Chapter 9: Mechanisms and Characteristics of Sports Trauma

Mechanical Injury

• Trauma is defined as physical injury or wound sustained in sport, produced by internal or external force

• Mechanical injury results from force or mechanical energy that changes state of rest or uniform motion of matter

• Injury in sports can be the result of external forces directed on the body or can occur within the body internally

• Tissue Properties– Relative abilities to resist a particular load– Strength, pressure of power is used to imply force (defined as a

push or pull)– Load can be a singular or group of outside internal forces acting

on the body.– Stress is resistance to a load– Body tissues are viscoelastic and contain both viscous and elastic

properties– Point at which elasticity is almost exceeded is the yield point– When exceeded mechanical failure occurs resulting in damage

• Tissue Stresses– Tension (force that pulls and stretches tissue)– Stretching (pull beyond yield point resulting in

damage)– Compression (force that results in tissue crush)– Shearing (force that moves across the parallel

organization of tissue)– Bending (force on a horizontal beam that places

stress within the structure

Soft Tissue Trauma

• Soft tissue or non -bony tissue is categorized as inert (noncontractile) and contractile tissue

• Inert tissues include, ligaments, skin, cartilage, capsules, fascia, dura mater and nerve roots

• Contractile tissue involves muscles and parts of including tendons

Skin Injuries

• Break in the continuity of skin as a result of trauma

• Anatomical Considerations– Skin (external covering) or integument represents

the largest organ of the bogy and consists of 2 layers• Epidermis• Dermis ( corium)

– Soft pliable nature of skin makes it easy to traumatize

• Injurious Mechanical Forces– Include friction, scraping, compression, tearing, cutting and penetrating

• Wound Classifications– Friction blister

• continuous rubbing over skin surface that causes a collection of fluid below or within epidermal layer

– Abrasion• Skin is scraped against rough surface resulting in capillary exposure due to skin

removal

– Skin Bruise (contusion)• Compression or crush injury of skin surface that produces bleeding under the

skin

– Laceration• Wound in which skin has been irregularly torn

– Skin Avulsion• Skin that is torn by same mechanism as laceration to

the extent that tissue is completely ripped from source

– Incision• Wound in which skin has been sharply cut

– Puncture• Penetration of the skin by a sharp object

Skeletal Muscle Injuries

• High incidence in athletics• Anatomical Characteristics

– Composed of contractile cells that produce movement

– Possess following characteristics• Irritability

• Contractility

• Conductivity

• Elasticity

– Three types of muscle• Cardiac• Smooth• Striated

Skeletal Muscle

Acute Muscle Injuries

• Contusions– Result of sudden blow to body– Can be both deep and superficial– Hematoma results from blood and lymph flow

into surrounding tissue• Localization of extravasated blood into clot,

encapsulated by connective tissue

• Speed of healing dependent on the extent of damage

– Can penetrate to skeletal structures causing a bone bruise– Usually rated by the extent to which muscle is able to

produce range of motion

• Strains– Stretch, tear or rip to muscle or adjacent tissue– Cause is often obscure

• Abnormal muscle contraction (result of 1)failure in reciprocal coordination of agonist and antagonist, 2) electrolyte imbalance due to profuse sweating or 3) strength imbalance

– May range from minute separation of connective tissue to complete tendinous avulsion or muscle rupture

– Muscle Strain Grades• Grade I - some fibers have been stretched or actually torn

resulting in tenderness and pain on active ROM, movement painful but full range present

• Grade II - number of fibers have been torn and active contraction is painful, usually a depression or divot is palpable, some swelling and discoloration result

• Grade III- Complete rupture of muscle or musculotendinous junction, significant impairment, with initially a great deal of pain that diminishes due to nerve damage

– Pathologically, strain is very similar to contusion or sprain with capillary or blood vessel hemorrhage

