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2008
Annual Conference
Injury Biomechanics
(How People Get Hurt)
Anastasios “Tassos” Tsoumanis, Ph.D.
Principal Consultant
Objectives
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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
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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
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Sprain
Partial Tear
Complete Tear
Joint Dislocation
Anatomy And Injury Biomechanics
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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
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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
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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?
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II.
Witness statements
Site inspection (regulations, standards, laws)
Other information (incident reports)
Modeling
Review of Medical Records – What is hurt?
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III.
Determination of claimed injuries
Pre-existing conditions
Analysis – Do I and II make sense?
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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