Mechanics and Classification of Athletic Injuries

• acute injury is caused by mechanical failure of soft tissue due to excessive force occurring in a single bout
• acute injury occurs with sudden onset of short duration
• chronic injury occurs with mechanical failure of soft tissue due to repeated micro-trauma occurring over an extended period of time
• chronic injury has a gradual onset and are of prolonged duration
• an open wound is exposed and breaks the surface of the skin
• a closed wound is unexposed and is any injury that does not involve disruption of the skin surface
• load/stress is external/internal force acting on the tissue
• degree of deformation depends on:

  • tissue composition
  • speed of applied load
  • frequency of loading
  • direction of loading
• yield point is when load is greater than mechanical capabilities of the tissue
• yield point is where mechanical failure begins to occur
• six primary mechanical forces that cause injury: tension, compression, shear, bending, torsion, combined
• tension creates a pulling action trying to elongate the structure
• examples of tension injuries include: sprained ankle and biceps tendinitis
• compression creates a pushing action tending to shorten the structure
• examples of compression injuries: spinal compression fracture, carpal tunnel, shoulder impingement
• shear force: forces that acts parallel to the cross section or surface of a body (two forces are in opposite directions)
• examples of shear injuries: olecranon bone spurs, fossa shearing, radio-capitellar compression
• combined loading includes bending and torsion
• bending: loading about an axis - combination of tension and compression
• torsion: load applied causing structure to twist about an axis
• examples of torsion injuries: ACL, femur shaft fracture, fibula fracture
• more bone mass = more bone strength
• Wolff's Law: bones will adapt to the degree of mechanical loading
• sudden bone shape changes are areas where mechanical stresses are most concentrated
• bone strength direction of loading goes from compression > tension > shear
• bones are suited for tensile force at the ends and compressive force in the middle
• description of fracture:

  • site: bone name, diaphysis/epiphysis
  • extent: partial, complete
  • configuration: transverse, oblique, spiral, etc
  • relationship of fragments: displaced or nondisplaced
  • relationship to environment: open, closed
• fracture caused by a direct blow?

  transverse
• fracture caused by rotation on planted foot?

  spiral
• fracture caused by one end fixed, other sudden torsion?

  oblique
• fracture caused by blow or fall in awkward position?

  comminuted
• fracture caused with flat bones, direct blow?

  depressed
• incomplete fracture, skeletally immature (convex)?

  greenstick
• fracture that splits along length, caused by jumping from height?

  longitudinal
• fracture caused by direct blow, has jagged edges?

  serrated
• fracture on side opposite to point of impact?

  contrecoup
• fracture caused by compressive force on long axis of bone?

  impacted
• rib contusion/fracture are both caused by a blow to the rib cage, but more severe if a fracture
• rib fracture can also occur with compression of the rib cage (football and wrestling)
• ribs 5-9 are most commonly fractured