Blunt force

• Blunt Force Trauma

  Blunt force trauma (BFT) injuries are those typically sustained from  low-energy impacts resulting from a broad instrument delivered  over a relatively large surface area (Kimmerle and Baraybar, 2008)

  –This type of trauma can result from a variety of objects including  hammers, clubs, rocks and fists
• Blunt Force Trauma

  –Most blunt force injuries result from vehicular accidents or falls (Komar and Buikstra 2008, Reber and Simmons 2015)

  SWGANTH, 2011 Description:

  –‘blunt force trauma is produced by low velocity impact from a blunt object  or the low velocity impact of a body with a blunt surface’
• Factors

  • Skeletal manifestations of BFT encompass a wide variety of fracture  patterns which are determined by both intrinsic and extrinsic factors

  –Intrinsic factors

  •biomechanical properties of the bone, including morphology, density, buttressing,  microstructure, age etc.

  •Viscoelastic properties of fresh (wet) bone

  –Extrinsic factors

  •nature of the applied force and weapon characteristics including velocity, weight, distance,  object shape and loading duration also influence the resulting pattern of fracture
• Factors

  • The severity, extent, and appearance of blunt trauma injuries will  depend on:

  –The amount of force delivered to the body

  –The time over which the force is delivered

  –The region struck

  –The extent of body surface over which the force is delivered

  –The nature of the weapon

  –May include a combination of weapon and trauma types

  • Force dependant on kinetic energy (KE = ½ MV2)  smaller focus = less force needed to fracture
• Factors

  • Four categories of blunt force trauma defined in medicine:

  1.Abrasions

  2.Contusions

  3.Lacerations

  4.Fractures of the skeletal system
• Force: Elastic vs Plastic deformation

  • Biomechanically speaking, when a  force acts on a bone the bone will  react in predictable and  consecutive stages:

  –Stress, the force applied to the bone

  –Strain (elastic deformation), the  forces passing through the bone

  –Strain (plastic deformation), the  forces bending the bone with  permanent deformation

  –Failure, the fracture of the bone

  • These stages occur at both the  micro and macroscopic level

  
• Mechanical failure of bone

  •When bone encounters an object or surface, the  applied forces generally do not align with the  normal adaptive pattern – anisotropy

  •Consequently osseous deformations may result due to the tissue’s inability to dissipate the energy

  •The skeletal response to a loading force is  determined by the ability of bone to absorb the  applied energy and is described by Young’s modulus  of elasticity

  •During the initial phase of loading, elastic  deformation, the bone is subject to a degree of  force with which the bone is able to cope  competently
• Mechanical failure of bone

  •Once the force is released, the bone returns to its  original shape

  •If the applied force is increased and the yield point is  reached, plastic deformation occurs, resulting in a  permanent change to the bone structure and shape

  •Finally, once the applied force exceeds the point of  structural competency, the bone will fail, resulting in  fracture
• Mechanical failure of bone

  •In instances where the application of force occurs at  an increased velocity, the bone does not progress  through these stages, and instead immediately fails

  •This is commonly observed in cases of ballistic or  explosive trauma
• Slow vs Rapid Load Application

  • Slow vs rapid load application can be understood as how much time the bone has to bend and react (deform) before it fails

  • In slow loading trauma, there is more time for the bone to bend

  –Therefore, significant deformation is typical of BFT

  • In rapid loading trauma, there is minimal deformation of skeletal tissue

  –Fragments fit together more easily.
• Slow vs Rapid Load Application

  •Tested equine bone at quasistatic and dynamic  strain rates

  –Quasistatic (slower) rates produced much more tortuous fracturing and rough fracture surface.

  –Dynamic (faster) loading conditions produced much straighter fractures with less peripheral  damage and a smoother fracture surface.

  •Results suggest a rate dependent change in  the properties of collagen from brittle to  ductile as strain rate increases