stops to conserve water loss, and the skin becomes hot and dry.


If the temperature continues to elevate (105 or higher) then permanent brain damage can occur. If the situation is not reversed, then the situation may turn fatal.The best thing to do if there is no medical team, is to shade the athlete, fan the athlete, and put cold compresses and ice in places were the major blood vessels are superficial (i.e. arm pits, groin, behind the knees, elbows, etc.). This is a medical emergency, ACTIVATE EMS AND TRANSPORT IMMEDIATELY.


Hypothermia

Hypothermia results when the core temperature begins to drop below the normal 98.6 degrees. Cold weather can decrease circulating blood temperature. Heat promoting mechanisms like shivering (produces mechanical heat from muscle friction) attempts to bring core temperature back up. Blood is shunted away from the skin and kept at a depth under the subcutaneous layer of fat (insulation). This reduces heat loss. There are two types of hypothermia.


One is a decrease in the shell temperature (temp around body’s edges) which can involve frostbite. The other is a decrease in the core temperature and shell temperature which leads to overall body cooling. The ideal conditions for hyperthermia are wet, cold, cloud cover or no sunlight, wind, and inadequate clothing just to name a few. Avoid these conditions at all cost. Hypothermia is a fatal state that can strike quickly.


Frostbite

Frostbite is the freezing of soft tissues. There are two types of frostbite one is superficial and the other effects deeper layers of tissue. Frostbite results in destruction of tissues. Damage depends on depth and penetration of the cold. Factors that may affect the damage are wet and icy skin conditions, wind chill, duration of the cold, and temperature. Affected areas usually include the ears, toes, fingers, and nose. Properly shielding these areas from the cold during athletic activity will help prevent frostbite.


Vessel Injuries

Blood vessels are often injured in sport. Depending on the amount of damage to the specific vessel, where the vessel lies in the circulatory system, and what the vessel supplies, will depict the severity of the injury. Blood vessels can rupture due to punctures by bones or other objects, blunt force, or a number of other mechanisms.


When blood vessels are damaged, swelling will ensue. The most dangerous areas for blood vessels to rupture are the brain, lower leg, organs, and any major artery. If a vessel is completely ruptured, it will not supply blood distal to the injury site. Thus, the distal area will become ischemic and possibility necrotic. Blood vessel injuries can be very dangerous and should be seen by a physician.


Skin Injuries

Athletes suffer all types of skin injuries from sunburns to lacerations. These injuries can decrease an athlete’s performance significantly or it may cause them to stay out of competition. The mechanism of injury for the skin is usually caused by impact. Athletes may fall on the ground, get kicked, punched, stepped on, or any other mechanism that may cause a laceration, abrasion, or other skin injury. The major problem with athletes suffering skin injuries is that athletes are at an increased risk of infection. Infection will further complicate the injury and the athlete may have to take a round of antibiotics.


Eye Injuries

Athletes who play in sports where balls, sticks, pucks, punching, or kicking are involved, run a high risk of suffering an eye injury. If an eye injury is severe, it can devastate an athlete’s career. Eyes can suffer scratches, lacerations, abrasions, or blood may pool in the anterior chamber of the eye. This may occur due to blunt force from an opponent or object. If an eye injury occurs athletes may suffer double vision, blurred vision, pain and more. Athletes in these sports should wear face shields in order to lower the risk of eye injuries.


Psychological Injuries

When an athlete suffers a traumatic injury or event in sports he/she can develop fear, anxiety, depression, or other psychological states. These psychological states can cause a decrease in performance. Often after an athlete suffers a major injury such as an ACL rupture, they fear going through the pain of the injury and the long harsh rehabilitation program. Therefore, some athletes never play sports again after the injury, while others play with the fear of the injury reoccurring. Either way traumatic events can cause a psychological injury to an athlete that can end an athletes career or decrease an athlete’s performance.


By: Craig Angle - ME.d, ME.d, ATC, CSCS

Author of the book: How to Raise a Successful Athlete

Former CEO: The Athlete Project


References:

1.  Zatsiorsky, V. M. (2002). Kinetics of Human Motion. Human Kinetics: Champaign, IL

2.  Starkey, C., & Ryan, J., (1996).Evaluation of Orthopedic and Athletic Injuries. F. A. Davis Company: Philadelphia



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