title: Ballistic fractures: indirect fracture to bone.
abstract: BACKGROUND
  Two mechanisms of injury, the temporary cavity and the sonic wave, have been proposed to produce indirect fractures as a projectile passes nearby in tissue. The purpose of this study is to evaluate the temporal relationship of pressure waves using strain gauge technology and high-speed video to elucidate whether the sonic wave, the temporary cavity, or both are responsible for the formation of indirect fractures.
  
  
  METHODS
  Twenty-eight fresh frozen cadaveric diaphyseal tibia (2) and femurs (26) were implanted into ordnance gelatin blocks. Shots were fired using 9- and 5.56-mm bullets traversing through the gelatin only, passing close to the edge of the bone, but not touching, to produce an indirect fracture. High-speed video of the impact event was collected at 20,000 frames/s. Acquisition of the strain data were synchronized with the video at 20,000 Hz. The exact time of fracture was determined by analyzing and comparing the strain gauge output and video.
  
  
  RESULTS
  Twenty-eight shots were fired, 2 with 9-mm bullets and 26 with 5.56-mm bullets. Eight indirect fractures that occurred were of a simple (oblique or wedge) pattern. Comparison of the average distance of the projectile from the bone was 9.68 mm (range, 3-20 mm) for fractured specimens and 15.15 mm (range, 7-28 mm) for nonfractured specimens (Student's t test, p = 0.036).
  
  
  CONCLUSIONS
  In this study, indirect fractures were produced after passage of the projectile. Thus, the temporary cavity, not the sonic wave, was responsible for the indirect fractures.
authors.affiliation: Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan 48109, USA. pauldough@med.umich.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Dougherty
authors.forename: Don
authors.initials: D
authors.lastname: Sherman
authors.forename: Nathan
authors.initials: N
authors.lastname: Dau
authors.forename: Cynthia
authors.initials: C
authors.lastname: Bir
mesh_terms: D000368:Aged; D002102:Cadaver; D016009:Chi-Square Distribution; D005264:Femoral Fractures / Q000503:physiopathology*; D005269:Femur / Q000293:injuries*; D005780:Gelatin; D006801:Humans; D011312:Pressure; D013977:Tibia / Q000293:injuries*; D013978:Tibial Fractures / Q000503:physiopathology*; D014741:Video Recording; D014948:Wounds, Gunshot / Q000503:physiopathology*
chemical_list: D005780:Gelatin