title: Interfragmentary compression profile of 4 headless bone screws: an analysis of the compression lost on reinsertion.
abstract: OBJECTIVE
  To evaluate the interfragmentary compression force generated by 4 different types of headless compression screws and to examine the effects of removal and reinsertion of the screw.
  
  
  METHODS
  We chose foot bones rather than scaphoids for the model because they were larger and would enable comparison of 2 screw designs in the same bone, thereby controlling for the effect of interspecimen variability. A transverse osteotomy was made in 10 fresh-frozen cadaveric navicular bones and 10 medial cuneiforms. A load cell was used to measure compression between the 2 fragments as a screw was inserted across the fracture. Each bone was tested twice, with an Acutrak Mini (Acumed, Hillsboro, OR; n = 10) and an SBi AutoFIX screw (SBi, Morrisville, PA; n = 10) or an Extremifix (Osteomed, Addison, TX; n = 10) and a Barouk screw (Depuy, Warsaw, IN; n = 10). Compression was recorded at initial insertion and on removal and reinsertion of the screw twice to the same position. Compression was also measured after one additional full turn further than the initial position.
  
  
  RESULTS
  The mean interfragmentary compression generated by the Acutrak Mini screw was greater than that of the SBi AutoFIX screw (96 N vs 22 N). There was a trend toward a greater mean compression generated by the Extremifix screw compared to the Barouk screw (85 N vs 22 N). There was a significant loss of compression upon removal and reinsertion of the screws. An additional full turn of the screw was able to re-establish a large proportion of the original compression.
  
  
  CONCLUSIONS
  The compression forces achieved by headless screw systems appeared to vary according to the screw design, depth of insertion, and the quality of the bone. Substantial compression was lost if the screw was removed and replaced. Some screw designs appeared to require a greater depth of insertion to achieve effective compression, and the number of additional turns required to re-establish compression might vary according to the thread design.
  
  
  CONCLUSIONS
  Surgeons should be aware of the compression profile of each screw design and the effect of screw removal and reinsertion in the clinical setting of small bone fixation.
authors.affiliation: Department of Hand Surgery, Singapore General Hospital, Singapore.
authors.forename: A W
authors.initials: AW
authors.lastname: Gardner
authors.forename: Y T
authors.initials: YT
authors.lastname: Yew
authors.forename: P Y
authors.initials: PY
authors.lastname: Neo
authors.forename: C C
authors.initials: CC
authors.lastname: Lau
authors.forename: S C
authors.initials: SC
authors.lastname: Tay
mesh_terms: D001863:Bone Screws / Q000592:standards*; D019245:Compressive Strength; D020878:Device Removal; D004867:Equipment Design; D004868:Equipment Failure; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D010027:Osteotomy; D013639:Tarsal Bones / Q000601:surgery