Annual Conference 2008

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

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? Witness statements Site inspection (regulations, standards, laws) Other information (incident reports) Modeling II.Review of Medical Records – What is hurt? Determination of claimed injuries Pre-existing conditions III.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 “Years of heavy labor” “In the accident (low speed rear end collision)” X √ Dx: Lumbar disc herniation with osteophytes

TMJ Injury “In the accident (low speed rear end collision)” “Airbag blew up and hit me in the jaw” X √

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