• Tendon Injuries– Wavy parallel collagenous fibers organized in bundles -

upon loading (up to 8,700- 18,000 lbs) collagen straightens but will return to shape after loading

– Breaking point occurs at 6-8% of increased length– Tears generally occur in muscle and not tendon– Repetitive stress on tendon will result in microtrauma

and elongation, causing fibroblasts influx and increased collagen production

• May evolve into chronic muscle condition , weakening tendons

• Muscle Cramps and Spasms– Painful involuntary contraction

– Attributed to dehydration/electrolyte imbalance

– Reflex reaction caused by trauma

– Two types• Clonic - alternating involuntary muscular contractions

and relaxations in quick succession

• Tonic - rigid contraction that lasts a period of time

– May lead to muscle or tendon injuries

Overexertional Muscle Problems

• Reflective in muscle soreness, decreased joint flexibility, general fatigue (24 hours post activity)

• Muscle Soreness– Overexertion in strenuous exercise resulting in

muscular pain– Generally occurs following participation in

activity that individual is unaccustomed

– Two types of soreness• Acute-onset muscle soreness - accompanies fatigue, and is

transient muscle pain experienced immediately after exercise• Delayed-onset muscle soreness (DOMS) - pain that occurs

24-48 hours following activity that gradually subsides (pain free 3-4 days later)

– Potentially caused by slight microtrauma to muscle or connective tissue structures

– Prevent soreness through gradual build-up of intensity

– Treat with static or PNF stretching and ice application within 48-72 hours of insult

• Muscle Stiffness– Does not produce pain– Result of extended period of work– Fluid accumulation in muscles, with slow reabsorbtion back into

bloodstream, resulting in swollen, shorter, thicker muscles --resistant to stretching.

– Light activity, motion, massage and passive mobilization assists in reducing stiffness

• Muscle Cramps– Related to hard conditioning– Tonic - result of electrolyte imbalance or interruption of muscle synergism– Clonic - stems from nerve irritation

• Muscle Guarding– Following injury, muscles within an effected

area contract to splint the area in an effort to minimize pain through limitation of motion

– Involuntary muscle contraction in response to pain following injury

• Not spasm which would indicate increased tone due to upper motor neuron lesion in the brain

Myofascial Trigger Points• Area of tenderness in a tight band of muscle

• Develop as the result of mechanical stress– Either acute strain or static postural positions producing

constant tension in muscle

• Typically occur in neck, upper and lower back

• Pain with palpation, with predictable pattern of referred pain which may also limit motion

• Pain may increase with active and passive motion of involved muscle

Chronic Musculoskeletal Injuries

• Progress slowly over long period of time

• Repetitive acute injuries can lead to chronic condition

• Constant irritation due to poor mechanics and stress will cause injury to become chronic

• Myositis/fascitis– Inflammation of muscle tissue– Fibrositis or inflammation of connective tissue– Plantar fascitis

• Tendinitis– Gradual onset, with diffuse tenderness due to repeated microtrauma and

degenerative changes– Obvious signs of swelling and pain

• Tenosynovitis– Inflammation of synovial sheath– In acute case - rapid onset, crepitus, and diffuse swelling– Chronic cases result in thickening of tendon with pain and crepitus

• Ectopic Calcification (myositis ossificans)– Striated muscle becomes chronically inflamed

resulting in myositis

– Can result in muscle that lies directly above bone

– Osteoid material accumulates rapidly and will either resolve in 9-12 months or mature with repeated trauma

– With maturation, surgery is required for removal

– Common sites, quadriceps and brachial muscle

• Atrophy and Contracture– Atrophy is wasting away of muscle due to

immobilization, inactivity, or loss of nerve functioning

– Contracture is and abnormal shortening of muscle where there is a great deal of resistance to passive stretch

• Generally the result of a muscle injury which impacts the joint, resulting in accumulation of scar tissue

