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2008 Annual Conference Injury Biomechanics (How People Get Hurt) Anastasios “Tassos” Tsoumanis, Ph.D. Principal Consultant Objectives • • • • • • Basics of tissue biomechanics Basics of injury causation Injury biomechanics Situations & their injury potential Reading medical reports regarding injuries Warning! Graphic images... Anatomic Orientation Terms • Anterior: Forward • Posterior: Rear • Medial: Towards the middle • Lateral: Towards the side • Proximal: Close to the head • Distal: Further from the head Tissue Biomechanics • • • • • Bone Ligament Tendon Muscle Other soft tissues Bone • Hard, mineralized tissue – Cortical – outside, hard – Medullary – inside, “spongy” Bone • Stronger along the lines where forces are naturally applied How Bones Fracture Femur Fractures Fracture Patterns • If you read “spiral fracture” – Think torsion • If you read “transverse fracture” – Think bending • If you read “oblique fracture” – Think axial force • If you read “comminuted” – Think high energy/velocity Ligaments • Tough rope-like connective tissue between 2 bones Ligaments Can tear in the middle (midsubstance tear) – Partial or complete Can pull off from a bone (avulsion) Muscles • Contractile • Made up of sliding fibers • Create greatest force when forcefully stretched while contracting Muscles • Most tears happen when contracts but is still being lengthened • Most tears happen at the junction between muscle and tendon Tendons • Connect muscle to bone • Structure similar to ligaments Tendons • Can tear – Partial or complete Tendons • Can tear – Partial or complete • Can avulse • Takes great force to tear or avulse normal tendon • Happens when its muscle lengthens against a contraction Joint Capsules • Soft tissues surrounding joints • Thinner than ligaments • Contain joint fluid within the joint • Tear with dislocations Soft Tissue Injuries • Muscle – Strain – Tear – Rupture • Most often, muscle tears occur at junction between muscle and tendon • Ligament – – – – Sprain Partial Tear Complete Tear Joint Dislocation Anatomy And Injury Biomechanics • • • • • Skeletal System Anatomy Upper Extremity Lower Extremity Spine Head Wrist • Radius, Ulna, Carpal bones • Ligaments • Tendons • Carpal Tunnel Wrist Injuries • Carpal Tunnel Syndrome “cumulative trauma disorder” • Sprains • Fractures Elbow Elbow Injuries • Tennis Elbow (overuse) • Golfer’s Elbow (overuse) Shoulder Anatomy • • • • • • Ball and Socket joint Head of Humerus (ball) Glenoid (socket) Scapula Acromion Clavicle Anterior Shoulder Dislocation • P-A force on shoulder or humerus Anterior Shoulder Dislocation • Head of humerus comes forward (anterior) out of the socket Posterior Shoulder Dislocation • Fairly uncommon (5%) • A-P force on shoulder or humerus • Seizures • Electrocution AC Joint Separation • Downwards force on shoulder • Separates clavicle and rest of shoulder • Falls Rotator Cuff Tear • Muscles that rotate the upper arm • Injuries are to the tendons, not muscle fibers • Overuse or violent humerus external rotation • Depends on position (abduction) Functional Knee Anatomy • Femur, Tibia, Patella • Anterior and Posterior Cruciate Ligaments • Medial and Lateral Colateral Ligaments • Meniscus ACL • ACL prevents the tibia from moving forward on the femur and from rotating inwards • Cutting • Hyperextension Posterior Cruciate Ligament Posterior Cruciate Ligament Collateral Ligaments • Can be injured when a force tries bend the knee in a lateral direction • The ligament getting stretched is the one that gets injured Ankle Sprain Anatomy of the Spinal Column • • • • Segment Curvatures Segment Mobilities Vertebral Body Sizes Atlanto-Axial Joint Intervertebral Disc • Viscoelastic (like silly putty) • On high speed impacts, vertebral fractures are more likely than disc ruptures! • The only way to “pop a disc” on a single event is combined compression and bending (torsion helps) Disc Problems Spinal Column Injuries • Injury pattern depends on mechanics • Danger of injuring spinal cord Skull Anatomy Facial Bone Impact Tolerance Brain Injury • Concussion – No structural damage, but some temporary loss of function • Contusion – More serious, bruising of the brain • Countercoup – brain injury on the opposite side of where contact occurs Brain Bleeds • Sub or epi-dural hematomas -contact • Sub-arachnoid or intracranial hemorrhage - acceleration Temporo Mandibular Joint (TMJ) • One of the most highly stressed joints in the body • Direct impact to the jaw or joint • TMJ syndrome – chronic! Considerations • Mechanism of injury • Loads sustained by tissue • Tissue tolerance to loads – Pre existing conditions (tissue attenuation) Biomechanics Approach I. Assessment of Situation Mechanics – What Happened? • • • • II. Witness statements Site inspection (regulations, standards, laws) Other information (incident reports) Modeling Review of Medical Records – What is hurt? • • III. Determination of claimed injuries Pre-existing conditions Analysis – Do I and II make sense? • • • Correlation between claimed injuries and event mechanics Differentiate acute and chronic conditions Assess effect of pre-existing conditions Injury Claim Scenarios True? False? Rotator Cuff Tear • “Airbag blew up and flung my arm back and out” • “Bus hit a pothole and steering wheel jerked left” √ X Anterior Shoulder Dislocation • “Fell back onto my outstretched hand” • “In the accident (sideswipe)” √ X Disc Herniation • Dx: Lumbar disc herniation with osteophytes • “Years of heavy √ labor” • “In the accident (low speed rear end collision)” X TMJ Injury • “In the accident (low speed rear end collision)” X • “Airbag blew up and hit me in the jaw” √ Fatal Injuries • 26 y/o woman sustained fatal slip and fall injury in bathroom • Cause of death: brain hemorrhage due to head hitting toilet rim • Reported injuries: 2 scalp lacerations, contusion on right side of neck, anterior iliac spines • Non-reported injuries (evident photographically) – Abrasions on left side of neck (3), chin, both shoulders – Cut lip – 2 parallel linear marks on back • Accidental slip and fall? X Thank You