title: The effect of bone quality on the stability of ankle arthrodesis. A finite element study.
abstract: BACKGROUND
  Despite uniform operating techniques, lack of fusion still occurs after ankle arthrodesis. Differences in the biological healing potential may be a factor but the mechanical performance of the arthrodesis construct because of varying bone quality also may be important. Internal compression techniques are preferred because of higher union rates, shorter fusion times, and fewer complications. A three-screw configuration has been shown to be more stable than a two-screw configuration, but it is not obvious when it should be used.
  
  
  METHODS
  Three-dimensional finite element models of intact and flat-cut ankle arthrodeses were built, using two and three screws in different configurations. Poor bone quality was simulated by decreasing Young's modulus of the bone. The constructs were loaded in torsion and dorsiflexion, and micromotions at the fusion site were measured.
  
  
  RESULTS
  Bone quality had a marked effect on the stability at the arthrodesis site. Inserting two screws at 30 degrees relative to the longitudinal axis of the tibia in an intact arthrodesis seemed the best option, especially as bone quality worsened. The addition of a third screw increased the stability at the arthrodesis site.
  
  
  CONCLUSIONS
  Overall, intact joint surfaces and three-screw fixation, with the lateral and medial screws inserted produced the most stable arthrodesis constructs when bone quality was poor. CLINICAL RELEVANCE. Ankle arthrodeses are technically demanding because of the shape and small size of the talus. Preoperative planning is an absolute necessity to determine placement and number of screws. This study shows that poor bone quality decreases the stability of the arthrodesis constructs, suggesting that an attempt should be made to create the most stable three-screw configuration. Finite element models can be used as an effective preoperative tool for planning screw number and placement.
authors.affiliation: Bioengineering Sciences Research Group, School of Engineering Sciences, University of Southhampton, Southampton SO17 1BJ, UK.
authors.forename: Ana
authors.initials: A
authors.lastname: Alonso-Vázquez
authors.forename: Henrik
authors.initials: H
authors.lastname: Lauge-Pedersen
authors.forename: Lars
authors.initials: L
authors.lastname: Lidgren
authors.forename: Mark
authors.initials: M
authors.lastname: Taylor
mesh_terms: D000843:Ankle Joint / Q000601:surgery*; D001174:Arthrodesis / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena; D001863:Bone Screws; D020342:Finite Element Analysis; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D008954:Models, Biological