title: Compressive Force With 2-Screw and 3-Screw Subtalar Joint Arthrodesis With Headless Compression Screws.
abstract: BACKGROUND
  Joint compression is an essential element of successful arthrodesis. Although subtalar joint compression generated by conventional screws has been quantified in the laboratory, compression obtainable with headless screws that rely on variable thread pitch to achieve bony contact has not been assessed. This study measured subtalar joint compression achieved by 2 posteriorly placed contemporary headless, variable-pitch screws, and quantified additional compression gained by placing a third screw anteriorly.
  
  
  METHODS
  Ten, unpaired fresh-frozen cadaveric subtalar joints were fixed sequentially using 2 diverging posterior screws (one directed into the talar dome, the other into the talar neck), 2 parallel posterior screws (both ending in the talar dome), and 2 parallel screws with an additional anterior screw inserted from the plantar calcaneus into the talar neck. Joint compression was quantified directly during screw insertion using a novel custom-built measuring device.
  
  
  RESULTS
  The mean compression generated by 2 diverging posterior screws was 246 N. Two parallel posterior screws produced 294 N of compression, and augmentation of that construct with a third, anterior screw increased compression to 345 N (P < .05). Compression subsequent to 2-screw fixation was slightly less than that reported previously for subtalar joint fixation with 2 conventional lag screws, but was comparable when a third screw was added.
  
  
  CONCLUSIONS
  Under controlled testing conditions, 2 tapered, variable-pitch screws generated somewhat less compression than previously reported for 2-screw fixation with conventional headed screws. A third screw placed anteriorly increased compression significantly.
  
  
  CONCLUSIONS
  Because headless screws are advantageous where prominent screw heads are problematic, such as the load-bearing surface of the foot, their effectiveness compared to other screws should be established to provide an objective basis for screw selection. Augmenting fixation with an anterior screw may be desirable when conditions for fusion are suboptimal.
authors: Department of Orthopaedic Surgery, The University of Tokyo, Tokyo, Japan.
authors: Takumi
authors: T
authors: Matsumoto
authors: Department of Orthopaedic Surgery, Duke University Medical Center, Durham, NC, USA.
authors: Richard R
authors: RR
authors: Glisson
authors: Department of Trauma Surgery, Hospital Wiener Neustadt, Wiener Neustadt, Austria.
authors: Markus
authors: M
authors: Reidl
authors: Department of Orthopaedic Surgery, Duke University Medical Center, Durham, NC, USA mark.e.easley@dm.duke.edu.
authors: Mark E
authors: ME
authors: Easley
mesh_terms: D001174:Arthrodesis / Q000295:instrumentation*; D001863:Bone Screws; D004867:Equipment Design; D006801:Humans; D055595:Mechanical Phenomena; D013380:Subtalar Joint / Q000601:surgery*
keywords: arthrodesis; compression; fusion; screw; subtalar