Synovial Joints• Anatomical Characteristics

– Consist of cartilage and fibrous connective tissue– Joints are classified as

• Synarthrotic - immovable• Amphiarthrotic - slightly moveable• Diarthrotic - freely moveable (synovial articulations)

– Synovial Joint characteristics• Capsule or ligaments• Capsule is lined with synovial membrane• Hyaline cartilage• Joint cavity with synovial fluid• Blood and nerve supply with muscles crossing joint

• Joint Capsule– Bones are held together by a fibrous cuff– Consists of bundles of collagen and function to

maintain relative joint position– Extremely strong and can withstand cross

sectional forces– Will be slack or taut depending on joint

movement

• Ligaments– Sheets or bundles of collagen that form connection between

two bones

– Both intrinsic (inside the capsule) and extrinsic (outside the capsule)

– Similar composition to tendons

– Strong in the middle, weak at the ends

– When placed under undo stress may result in avulsion injury

– Viscoelastic properties are primary factor in ligamentous injuries

– Constant compression or tension causes ligament deterioration while intermittent stress strengthens

– Repeated microtrauma overtime makes capsule and ligaments more susceptible to major acute injuries

– Act as protective backup for joint• Primary protection is dynamic action of muscle

– Under fast loading conditions, ligament will fail, however, they provide maximal protection during rapid movements

– Will adapt based on Roux’s law of functional adaptation (organ will adapt structurally to alteration qualitative or quantitative of function)

• Synovial Membrane– Lines articular capsule– Single layer of flattened cells and villi– Secretes and absorbs fluid - serves as lubricant– Fluid contains hyaluronic acid (changes viscosity)

• Fast movement - thins fluid

• Slow movement - fluid thickens

• Articular Cartilage– Provides firm flexible support - semifirm connective tissue with

primarily ground substance– No direct blood or nerve supply

– Fibrocartilage: makes up vertebral disks, symphysis pubis and menisci

– Elastic: external ear and eustachian tubes– Hyaline: composes nasal septum, larynx, trachea, bronchi,

and articular ends of bone• Covers ends of bones in diarthrodial joints which serves as cushion

and sponge

• Can undergo compression and return to normal shape

• Degeneration producing microtrauma can occur following abnormal compressive forces

• Receives nourishment from synovium

• Provides motion control, stability and load transmission

• Additional Synovial Joint Structures– Fat

• Pads located in elbow, knee, to fill spaces between bones that form joints (lie between synovial membrane and the capsule)

– Articular Disks• Additional fibrocartilanginous disks

• Vary in shape and size and connected to capsule

• Exist in joints that operate in 2 planes of motions

• Aid in dispersion of synovial fluid

• Meniscus

• Nerve Supply– Capsule, ligaments, outer aspects of synovial

membrane and fat pads are well supplied– Inner structures (synovial membrane, cartilage

and articular cartilage) also supplied– Myelinated mechanoreceptors provide joint

position sense in fibrous capsule– Non-myelinated fibers supply blood vessels and

pain receptors

• Types of Synovial Joints– 6 types

• ball and socket - allows movement in all plane (hip)

• hinge - allows for flexion and extension (elbow)

• pivot - rotation about and axis (cervical atlas and axis)

• ellipsoidal - elliptical convex and concave articulation (wrist)

• saddle - reciprocally convex-concave (carpometacarpal joint of thumb)

• gliding - all sliding back and forth (carpal joints)

• hinge, pivot, ellipsoidal, saddle, and gliding

• Functional Synovial Joints– Differ in their ability to withstand trauma depending on

skeletal, ligamentous, and muscular organization– Synovial Joint Stabilization

• Muscle tension helps to limit synovial joint movement• With stretching of the capsule, muscle reflex contractions prevent

overstretching• Nerve supply is governed by Hilton’s Law (capsule, skin and

muscle have same nerve supply)• Ligaments can extend due to right angle structural design but are

not elastic

• Joint structure vs. ligament contribution to joint stability• Muscles absorb forces involved in load transmission and

may provide dynamic stabilizing through integration into joint capsule and by crossing joints

