Chapter 5 - Mechanisms of Chapter 5 - Mechanisms of Injury Injury

Physical process responsible Physical process responsible for a given action, reaction or for a given action, reaction or

resultresult

Why is it necessary to Why is it necessary to determine the mechanism of determine the mechanism of

injuries?injuries?

Important for the diagnosis, Important for the diagnosis, rehabilitation and prevention rehabilitation and prevention

of injuriesof injuries

Injury MechanismInjury Mechanism

Depends persons Depends persons perspectiveperspective

Mechanism often Mechanism often acts in acts in combinationcombination

Establish cause Establish cause and effect and effect relationshiprelationship

Sport medicine Sport medicine classificationclassification– Contact or impactContact or impact– dynamic overloaddynamic overload– overuseoveruse– structural structural

vulnerabilityvulnerability– inflexibilityinflexibility– muscle inbalancemuscle inbalance– rapid growthrapid growth

Mechanical LoadingMechanical Loading

Loads greater Loads greater than physiological than physiological lead to injurieslead to injuries

Chronic injuriesChronic injuries– cumulative cumulative

traumatrauma– repetitive stressrepetitive stress

Acute injuriesAcute injuries

Principles of InjuriesPrinciples of Injuries

Catch-all termsCatch-all terms– shinsplintsshinsplints– tennis elbowtennis elbow– jumper’s kneejumper’s knee

Level of dysfunctionLevel of dysfunction– catastrophic injuriescatastrophic injuries

ProgressionProgression– untreated or lack to time to heal lead to untreated or lack to time to heal lead to

more severe injuries more severe injuries

Assessment of SeverityAssessment of Severity Clinical classificationsClinical classifications

– help assign common help assign common characteristics to characteristics to injuriesinjuries

Severity linked to Severity linked to amount of tissue amount of tissue damagedamage

Mild & moderate: Mild & moderate: partial disruption, partial disruption, tissue is able to accept tissue is able to accept loadsloads

LigamentsLigaments– grade 1 mildgrade 1 mild

negligible structuralnegligible structural minimal time lossminimal time loss

– grade 2 moderategrade 2 moderate partial rupturepartial rupture swelling tendernessswelling tenderness up to 6 wk timeup to 6 wk time

– grade 3 severegrade 3 severe complete, gross complete, gross

swelling, 8 wk minswelling, 8 wk min

Injury PrinciplesInjury Principles Micro vs macrotraumaMicro vs macrotrauma Primary: direct Primary: direct

consequence of consequence of traumatrauma

SecondarySecondary– injury surface after injury surface after

original traumaoriginal trauma– accommodation to accommodation to

primary injury primary injury (adaptation of loads)(adaptation of loads)

Tissue structureTissue structure

Contributing factorsContributing factors AgeAge

– acute injuries: youngacute injuries: young– chronic: olderchronic: older

GenderGender GeneticsGenetics Fitness levelFitness level NutritionNutrition PsychologicalPsychological Human interactionHuman interaction FatigueFatigue

– physical & mentalphysical & mental EnvironmentEnvironment

EquipmentEquipment– protectiveprotective– contributes to injuriescontributes to injuries

Previous injuryPrevious injury DiseaseDisease DrugsDrugs RehabilitationRehabilitation AnthropometricsAnthropometrics Skill levelSkill level ExperienceExperience PainPain

Tissue InjuryTissue Injury

Inflammation: Inflammation: pathological processpathological process– vascular responsevascular response– increase capillary increase capillary

permeability permeability (swelling)(swelling)

Pain: swelling related Pain: swelling related pressure on nerve pressure on nerve endings (more in endings (more in confined spaces)confined spaces)

Tissue InjuryTissue Injury

Vasodilatory phaseVasodilatory phase– flow of fluid/plasma flow of fluid/plasma

proteins into tissueproteins into tissue Plasma proteinsPlasma proteins

– fibrinogenfibrinogen FunctionsFunctions

– dilutes & inactivates dilutes & inactivates toxinstoxins

– nutrients to nutrients to inflammatory cellsinflammatory cells

– antibodies, proteinsantibodies, proteins

Control of inflammationControl of inflammation– Chemicals mediatorsChemicals mediators

histamine, serotonin, histamine, serotonin, bradykin, bradykin, prostagladins, plasmin prostagladins, plasmin etc.etc.

– Other CellsOther Cells Phagocytes (fungal Phagocytes (fungal

and bacterial and bacterial infection)infection)

Lymphocytes Lymphocytes (antigens)(antigens)

Why inflammation?Why inflammation?

Body’s first line of defense Body’s first line of defense against injuriesagainst injuries

BoneBone Any conditions that Any conditions that

affects osteocyte affects osteocyte performanceperformance

Osteonecrosis: Osteonecrosis: cessation of blood flowcessation of blood flow– vessel disruptionvessel disruption– occlussionocclussion– injury or pressure to injury or pressure to

arterial wallsarterial walls matrix, bone strengthmatrix, bone strength likelihood of fracturelikelihood of fracture

BoneBone

OsteoporosisOsteoporosis Major public health Major public health

issueissue Affect mostly Affect mostly

trabercular bonetrabercular bone Bone of axial Bone of axial

skeletonskeleton MultifactorMultifactor Clinical conditionsClinical conditions

BoneBone

Fracture (break): Fracture (break): applied loads applied loads exceeds bone’s exceeds bone’s abilityability

ResistanceResistance– material propertiesmaterial properties– geometrygeometry– anisotropic effectsanisotropic effects– porosityporosity

