Load. Outside or internal forces acting on a body.
Mechanical Stress (Stress). The internal reaction or resistance to an external load.
Mechanical Strain (Strain). Extent of deformation of tissue under loading.
Yield Point. Elastic tissue limit.
Mechanical Failure. When the yield point has been exceeded, mechanical failure occurs, resulting in tissue damage.
The FIVE MECHANICAL STRESSES that can lead to sports injuries are: tension, stretching, compression, shearing, and bending.
1. Tension is that force that pulls or stretches tissue.
2. Stretching beyond the yield point leads to rupturing of soft tissue or fracturing of a bone. Examples of stretching injuries are sprains, strains, and avulsion fractures.
3. Compression is a force that, with enough energy, crushes of the tissue.
4. Shearing is a force that moves across parallel organization of the tissue.
5. Bending is a force on a horizontal beam or bone that places stresses within the structure, causing it to bend or strain.
The skin, the integument, is the external covering of the body. It represents the bodys largest organ system and consists of two layers- the epidermis and the dermis. Because of the soft and pliable nature of the skin, it can be easily traumatized.
Injurious mechanical forces can adversely affect the skins integrity. These forces are FRICTION OR RUBBING, SCRAPING, COMPRESSION OR PRESSURE, TEARING, CUTTING, AND PENETRATION.
SKIN WOUND CLASSIFICATIONS
1. Friction blister. Continuous rubbing over the surface of the skin causes a collection of fluid below or within the epidermal layer called a blister.
2. Abrasion. Abrasions are common conditions in which the skin is scraped against a rough surface. The epidermis and dermis are worn away, exposing numerous blood capillaries.
3. Skin bruise. When a blow compresses or crushes the skin surface and produces bleeding under the skin, the condition is identified as a bruise, or contusion.
4. Laceration. A laceration is a wound in which the flesh has been irregularly torn.
5. Skin avulsion. Skin that is torn by the same mechanism as a laceration to the extent that tissue is completely ripped from its source is an avulsion injury.
6. Incision. An incision wound is one in which the skin has been sharply cut.
7. Puncture wound. Puncture wound, as the name implies, are penetrations of the skin by a sharp object.
SKELETAL MUSCLE INJURIES
Acute Muscle Injuries
Contusion. A bruise, or contusion, is received because of a sudden traumatic blow to the body. The intensity of a contusion can range from superficial to deep tissue compression and hemorrhage.
Strain. A strain is a stretch, tear, or rip in the muscle or adjacent tissue such as the fascia or muscle tendons. Most often a strain is produced by an abnormal muscular contraction. A strain can range from a minute separation of connective tissue and muscle fibers to complete tendinous avulsion or muscle rupture (grade 1, 2, 3).
A grade 1 strain is accompanied by local pain, which is increased by tension of the muscle, and a minor loss of strength. There is mild swelling, ecchymosis, and local tenderness.
A grade 2 strain is similar to the mild strain, but has moderate signs and symptoms and impaired muscle function.
A grade 3 strain has signs and symptoms that are severe, with a loss of muscle function and, commonly, a palpable defect in the muscle. The muscles that have the highest incidence of strains in sports are the hamstring groups, gastrocnemius, quadriceps group, hip flexors, hip adductor group, spinalis group of the back, deltoid, and rotator cuff group of the shoulder.
The tendon contains wavy parallel collagenous fibers that are organized in bundles surrounded by a gelatinous material that decreases friction. A tendon attaches a muscle to a bone and concentrates a pulling force in a limited area. Tendons can produce and maintain a pull from 8,700 to 18,000 pounds per square inch. When a tendon is loaded by tension, the wavy collagenous fibers returns to its original shape. A breaking point of tendons occurs after a 6 percent to 8 percent increase in length. Because a tendon is usually double the strength of the muscle it serves, tears commonly occur at the belly, musculotendinous junction, or bony attachment.
Muscle Cramps and Spasms
Muscle cramps and spasms lead to muscle and tendon injuries. A cramp is a painful involuntary contraction of a skeletal muscle or muscle group. Cramps have been attributed to a lack of water or other electrolytes in reaction to muscle system. The two types pf cramps or spasms are the clonic type, with alternating involuntary muscular contraction and relaxation in quick succession, and the tonic type, with rigid muscle contraction that lasts a period of time. Muscle cramps or spasms may lead to a muscle strain.