– Articular Capsule and Ligaments• Help maintain anatomical integrity and structural alignment

of joints• Ligaments have spiral arrangement of collagenous tissue• Ligaments tend to be stronger in the middle and weak at the

ends• Respond quicker than muscle to over-stretching

• Synovial Joint Trauma– Major factor in injury is viscoelastic properties of ligaments and capsule– While constant compression is damaging, periodic tension increases

overall strength of tissue– Subject to same mechanical forces that cause injury

• Synovial Joint Injury Classifications– Acute Joint Injuries– Sprains

• Result of traumatic joint twist that causes stretching or tearing of connective tissue

• Graded based on the severity of injury

• Grade I - some pain, minimal loss of function, no abnormal motion, and mild point tenderness

• Grade II - pain, moderate loss of function, swelling, and instability

• Grade III - extremely painful, inevitable loss of function, severe instability and swelling, and may also represent subluxation

• Can result in joint effusion and swelling, local temperature increase, pain and point tenderness, ecchymosis (change in skin color) and possibly an avulsion fracture

• Most vulnerable joints include ankles, knees, and shoulders

• Sometimes difficult to distinguish between sprain and tendon strain

• Repeated joint twisting could result in arthritis or chronic inflammation

– Acute Synovitis• Synovial membrane can be acutely injured via contusion or strain• Irritation of membrane results in increased fluid production and swelling

occurs• Results in joint pain along with skin sensitivity• With proper treatment, effusion and pain will diminish

– Subluxations, Dislocations and Diastasis• High level of incidence in fingers and shoulder • Subluxations are partial dislocations causing incomplete separation of two

bones• Luxation presents with total disunion of bone apposition between articular

surfaces• Diastisis is the disjointing of 2 parallel bones or rupture of a solid joint

(symphysis pubis)

• Factors associated with dislocations - 1) loss of limb function, 2) gross deformity, 3)swelling and point tenderness

• X-ray is the only absolute diagnostic technique (able to see bone fragments from possible avulsion fractures, disruption of growth plates or connective tissue

• Dislocations (particularly first time) should always be considered and treated as a fracture until ruled out

• “Once a dislocation, always a dislocation”

• Chronic Joint Injuries– Stem from microtrauma and overuse

– Include, osteochondrosis, osteoarthritis, and in adolescence epiphyseal injuries

– Major cause involves failure of muscle to control or limit deceleration

– To prevent, a combination of chronic fatigue and training should be avoided, and protective gear should be used to enhance absorption of impact forces

– Osteochondrosis • Also known as osteochrondritis dissecans and apophysitis (if

located at a tubercle/tuberosity)

• Causes not well understood

• Degenerative changes to epiphyses of bone during rapid child growth

• Possible cause includes 1)aseptic necrosis (disrupted circulation to epiphysis, 2) fractures in cartilage causing fissures to subchondral bone, 3) trauma to a joint that results in cartilage fragmentation resulting in swelling, pain and locking

• With the apophysis, an avulsion fracture may be involved, including pain, swelling and disability

– Osteoarthritis• Wearing away of hyaline cartilage as a result of normal use• Changes in joint mechanics lead joint degeneration (the result of

repeated trauma to tissue involved)• May be the result of direct blow, pressure of carrying and lifting

heavy loads, or repeated trauma from an activity such as running or cycling

• Commonly affects weight bearing joints but can also impact shoulders and cervical spine

• Symptoms include pain (as the result of friction), stiffness, prominent uprising in the morning, localized tenderness, creaking, grating, and often is localized to one side of the joint or generalized joint pain

– Bursitis• Fluid filled sac that develops in area of friction

• Sudden irritation can cause acute bursitis, while overuse and constant external compression can cause chronic bursitis

