title: Injury tolerance of the wrist and distal forearm to impact loading onto outstretched hands.
abstract: BACKGROUND
  The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tolerance of the wrist is poorly understood. This study sought to quantify the injury tolerance of the adult male forearm-wrist complex under loading simulating axial impact to an outstretched hand.
  
  
  METHODS
  Fifteen isolated cadaveric forearm/wrist specimens were tested. Loading was applied via an instrumented drop tower device designed to impact the palmar surface of the hand with the wrist extended to approximately 90 degrees. Impact severity was modulated by adjusting the boundary condition of the elbow. Elbow reaction force and deformation of the specimen (deflection of the palmar surface of the hand toward the elbow) were measured. Bone-implanted strain gauges were used to detect the time of fracture. Injury risk functions were developed using parametric survival analysis with a cumulative Weibull distribution.
  
  
  RESULTS
  Of 14 specimens, 10 exhibited a fracture to the wrist or forearm after test (one specimen was excluded from the analysis). Injury severities varied from nondisplaced fractures of the radius to severely displaced fractures and/or fracture-dislocations of the carpal bones. Of the potential predictors studied, the specimen deflection expressed as a percentage of the initial specimen length produced the injury risk model of best fit (50% risk of fracture at 1.69% deflection; 95% confidence interval, 1.38-2.07% deflection). The value of the elbow reaction force corresponding to a 50% risk of injury was 4.34 kN (3.80-4.97 kN).
  
  
  CONCLUSIONS
  These results provide information for the prediction of wrist and forearm injury in biomechanical models simulating impacts in the field and provide tolerance information for the development of injury mitigation countermeasures.
authors.affiliation: From the University of Virginia Center for Applied Biomechanics (J.F.), Charlottesville, Virginia; University of Virginia Center for Applied Biomechanics (B.P.), Charlottesville, Virginia; University of Virginia Center for Applied Biomechanics (A.A.), Charlottesville, Virginia; University of Virginia Department of Orthopaedics (A.F.) and the University of Virginia Hand Center, Charlottesville, Virginia; University of Virginia Center for Applied Biomechanics (R.S.), Charlottesville, Virginia; and Applied Research Associates (T.W.), Littleton, Colorado.
authors.forename: Jason
authors.initials: J
authors.lastname: Forman
authors.forename: Brandon
authors.initials: B
authors.lastname: Perry
authors.forename: Aaron
authors.initials: A
authors.lastname: Alai
authors.forename: Aaron
authors.initials: A
authors.lastname: Freilich
authors.forename: Robert
authors.initials: R
authors.lastname: Salzar
authors.forename: Tim
authors.initials: T
authors.lastname: Walilko
mesh_terms: D000328:Adult; D002102:Cadaver; D004550:Elbow; D005543:Forearm Injuries / Q000209:etiology*; D006230:Hand Injuries / Q000209:etiology*; D006801:Humans; D015601:Injury Severity Score; D008297:Male; D008875:Middle Aged; D011187:Posture; D011885:Radius Fractures / Q000209:etiology; D012307:Risk Factors; D013314:Stress, Mechanical; D014458:Ulna Fractures / Q000209:etiology; D014954:Wrist Injuries / Q000209:etiology*