Overexertion Muscle Problems
Muscle soreness. Overexertion in strenuous muscular exercise often results in muscular pain. Most people, at one time or another, have experienced muscle soreness, usually resulting from some physical activity to which they are unaccustomed.
There are two types of muscle soreness. The first type is acute-onset muscle soreness, which accompanies fatigue. This muscle pain is transient and occurs during and immediately after exercise. The second type of soreness involves delayed muscle pain that appears approximately twelve hours after injury. This delayed-onset muscle soreness becomes most intense after twenty-four to forty-eight hours and then gradually subsides so that the muscle becomes symptom-free after three to four days. This second type of pain is described as a syndrome of delayed muscle pain leading to increased muscle tension, swelling, stiffness, and resistance to stretching.
Delayed-onset muscle soreness is thought to result from several possible causes. It may occur from very small tears in the muscle tissue, which seems to be more likely with eccentric or isometric contractions. It may also occur because of disruption of the connective tissue that holds muscle tendon fiber together.
Muscle soreness may be prevented by beginning an exercise at a moderate level and gradually increasing the intensity of the exercise over time. Treatment of muscle soreness usually involves static or PNF stretching activities. Muscle soreness can be treated with ice applied within the first forty-eight to seventy-two hours.
Muscle stiffness. Muscle stiffness does not produce pain. It occurs when a group of muscles have been worked hard after a long period of time. The fluids that collect in the muscles during and after exercise are absorbed into the bloodstream at a slow rate. As a result, the muscle becomes swollen, shorter, and thicker and therefore resists stretching. Light exercise, massage, and passive mobilization assist in reducing stiffness.
Muscle cramps. Like muscle soreness and stiffness, muscle cramps can be a problem related to hard conditioning. The most common cramp is tonic, in which there is continuous muscle contraction. It is caused by the bodys depletion of essential electrolytes or an interruption of synergism between opposing muscles. Clonic, or intermittent, contraction, stemming from nerve irritation, may rarely occur.
Muscle guarding. Following injury, the muscles that surround the injured area contract to, in effect, splint the area, thus minimizing pain by limiting movement. Quite often this splinting is incorrectly referred to as a muscle spasm. The terms spasm and spasticity are more correctly associated with increased tone or contractions of muscle that occur because of some upper motor neuron lesion in the brain. Thus, muscle guarding is a more appropriate term for the involuntary muscle contractions that occur in response to pain following musculoskeletal injury.
Chronic Musculotendinous Injuries
Myosistis/fasciitis. In general, the term myositis means inflammation of muscle tissue. More specifically, it can be considered a fibrositis, or connective tissue inflammation. Fascia that supports and separates muscle can also become chronically inflamed after injury. A typical example of this condition is plantar fasciitis.
Tendinitis. Tendinitis has a gradual onset, diffuse tenderness because of repeated microtraumas, and degenerative changes. Obvious signs of tendonitis are swelling and pain.
Tenosynovitis. Tenosynovitis is inflammation of the synovial sheath surrounding a tendon. In its acute state there is rapid onset, articular crepitus, and diffuse swelling. In chronic tenosynovitis the tendons become locally thickened, with pain and articular crepitus present during movement.
Atrophy and contracture. Two complications of muscle and tendon conditions are atrophy and contracture. Muscle atrophy is the wasting away of muscle tissue. Its main cause in athletes is immobilization of a body part, inactivity, or loss of nerve stimulation. A second complication in sport injuries is muscle contracture, an abnormal shortening of muscle tissue in which there is great deal of resistance to passive stretch. A contracture is associated with a joint that, because of muscle injury, has developed unyielding and resisting scar tissue.
A joint in the human body is defined as the point at which two bones join together. A joint must also transmit forces between participating bones.
The joint consists of cartilage and fibrous connective tissue. Joints are classified as:
1. (synarthrotic) - immovable
2. (amphiarthrotic) - slightly movable
3. (diarthrothic) - freely moving
Diarthrotic joints are called synovial articulations. Because if their ability to move freely and thus become more susceptible to trauma, joints are of major concern to the coach, the athletic trainer, and the team physician. Anatomical articulations consist of four features: They have a capsule or ligaments; the capsule is lined with synovial membrane; the opposing bone surfaces contain hyaline cartilage; and there is a joint space (joint cavity) containing a small amount of fluid (synovial fluid). In addition, there are nerves and blood supplied to the synovial articulation, and there are muscles that cross the joint or are intrinsic to it.
