Chapter 5 - Mechanisms of Injury Physical process responsible for a given action, reaction or result

Why is it necessary to determine the mechanism of injuries?Important for the diagnosis, rehabilitation and prevention of injuries

Injury MechanismDepends persons perspectiveMechanism often acts in combinationEstablish cause and effect relationshipSport medicine classificationContact or impactdynamic overloadoverusestructural vulnerabilityinflexibilitymuscle inbalancerapid growth

Mechanical LoadingLoads greater than physiological lead to injuriesChronic injuriescumulative traumarepetitive stressAcute injuries

Principles of InjuriesCatch-all termsshinsplintstennis elbowjumpers kneeLevel of dysfunctioncatastrophic injuriesProgressionuntreated or lack to time to heal lead to more severe injuries

Assessment of SeverityClinical classificationshelp assign common characteristics to injuriesSeverity linked to amount of tissue damageMild & moderate: partial disruption, tissue is able to accept loads

Ligamentsgrade 1 mildnegligible structuralminimal time lossgrade 2 moderatepartial ruptureswelling tendernessup to 6 wk timegrade 3 severecomplete, gross swelling, 8 wk min

Injury PrinciplesMicro vs macrotraumaPrimary: direct consequence of traumaSecondaryinjury surface after original traumaaccommodation to primary injury (adaptation of loads)Tissue structure

Contributing factorsAgeacute injuries: youngchronic: olderGenderGeneticsFitness levelNutritionPsychologicalHuman interactionFatiguephysical & mentalEnvironment

Equipmentprotectivecontributes to injuriesPrevious injuryDiseaseDrugsRehabilitationAnthropometricsSkill levelExperiencePain

Tissue InjuryInflammation: pathological processvascular responseincrease capillary permeability (swelling)Pain: swelling related pressure on nerve endings (more in confined spaces)

Tissue InjuryVasodilatory phaseflow of fluid/plasma proteins into tissuePlasma proteinsfibrinogenFunctionsdilutes & inactivates toxinsnutrients to inflammatory cellsantibodies, proteins

Control of inflammationChemicals mediatorshistamine, serotonin, bradykin, prostagladins, plasmin etc.Other CellsPhagocytes (fungal and bacterial infection)Lymphocytes (antigens)

Why inflammation?Bodys first line of defense against injuries

BoneAny conditions that affects osteocyte performanceOsteonecrosis: cessation of blood flowvessel disruptionocclussioninjury or pressure to arterial walls matrix, bone strength likelihood of fracture

BoneOsteoporosisMajor public health issueAffect mostly trabercular boneBone of axial skeletonMultifactorClinical conditions

BoneFracture (break): applied loads exceeds bones ability Resistancematerial propertiesgeometryanisotropic effectsporosityType of loadingacute vs chronic

FracturesIndirect or directRisk and type of boneDiagnosissiteextent of injuryconfigurationfragments (displaced)environmental (open closed)complicationsetiological

FracturesHealing phases:inflammationunion of bony ends (3wk)callus remodeling (6 wks)

Articular CartilageExcessive loadingloss of cartilage matrixchondral fracturesosteochondral fractureInability to repair

Articular CartilageAOnon inflammatoryweight bearing jointsdeterioration of ACosteophytes formationcartilage fibrillationArtificial Jointscemented or non

FibrocartilageDistributes forces at jointsShock absorberImprove joint fitmenisciintervertebral disks

TendonForce transferInjuriesdirect (cuts)indirect (excessive loads applied to unit)Musculotendinous injuries: StrainMild, moderate, severesevere: precede by microdamage

TendonRepetitive overloading: inflammatory response or tendinitisAlso could affect tendon sheath, peritenon etc.HealingInflammationSynthesis of collagen and GAG (matrix)Cyclic loading (2-3 wk)Progressive stress

PeritenonitisTendinosis (intratendinous degeneration dut ot atrophy)Tendinitis (Symptomatic degeneration vascular disruption and inflammation

LigamentsLigament injuriessprainpartial tearscomplete tearsHealingbleeding & inflammation (fibrin, fibroblas scar cells)proliferation of building material (scar tissue)matrix remodeling smaller fiberslack organization

Muscle InjuriesAcute muscular strainoverstreching or overloadingforce, rate, applicationmoderate:partial tearsevere: complete tear, hemorrage, swellingcontusionsintramuscular bleedingmyositis ossificansexercise induced injuryDOMS 24-72 hr after exerciseeccentric

SkinAbrasionsContusionsPenetrating woundsobscure deeper damageLacerationsInfectionExcessive bleeding

Nervous tissueNot musculoskeletalGreatest potential for dysfunctionInjurieschemicalthermalischemicmechanicalentrapment trauma: compressive or tensileTemporary or complete axonal discontinuityMotor impairment can lead to secondary injuries

Nervous Tissue

Degree

Mechanism

Effect

First degree

Low compression or acute high compression

Conduction block, no axonal discontinuity

Second degree

Pinching or crunching

Prolonged pressure

Axonal interruption, wallerian degeneration, nerve supporting structure intact (recovery ok)

Third degree

Any of the above

Loss of continuity, damage to axons and sheath, loss of sensory and motor. Slow recovery

Fourth degree

Loss of all tissue except epineurial tissue, surgical repair

Fifth degree

Severance of nerve trunk

Incomplete regeneration, if occurs, needs surgical repair

Nervous TissueCompartment or entrapments of nerves or vesselsIncrease pressure transmittedEnclosed spacingSymptonsnumbness, tingling & paindecreased vessel perfusionInflammation: positive feedback loop

Joint InjuriesExcessive loadingDislocation (luxation)Partial dislocation (subluxation)SynovitisArthritisOARAGouty