Comprehensive Study Notes on Injury Biomechanics

Introduction to Injury Biomechanics

  • Key Competencies Post-Chapter Completion:

    • List the five forms of energy.

    • Describe the physical properties of kinetic energy.

    • Discuss the role of kinetic energy in producing injury.

    • Describe occupant kinematics for five types of motor vehicle collisions.

    • Discuss clinical implications of each type of collision.

    • Describe kinematics of motorcycle collisions and relevant clinical implications.

    • Discuss the six components of ballistics and their clinical implications.

    • List and describe four types of blast injuries and their clinical implications.

    • Define the role of injury biomechanics in the assessment of the trauma patient.

Assessment of Injury Patients

  • Comparison of trauma to medical patients includes:

    • Thorough scene assessment.

    • Physical examination.

    • Acquisition of past medical history and history of present illness.

    • Technical tools available for medical patients (e.g., EKG, rapid assays for troponin) are less available for trauma patients.

Importance of Scene Assessment:

  • Trauma assessment relies on:

    • Index of suspicion based on a thorough understanding of injury biomechanics.

    • Historical context of the trauma event (pre-event, event, post-event phases).

Phases of Trauma Events

Pre-Event Phase:

  • Information gathered to diagnose potential injuries (pre-existing conditions, drug/alcohol use).

  • Examples of critical data include:

    • Previous medical conditions (e.g., hemophilia) affecting injury response.

    • Bystander accounts of events leading to injuries (e.g., erratic driving behavior).

Event Phase:

  • The moment an injury occurs, focusing on:

    • Rapid deceleration of the vehicle upon impact while occupants remain in motion until they hit the interior.

    • Common types of impacts:

    • Knees into dashboard.

    • Chest into steering wheel.

    • Head into windshield.

  • Effects of kinetic energy transfer leading to physical injuries.

Post-Event Phase:

  • Analysis of physical evidence left at the scene to predict injuries (e.g., vehicle damage, windshield breakage).

  • Goal is to establish a thorough understanding of kinematics to treat visible and occult injuries.

Kinetic Energy and Injury

  • Definition of Kinetic Energy: KE=rac12mv2KE = rac{1}{2}mv^2

    • Where:

    • $m$ = mass of the object

    • $v$ = velocity of the object

  • Energy types that can lead to injury:

    1. Kinetic Energy (energy of motion)

    2. Electrical Energy

    3. Chemical Energy

    4. Thermal Energy

    5. Radiation Energy

  • Understanding Newton’s Laws:

    • 1st Law (Inertia): An object in motion remains in motion unless acted upon by an outside force.

    • 2nd Law: a=racFma = rac{F}{m} (Acceleration is proportional to force and inversely proportional to mass).

    • 3rd Law: For every action, there is an equal and opposite reaction; applies to forces during collisions.

G Forces in Collisions

  • G Forces Calculation: g=racv230dg = rac{v^2}{30d}

    • Where:

    • $v$ = velocity change (in mph)

    • $d$ = stopping distance (in feet)

  • Implications for safety engineering to minimize injuries.

Types of Collisions

Frontal Collisions:

  • Account for approximately 50% of motor vehicle deaths.

  • Involves three separate collisions:

    1. Vehicle impact (first collision)

    2. Occupant to interior impact (second collision)

    3. Organs within the body impacts during deceleration (third collision).

  • Typical Occupant Pathways:

    • Down and Under Sequence: Lower extremities impact the floor, followed by injury to the knees and upper torso hitting the steering wheel.

    • Up and Over Pathway: Upper body impacts the dashboard and steering wheel, then head impacts the windshield.

Rear Collisions:

  • Occur when a vehicle is struck from behind; less velocity change than frontal collisions.

  • Commonly results in whiplash injuries, particularly affected by the position of headrests.

Lateral Collisions (T-Bone):

  • Account for 25% of fatal collisions; high risk for passengers on the struck side.

  • Injuries typically sustained include rib fractures and abdominal organ injuries.

Angular and Rollover Collisions:

  • Angular collisions begin to resemble both frontal and lateral impacts in injury patterns.

  • Rollover collisions: Less severe than frontal collisions; often produce multiple small g forces rather than one large force.

Mechanisms of Injury

Blunt Trauma:

  • Common causes: motor vehicle collisions, falls, assaults.

  • Mechanisms leading to injury include:

    1. Tensile Strain: Extension beyond tissue limits.

    2. Shear Strain: Tissues subjected to opposing forces.

    3. Torsion: Twisting of tissues.

    4. Compression: Forces compressing tissues beyond limits.

Penetrating Trauma:

  • Gunshot wounds and knife wounds categorized as low vs. high velocity injuries.

  • Factors dictating severity:

    • Bullet velocity and path.

    • Surface area and density of the bullet.

Blast Injuries:

  • Comprise primary (shock waves), secondary (projectiles), tertiary (being hurled into objects), and associated (following environmental changes) injuries.

Clinical Applications and Implications

  • Understanding of kinetic energy is fundamental to predict injuries during trauma.

  • Importance of thorough scene assessment and history-taking is crucial in trauma care.

  • Recognition of injury patterns based on collision type leads to appropriate triage and intervention plans.

Conclusion

  • The integration of biomechanics principles is essential for treating trauma patients effectively and predicting potential injuries based on collision types and energy transfers. Understanding the dynamics involved in injuries will serve clinicians as they assess and manage trauma cases.