title: Mechanical stability of a locked step-plate versus single compression screw fixation for medial displacement calcaneal osteotomy.
abstract: BACKGROUND
  Reconstruction of a flatfoot commonly involves a calcaneal Medial Displacement Osteotomy (MDO) to correct hindfoot valgus in combination with soft tissue procedures. We compared fixation of an MDO using either a single, large cannulated screw versus a locking step-plate in load to failure in a cadaveric model.
  
  
  METHODS
  Eight matched pairs of cadaveric limbs were loaded using a mechanical testing rig. Two pairs served as non-operated controls. The remaining paired limbs underwent a 10-mm MDO stabilized either with a single 7-mm screw or a step-plate with four locking screws. One pair was used as a pilot study and the remaining five pairs were loaded up to 4500 N to failure.
  
  
  RESULTS
  In the five pairs loaded to failure, the median (with 95% CI) maximum force were 1779 N (1099-2312) and 826 N (288-1607) for the plate and screw, respectively (p = 0.043). With single screw fixation, the tuberosity fragment consistently failed by rotation and angulation into varus. With plate fixation, failure occurred as the screws cut through the internal surfaces of the tuberosity and body with no failure at the screw-plate interface.
  
  
  CONCLUSIONS
  In this cadaveric model, a locked step-plate supported a significantly higher maximum force than a single large cannulated screw.
  
  
  CONCLUSIONS
  The magnitude of the load supported by the locking step-plate suggests that allowing early weightbearing post-operation may be safe in clinical practice before union of the osteotomy.
authors.affiliation: University College London Hospital NHS Foundation Trust, UK.
authors.forename: Sujith
authors.initials: S
authors.lastname: Konan
authors.forename: Jay
authors.initials: J
authors.lastname: Meswania
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Blunn
authors.forename: Rohit T
authors.initials: RT
authors.lastname: Madhav
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Oddy
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D002111:Calcaneus / Q000601:surgery*; D005260:Female; D005413:Flatfoot / Q000601:surgery; D006801:Humans; D008297:Male; D008422:Materials Testing; D010027:Osteotomy / Q000379:methods*; D011474:Prosthesis Design; D013314:Stress, Mechanical; D016474:Weight-Bearing