Joint a union between two bones
Ligaments are sheets or bundles of collagen fibers that form connection between two bones. Ligaments act as protective backups for the joint. Primary protection occurs from the dynamic aspect of muscles and their tendons. Ligaments are strongest in their middle and weakest at their ends. Muscles are weakest in the muscle belly and strongest at the tendons.
Synovial fluid is secreted and absorbed by the synovial membrane. Synovial fluid acts as a joint lubricant. It has the ability to vary its viscosity. During slow movements it thickens; during fast movements it thins.
Cartilage provides firm flexible support. It occurs throughout the body and consists of three types: hyaline, fibrous, and elastic. Cartilage has a bluish white or gray color and is semiopaque. It has no direct blood or nerve supply. Hyaline cartilage composes part of the nasal septum, the larynx, the trachea, the bronchi, and the articiular ends of bones of the synovial joints. Fibrocartilage makes up the vertebral disks, symphysis pubis, and menisci of the knee joint. Elastic cartilage is found in the external ear and the eustachian tube. As mentioned earlier, the ends of bones in a diarthrotic joint are covered by hyaline cartilage, which cushions the bone ends.
Synovial Joint Injury Classification
Acute joint Injuries.
The major injuries that happen to synovial joints are sprains, subluxations, and dislocations.
Sprains. The sprain, one of the most common and disabling injuries seen in sports, is a traumatic joint twist that results in stretching or total tearing of the stabilizing connective tissues.
A grade 1 sprain is characterized by some pain, minimum loss of function, mild point tenderness, little or no swelling, and no abnormal motion when tested.
With a grade 2 sprain, there is pain, moderate loss of function, swelling, and in some cases slight to moderate instability.
A grade 3 (or severe) sprain is extremely painful, with major loss of function, severe tenderness, and swelling. A grade 3 sprain may also represent a subluxation that has been reduced spontaneously.
Effusion of blood and synovial fluid into the joint cavity during a sprain produces joint swelling, local temperature increase, pain, or point tenderness, and skin discoloration (ecchymosis). Ligaments, like tendons, can experience forces that completely rupture or produce an avulsion fracture.
Acute synovitis. The synovial membrane of a joint can be acutely injured by a contusion or sprain. Irritation of the membrane causes an increase in fluid production, and swelling occurs. The result is joint pain during motion, along with skin sensitivity from pressure at certain points. In a few days, with proper care, effusion and extravasated blood are absorbed, and swelling and pain diminish.
Subluxations, dislocations, and diastasis. Dislocations are second to fractures in terms of disabling the athlete. The highest incidence of dislocation involves the fingers and, next, the shoulder joint. Dislocations, which result primarily from forces causing the joint to go beyond its normal anatomical limits, are divided into two classes: subluxation and luxations. Subluxations are partial dislocations in which an incomplete separation between two articulating bones occurs. Luxations are complete dislocations, presenting a total disunion of bone apposition between the articulating surfaces. A diastasis is of two types: a disjointing of two bones parallel to one another, such as the radius and ulna; and the rupture of a solid joint, such as the symphysis pubis. A diastasis commonly occurs with a fracture.
Several factors are important in recognizing and evaluating dislocations.
1. There is a loss of function. The athlete usually complains of having fallen or of having received a severe blow to a particular joint and then suddenly being unable to move that part.
2. Deformity is almost always apparent. Because the deformity can often be obscured by heavy musculature, it is important for the examiner to palpate the injured site to determine the loss of body contour. Comparison of the injured side with its normal counterpart often reveals distortions.
3. Swelling and point tenderness are immediately present.
At times, x-ray examination of the dislocation, as with a fracture, is the only absolute diagnostic measure. A first time dislocations should be treated as a fracture.
Bone provides shape and support for the body. Like soft tissue, bone can be traumatized during sports participation.
Bones perform five basic functions:
1. body support
2. organ protection
3. movement (through joints and levers)
4. calcium reservation
5. formation of blood cells (hematopoiesis).
Bones are classified according to their shapes. Classifications include bones that are flat, irregular, short, and long. Flat bones are in the skull, the ribs, and the scapulae; irregular bones are in the vertebral column and the skull. Short bones are primarily in the wrist and ankle. Long bones, the most commonly injured bones in sports, consist of the humerus, ulna, femur, tibia, fibula, and phalanges.
