title: Biomechanical comparison of the trocar tip point and the hollow ground tip point for smooth external skeletal fixation pins.
abstract: OBJECTIVE
  To compare the insertional characteristics of external fixator pins with hollow ground (HG), modified HG, and trocar (T) points.
  
  
  METHODS
  An acute, in vitro biomechanical evaluation.
  
  
  METHODS
  Thirteen radii from canine cadavers.
  
  
  METHODS
  A total of 16 T-tipped and 16 HG-tipped pins were inserted into 8 canine radii. Ten pins of each modification of the HG tip (length of the cutting edge reduced by 0.127 mm and 0.254 mm, respectively) were inserted into another five radii. All pins were inserted with low-speed power drilling and 80 N drilling load. Differences between peak tip temperature, drilling energy, and pullout force were determined for each pin type at both diaphyseal and metaphyseal locations.
  
  
  RESULTS
  HG-tipped pins showed a 40% lower tip temperature in diaphyseal bone, a 25% reduction in drilling energy in diaphyseal bone, and a reduction of pullout force in both diaphyseal (65%) and metaphyseal (50%) bone compared with T-tipped pins. HG 0.254-mm pins generated higher tip temperatures and had greater pullout than HG pins in diaphyseal bone.
  
  
  CONCLUSIONS
  The HG tip was a more efficient design; however, the reduction in pullout force suggests that, because a better hole was drilled, radial preload is reduced. Reduction of the cutting edge by 0.254 mm increased the pullout force but also increased the temperatures.
  
  
  CONCLUSIONS
  Thermal and microstructural damage are reduced by the HG tip, but pin-bone interface stability is also compromised. The use of a tip with 0.254 mm reduction in the cutting edge may optimize the biological and mechanical factors at the pin-bone interface.
authors.affiliation: Department of Companion Animal and Special Species Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh 27606, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Marti
authors.forename: S C
authors.initials: SC
authors.lastname: Roe
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000592:standards*; D002102:Cadaver; D004285:Dogs / Q000601:surgery*; D005592:Fracture Fixation / Q000295:instrumentation / Q000662:veterinary*; D011884:Radius / Q000601:surgery*