title: Mechanical performance of a screw-type veterinary suture anchor subjected to single load to failure and cyclic loads.
abstract: OBJECTIVE
  To characterize the mechanical performance of a veterinary bone anchor under static and cyclic loads.
  
  
  METHODS
  Mechanical testing study.
  
  
  METHODS
  Cadaveric canine humeri.
  
  
  METHODS
  Humeri (6 pairs) were collected from skeletally mature dogs (mean [+/-SD] age, 17.2+/-2.1 months; weight, 20.8+/-1.5 kg). Bone anchors were inserted in the proximal metaphysis using nylon, and were longitudinally extracted. For the opposite humerus, anchors were subjected to longitudinal cyclic load (50% of the load at failure of their pair) for 1200 cycles then longitudinally loaded to failure. Anchors were then installed in a similar and adjacent area of these 2(nd) humeri with nylon and cyclically tested perpendicular to the axis of anchor insertion (100% of the longitudinal holding power of their pair) for 1200 cycles, then perpendicularly loaded to failure. Paired t-tests were used to compare holding power before and after longitudinal cyclic testing.
  
  
  RESULTS
  Longitudinal holding power of the screw-type anchor in the proximal humerus was 385+/-30 N. Anchor pullout was the only mode of failure. Anchors in the paired humeri did not fail after 1200 cycles of 50% longitudinal loading, and post-cycle holding strength was not different (335+/-87 N; P=.32). Perpendicularly loaded anchors did not fail after 1200 cycles of 100% of opposite longitudinal holding strength, and had post-cycle perpendicular holding strengths of 514+/-72 N. Suture breakage was the mode of failure.
  
  
  CONCLUSIONS
  Bone anchor holding strength is dependent on orientation of suture load. Screw-type bone anchor holding strength was not affected by longitudinal cyclic loading, and holding strengths of approximately 385 N can be expected in metaphyseal bone of large-breed mature dogs. Perpendicularly loaded anchors have higher failure loads, and holding strength of approximately 514 N can be expected in metaphyseal bone of the proximal humerus.
authors.affiliation: Department of Clinical Sciences, Tufts University School of Veterinary Medicine, 200 Westboro Road, N. Grafton, MA 01536, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Balara
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McCarthy
authors.forename: Randy J
authors.initials: RJ
authors.lastname: Boudrieau
authors.forename: Karl H
authors.initials: KH
authors.lastname: Kraus
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000662:veterinary*; D002102:Cadaver; D004285:Dogs / Q000293:injuries* / Q000601:surgery; D005260:Female; D005594:Fracture Fixation, Intramedullary / Q000379:methods / Q000662:veterinary*; D006810:Humeral Fractures / Q000601:surgery*; D013536:Suture Techniques / Q000662:veterinary