title: A comparison of parallel and diverging screw angles in the stability of locked plate constructs.
abstract: We investigated the static and cyclical strength of parallel and angulated locking plate screws using rigid polyurethane foam (0.32 g/cm(3)) and bovine cancellous bone blocks. Custom-made stainless steel plates with two conically threaded screw holes with different angulations (parallel, 10° and 20° divergent) and 5 mm self-tapping locking screws underwent pull-out and cyclical pull and bending tests. The bovine cancellous blocks were only subjected to static pull-out testing. We also performed finite element analysis for the static pull-out test of the parallel and 20° configurations. In both the foam model and the bovine cancellous bone we found the significantly highest pull-out force for the parallel constructs. In the finite element analysis there was a 47% more damage in the 20° divergent constructs than in the parallel configuration. Under cyclical loading, the mean number of cycles to failure was significantly higher for the parallel group, followed by the 10° and 20° divergent configurations. In our laboratory setting we clearly showed the biomechanical disadvantage of a diverging locking screw angle under static and cyclical loading.
authors.affiliation: University Hospital Münster, Department of Trauma Surgery, Waldeyerstrasse 1, Münster 48149, Germany. dirk.waehnert@aofoundation.org
authors.forename: D
authors.initials: D
authors.lastname: Wähnert
authors.forename: M
authors.initials: M
authors.lastname: Windolf
authors.forename: S
authors.initials: S
authors.lastname: Brianza
authors.forename: S
authors.initials: S
authors.lastname: Rothstock
authors.forename: R
authors.initials: R
authors.lastname: Radtke
authors.forename: V
authors.initials: V
authors.lastname: Brighenti
authors.forename: K
authors.initials: K
authors.lastname: Schwieger
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology; D001860:Bone Plates; D001863:Bone Screws; D002417:Cattle; D019544:Equipment Failure Analysis; D005269:Femur / Q000601:surgery; D020342:Finite Element Analysis; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006614:Hindlimb / Q000601:surgery; D016268:Internal Fixators; D008954:Models, Biological; D011183:Postoperative Complications / Q000517:prevention & control; D013314:Stress, Mechanical