• Signs and symptoms include swelling, pain, and some loss of function

• Repeated trauma can lead to calcification and degeneration of internal bursa linings

– Capsulitis and Synovitis• Capsulitis is the result of repeated joint trauma

• Synovitis can occur acutely but will also develop following mistreatment of joint injury

• Chronic synovitis can result in edema, thickening of the synovial lining, exudation can occur and a fibrous underlying develops --motion may be restricted and joint noises may occur

Skeletal Trauma

• Anatomical Characteristics– Dense connective

tissue matrix

– Outer compact tissue

– Inner porous cancellous bone including Haversian canals

– Bone Functions• Body support

• Organ protection

• Movement (through joints and levers)

• Calcium storage

• Formation of blood cells (hematopoiesis)

– Types of Bone• Classified according to shape

• Flat bones - skull, ribs, scapulae

• Irregular bones - vertebrae and skull

• Short bones- wrist and ankle

• Long bones - humerus, ulna, tibia, radius, fibula, femur

- bones most commonly injured

– Gross Structures• Diaphysis -shaft - hollow and cylindrical

- covered by compact bone)

- medullary cavity contains yellow

marrow• Epiphysis - composed of cancellous bone and

has hyaline cartilage covering

- provides areas for muscle attachment• Periosteum - dense, white fibrous covering which

penetrates bone via Sharpey’ fibers• - contains blood vessels and osteoblasts

– Microscopic Structures• Calcium salts impregnate intracellular bone substance (makes bone hard)• Osteocytes located in hollow spaces are called lacunae• Haversian systems are the structural units of bone• Compact bone has interspersed lamellae to fill spaces between canals• Cancellous bone has numerous open spaces between thin processes of

trabeculae • Trabeculae serve as scaffolding and align along points of stress within the

bone to add structural strength• Blood circulation connects perisosteum with haversian canals through

Volkmann’s canal• Medullary cavity and bone marrow are supplied directly by one or more

arteries

– Bone Growth• Ossification occurs from synthesis of bones organic matrix (work of

osteoblasts and osteoclasts)• Involves the epiphyseal growth plates located at the ends of long

bones• As cartilage matures, immature osteoblasts replace to ultimately

form bone• Deforming forces, premature injury and growth plate dislocation

can alter growth patterns and/or result in deformity of bone• Bone diameter increases via the activity of osteoblasts adding to the

exterior while osteoclasts break down bone in medullary cavity• At full size, bone maintains state of balance between osteoblastic

and -clastic activity

• Changes in activity and hormonal levels can alter balance

• Bone loss begins to exceed external bone growth overtime

• As thickness decreases, bones are less resistant to forces --osteoporosis

• Bone’s functional adaptation to stresses follow’s Wolff’s Law --every change in form and function or in its function alone is followed by changes in architectural design

• Bone Injuries– While have viscoelastic properties, bone is fairly rigid and

serves as a poor shock absorber– Brittle nature increases under tension rather than compression– Cylindrical nature of bones make them very strong - resistant

to bending and twisting

– Anatomical Weak Points• Stresses become concentrated in areas where changes in shape and

direction occur• Gradual changes in shape are much more advantageous

– Load Characteristics• Bones can be stressed or loaded to fail by tension,

compression, bending, twisting and shearing

• Either occur singularly or in combination

• Amount of load also impact the nature of the fracture

• More force results in a more complex fracture

• While force goes into fracturing the bone, energy and force is also absorbed by adjacent soft tissues

• Some bones will require more force than others

• Bone’s magnitude of stress and strain in most prevalent at it outer surface and decreases to zero at its center

– Bone Trauma Classifications• Periostitis - inflammation of the periosteum, result primarily of

contusions and produces rigid skin overlying muscle (acute and chronic)

• Acute bone fractures - partial or complete disruption that can be either closed or open (through skin); serious musculoskeletal condition

• Type of fractures include, depressed, greenstick, impacted, longitudinal, oblique, serrated, spiral, transverse, comminuted, blowout, and avulsion