Long bones can be stressed or loaded to fail by tension, compression, bending, twisting (torsion), and shearing. These forces, either singularly or in combination, can cause a variety of fractures. For example, spiral fractures are caused by twisting, whereas oblique fractures are caused by the combined forces of axial compression, bending, and torsion. Transverse fractures occur by bending.
Another stress factor is the amount of the load. An increase in energy causes a more complex fracture. Energy is used in deforming the bone and breaking the bony tissue, and some energy becomes dissipated in adjacent soft tissue.
BONE TRAUMA CLASSIFICATION
Bone trauma can generally be classified as periostitis, acute fracture, stress fractures, and epiphyseal conditions.
Periostits. An inflammation of the periosteum (membrane covering the outer surface of bone) can result from various sports traumas, mainly contusions.
Acute bone fractures. A bone fracture can be a partial or complete interruption in a bones continuity; it can occur without external exposure or can extend through the skin, creating an external wound fracture (open fracture). Fractures can result from direct trauma; in other words, the bone breaks directly at the site where a force is applied. A fracture that occurs some distance from where force is applied is called an indirect fracture. A sudden, violent muscle contraction or repetitive abnormal stress to a bone can also cause a fracture.
Depressed fracture. Depressed fractures occur most often in flat bones such as those found in the skull. They are caused by falling and striking the head on a hard, immovable surface or being hit with a hard object. Such fractures also result in a gross pathology of soft tissue.
Greenstick fracture. Greenstick fractures are incomplete breaks in bones that have not completely ossified, such as the bones of adolescents.
Impacted fracture. Impacted fractures can result from a fall from a height, which causes a long bone to receive, directly on it long axis, a force of such magnitude that the osseous tissue is compressed.
Longitudinal fracture. Longitudinal fractures are those in which the bone splits along its length.
Oblique fracture. Oblique fractures are similar to spiral fracture. Oblique fractures occur when one end of the bone receives sudden torsion or twisting while the other end is fixed or stabilized.
Serrated fracture. Serrated fractures, in which the two bony fragments have saw-tooth, sharp-edged fracture line, are usually caused by a direct blow.
Spiral fracture. Spiral fractures have an S-shaped separation. They are common in football and skiing, sports in which the foot is firmly planted when the body is suddenly rotated in an opposing direction.
Transverse fracture. Transverse fractures occur in a straight line, more or less at right angles to the bone shaft.
Comminuted fracture. Comminuted fractures consist of three or more fragments at the fracture site.
Contrecoup fracture. Contrecoup fractures occur on the side opposite to the point at which trauma was initiated. Fracture of the skull is, at times, a contrecoup fracture.
Blowout fracture. Blowout fractures occur to the wall of the eye orbit as the result of a blow to the eye.
Avulsion fracture. An avulsion fracture is the separation of a bone fragment from its cortex at an attachment of a ligament or tendon.
Stress fractures. Stress fractures have been variously called march, fatigue, and spontaneous fractures, although stress fracture is the most common used term. The exact cause of this fracture is not know, but there are a number of likely possibilities: an overload caused by muscle contraction, an altered stress distribution in the bone accompanying muscle fatigue, a change in the ground reaction force such as movement from a wood surface to a grass surface, or performance of a rhythmically repetitive stress that leads up to a vibratory summation point. Rhythmic repetitive stress is the most favored possibility. Rhythmic muscle action performed over a period of time at a subthreshold level causes the stress-bearing capacity of the bone to be exceeded, hence, a stress fracture.
Typical causes of stress factures in sports are as follows:
1. Coming back into competition too soon after an injury or illness.
2. Going from one event to another without proper training in the second event.
3. Starting initial training too quickly.
4. Changing habits or the environment (e.g. running surfaces, the bank of a track, or shoes).
Susceptibility to fracture can also be increased by a variety of postural and foot conditions. Flatfeet, a short first metatarsal bone, or a hypermobile metatarsal region can predispose an athlete to stress fractures. The major signs of a stress fracture are swelling, focal tenderness, and pain.
Nerve trauma can be produced by overstretching or compression. Like other injuries, nerve injuries can be acute or chronic. The sudden stretch of a nerve can cause a burning sensation. A variety of traumas to nerves can produce acute pain or a chronic pain such as neuritis.
An athlete with faulty biomechanics has an increased potential for injury.