title: Retrograde nailing versus locking plate osteosynthesis of proximal humeral fractures: a biomechanical study.
abstract: BACKGROUND
  In locking plate osteosynthesis of proximal humeral fractures, secondary varus malalignment is a specific complication. Retron nails (Tantum AG, Neumunster, Germany), among others, have been designed to improve medial support of the calcar humeri. The aim of our biomechanical study was to examine whether Retron nails provide increased stiffness for axial loads and adequate stiffness for torsional loads when compared with Philos plates (Synthes AG, Umkirch, Germany).
  
  
  METHODS
  Twenty-two fresh-frozen paired humeri were collected. After potting the specimens, intact bones were exposed to sinusoidal axial (10-120 N) and torsional (±2.5 Nm) loading for 8 cycles to calculate the initial stiffness and exclude pairs with differences. Afterward, an unstable proximal humeral fracture (AO 11-A3) was created by means of an oscillating saw, and the respective osteosynthesis devices were implanted. After another 4 cycles, initial changes in stiffness were measured. Subsequently, all specimens were tested for 1,000 cycles of loading before final stiffness was assessed.
  
  
  RESULTS
  We found no statistically significant differences between Retron and Philos specimens after 4 or 1,000 cycles of loading.
  
  
  CONCLUSIONS
  Our study suggests that retrograde nailing provides sufficient stability for axial and torsional loading in 2-part fractures of proximal humeri.
authors.affiliation: Center for Musculoskeletal Surgery, Department of Trauma Surgery, University Medical Center, Johannes Gutenberg University, Mainz, Germany. sven-oliver.dietz@unimedizin-mainz.de
authors.forename: Sven-Oliver
authors.initials: SO
authors.lastname: Dietz
authors.forename: Frank
authors.initials: F
authors.lastname: Hartmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwarz
authors.forename: Tobias E
authors.initials: TE
authors.lastname: Nowak
authors.forename: Annalisa
authors.initials: A
authors.lastname: Enders
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kuhn
authors.forename: Alexander
authors.initials: A
authors.lastname: Hofmann
authors.forename: Pol Maria
authors.initials: PM
authors.lastname: Rommens
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D001860:Bone Plates; D001863:Bone Screws; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D011474:Prosthesis Design; D011859:Radiography; D012784:Shoulder Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*