• Stress fractures- no specific cause but with a number of possible causes

– Overload due to muscle contraction, altered stress distribution due to muscle fatigue, changes in surface, rhythmic repetitive stress vibrations

• Bone becomes susceptible early in training due to increased muscular forces and initial remodeling and resorption of bone

• Progression involves, focal microfractures, periosteal or endosteal response (stress fx) linear fractures and displaced fractures

• Typical causes include– Coming back to competition too soon after injury

– Changing events without proper conditioning– Starting initial training too quickly– Changing training habits (surfaces, shoes….etc)– Variety of postural and foot conditions

• Early detection is difficult, bone scan is useful, x-ray is effective after several weeks

• Major signs and symptoms include focal tenderness and pain, (early stages) pain with activity, (later stages) pain becomes constant and more intense, particularly at night, positive percussion tap test

• Common sites involve tibia, fibula, metatarsal shaft, calcaneus, femur, pars interarticularis, ribs, and humerus

• Management varies between individuals, injury site and extent of injury

• More easily managed and healed if on compression side of bone vs. tension (may result in complete fx)

• Epiphyseal Conditions - three types can be sustained by adolescents (injury to growth plate, articular epiphysis, and apophyseal injuries)

– Occur most often in children ages 10-16 yrs. Old

• Classified by Salter-Harris into five types (see photo on next slide)

• Apophyseal Injuries - Young physically active individuals are susceptible

– Apophyses are traction epiphyses in contrast to pressure epiphyses.– Serve as sites of origin and insertion for muscles– Common avulsion conditions include Sever’s disease and Osgood-

Schlatter’s disease

Nerve Trauma

• Abnormal nerve responses can be attributed to injury or athletic participation

• The most frequent injury is neuropraxia produced by direct trauma

• Lacerations of nerves as well as compression of nerves as a result of fractures and dislocations can impact nerve function

• Anatomical Characteristics– Provides sensitivity and communication from the CNS to

muscles, sense organs and various systems in the periphery– Neuron cell body has a large nucleus with branched

dendrites which respond to neurotransmitter substances– Each nerve cell has an axon that conducts nerve impulse– Axons are encased in neurilemmal sheaths (Schwann and

satellite cells)– Various neurological cells in CNS help to form framework

for nervous tissue

• Nerve Injuries– Two main causes of injury - compression and tension– May be acute or chronic– Physical trauma causes pain and can result in a host

of sensory responses (pinch, burn, tingle, muscle weakness, radiating pain)

– Long term problems (neuritis) can go from minor nerve problems to paralysis

– Pain can be referred as well

Body Mechanics

• Body move very effectively in upright position - able to overcome great forces even with inefficient lever system

• Body must overcome inertia, muscle viscosity and unfavorable angles of pull

• Mechanical reasons for injury - hereditary, congenital, or acquired defects may predispose athlete to injury

• Body build, structural make-up, habitual incorrect application of skill may also predispose individual to injury

• Microtrauma and Overuse Syndrome– Injuries as a result of abnormal and repetitive stress and

microtraumas fall into a class with certain identifiable syndromes– Frequently result in limitation or curtailment of sports

involvement– Often seen in running, jumping, and throwing activities– Some of these injuries while small can be debilitating – Repetitive overuse and stress injuries include

• Achilles tendinitis, shin splints, stress fx, Osgood-Schlater’s disease, runner’s and jumper’s knee, patellar chondromalacia and apophyseal avulsion

• Postural Deviations– Often an underlying cause of injury– May cause unilateral muscle use as well as bony and soft tissue

asymmetries– Results in poor pathomechanics– Imbalance is manifested by postural deviations as body tries to regain

balance relative to CoG– Injury generally becomes chronic and participation must stop– Athletic trainer should attempt to correct postural conditions– Postural conditions can make athletes exceedingly more prone to

injury–