Type of loadingType of loading– acute vs chronicacute vs chronic

FracturesFractures

Indirect or directIndirect or direct Risk and type of boneRisk and type of bone DiagnosisDiagnosis

– sitesite– extent of injuryextent of injury– configurationconfiguration– fragments (displaced)fragments (displaced)– environmental (open environmental (open

closed)closed)– complicationscomplications– etiologicaletiological

FracturesFractures

Healing phases:Healing phases:– inflammationinflammation– union of bony ends (3wk)union of bony ends (3wk)– callus remodeling (6 wks)callus remodeling (6 wks)

Articular CartilageArticular Cartilage

Excessive loadingExcessive loading– loss of cartilage loss of cartilage

matrixmatrix– chondral fractureschondral fractures– osteochondral osteochondral

fracturefracture Inability to repairInability to repair

Articular CartilageArticular Cartilage

AOAO– non inflammatorynon inflammatory– weight bearing weight bearing

jointsjoints– deterioration of ACdeterioration of AC– osteophytes osteophytes

formationformation– cartilage fibrillationcartilage fibrillation

Artificial JointsArtificial Joints– cemented or noncemented or non

FibrocartilageFibrocartilage

Distributes forces Distributes forces at jointsat joints

Shock absorberShock absorber Improve joint fitImprove joint fit meniscimenisci intervertebral intervertebral

disksdisks

TendonTendon Force transferForce transfer InjuriesInjuries

– direct (cuts)direct (cuts)– indirect (excessive loads indirect (excessive loads

applied to unit)applied to unit) Musculotendinous Musculotendinous

injuries: Straininjuries: Strain

– Mild, moderate, Mild, moderate, severesevere

– severe: precede severe: precede by microdamageby microdamage

TendonTendon Repetitive overloading: Repetitive overloading:

inflammatory response inflammatory response or tendinitisor tendinitis

Also could affect tendon Also could affect tendon sheath, peritenon etc.sheath, peritenon etc.

HealingHealing

– InflammationInflammation– Synthesis of collagen Synthesis of collagen

and GAG (matrixand GAG (matrix))– Cyclic loading (2-3 Cyclic loading (2-3

wk)wk)– Progressive stressProgressive stress

PeritenonitisPeritenonitis Tendinosis Tendinosis

(intratendinous (intratendinous degeneration dut ot degeneration dut ot atrophy)atrophy)

Tendinitis (Symptomatic Tendinitis (Symptomatic degeneration vascular degeneration vascular disruption and disruption and inflammationinflammation

LigamentsLigaments

Ligament injuriesLigament injuries– sprainsprain– partial tearspartial tears– complete tearscomplete tears

HealingHealing– bleeding & inflammation bleeding & inflammation

(fibrin, fibroblas scar cells)(fibrin, fibroblas scar cells)– proliferation of building proliferation of building

material (scar tissue)material (scar tissue)– matrix remodeling matrix remodeling

smaller fiberssmaller fibers lack organizationlack organization

Muscle Muscle InjuriesInjuries

– Acute muscular strainAcute muscular strain overstreching or overstreching or

overloadingoverloading force, rate, applicationforce, rate, application moderate:partial tearmoderate:partial tear severe: complete tear, severe: complete tear,

hemorrage, swellinghemorrage, swelling

– contusionscontusions intramuscular bleedingintramuscular bleeding myositis ossificansmyositis ossificans

– exercise induced injuryexercise induced injury DOMS 24-72 hr after DOMS 24-72 hr after

exerciseexercise eccentriceccentric

SkinSkin

AbrasionsAbrasions ContusionsContusions Penetrating woundsPenetrating wounds

– obscure deeper obscure deeper damagedamage

LacerationsLacerations InfectionInfection Excessive bleedingExcessive bleeding

Nervous tissueNervous tissue Not musculoskeletalNot musculoskeletal Greatest potential for Greatest potential for

dysfunctiondysfunction InjuriesInjuries

– chemicalchemical– thermalthermal– ischemicischemic– mechanicalmechanical

entrapment entrapment trauma: compressive trauma: compressive

or tensileor tensile

Temporary or complete Temporary or complete axonal discontinuityaxonal discontinuity

Motor impairment can Motor impairment can lead to secondary lead to secondary injuriesinjuries

Nervous TissueNervous TissueDegree Mechanism Effect

First degree Low compression or acutehigh compression

Conduction block, noaxonal discontinuity

Second degree Pinching or crunchingProlonged pressure

Axonal interruption,wallerian degeneration,nerve supporting structureintact (recovery ok)

Third degree Any of the above Loss of continuity, damageto axons and sheath, lossof sensory and motor.Slow recovery

Fourth degree Loss of all tissue exceptepineurial tissue, surgicalrepair

Fifth degree Severance of nerve trunk Incomplete regeneration, ifoccurs, needs surgicalrepair

Nervous TissueNervous Tissue Compartment or Compartment or

entrapments of nerves or entrapments of nerves or vesselsvessels– Increase pressure Increase pressure

transmittedtransmitted– Enclosed spacingEnclosed spacing

SymptonsSymptons– numbness, tingling & numbness, tingling &

painpain– decreased vessel decreased vessel

perfusionperfusion Inflammation: positive Inflammation: positive

feedback loopfeedback loop

Joint InjuriesJoint Injuries Excessive loadingExcessive loading Dislocation (luxation)Dislocation (luxation) Partial dislocation Partial dislocation

(subluxation)(subluxation) SynovitisSynovitis ArthritisArthritis

– OAOA– RARA– GoutyGouty