title: Biomechanical study: determining the optimum insertion angle for screw-in suture anchors-is deadman's angle correct?
abstract: OBJECTIVE
  To assess the effect of the insertion angle and the angle of applied load on the pullout strength of screw-in suture anchors.
  
  
  METHODS
  Screw-in metallic suture anchors were inserted into a 10-lb/cu ft synthetic cancellous bone block at 30°, 45°, 60°, and 90° to the surface. The suture pull angle was then varied in 30° increments between 0° and 180°. Five constructs were tested to failure (anchor pullout) for each combination of angles using a Zwick tensile testing machine (Zwick Roell, Ulm, Germany).
  
  
  RESULTS
  There were a total of 25 combinations. The greatest pullout strength was seen with a suture anchor inserted at 90° to the bone block with a pull angle of 90° to the bone (mean, 306 N; standard deviation [SD], 9 N). The weakest pullout strength was seen with a suture anchor inserted at 30° with the angle of pull at 120° (i.e., opposite to the direction of insertion of the anchor) (mean, 97 N; SD, 11 N). A simulated deadman's angle of 45° with an angle of pull of 150° produced a pullout strength of 127 N (SD, 4 N). The pullout strengths for each insertion angle were greatest when the angle of pull was similar to the angle of insertion (P < .0001, repeated-measures analysis of variance).
  
  
  CONCLUSIONS
  The angle of applied load to a suture anchor and the insertion angle significantly influence the biomechanical pullout strength of screw-in suture anchors. The insertion angle of the suture anchor should replicate the angle of applied load to ensure the optimum pullout strength.
  
  
  CONCLUSIONS
  The screw-in anchor insertion angle and angle of applied load may have an influence on pullout strength.
authors.affiliation: Department of Orthopaedics, Northern Deanery, Newcastle-upon-Tyne, England. Electronic address: nicholasgreen@doctors.org.uk.
authors.forename: Robert N
authors.initials: RN
authors.lastname: Green
authors.affiliation: Yeovil District Hospital, Yeovil, England.
authors.forename: Oliver W
authors.initials: OW
authors.lastname: Donaldson
authors.affiliation: Department of Radiology, Welsh Deanery, Cardiff, Wales.
authors.forename: Meilyr
authors.initials: M
authors.lastname: Dafydd
authors.affiliation: School of Engineering, Cardiff University, Cardiff, Wales.
authors.forename: Sam L
authors.initials: SL
authors.lastname: Evans
authors.affiliation: Royal Gwent Hospital, Newport, Wales.
authors.forename: Rohit
authors.initials: R
authors.lastname: Kulkarni
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001863:Bone Screws; D006801:Humans; D008422:Materials Testing; D055585:Physical Phenomena; D013314:Stress, Mechanical; D053441:Suture Anchors; D013536:Suture Techniques; D013537:Sutures