title: Biomechanical effects of calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures.
abstract: BACKGROUND
  The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest.
  
  
  METHODS
  Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples.
  
  
  RESULTS
  The mechanical effect of additional calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws.
  
  
  CONCLUSIONS
  Additional calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
authors.affiliation: Department of Trauma and Reconstructive Surgery, Diakoniekrankenhaus Friederikenstift gGmbH, Humboldtstr. 5, 30169 Hannover, Germany. Electronic address: christoph.katthagen@ddh-gruppe.de.
authors.forename: Jan Christoph
authors.initials: JC
authors.lastname: Katthagen
authors.affiliation: Laboratory of Biomechanics and Biomaterials, Medizinische Hochschule Hannover (MHH), Anna-von-Borries-Str. 1-7, 30625 Hannover, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schwarze
authors.affiliation: Department of Trauma and Reconstructive Surgery, Diakoniekrankenhaus Friederikenstift gGmbH, Humboldtstr. 5, 30169 Hannover, Germany.
authors.forename: Josefin
authors.initials: J
authors.lastname: Meyer-Kobbe
authors.affiliation: Department of Trauma and Reconstructive Surgery, Diakoniekrankenhaus Friederikenstift gGmbH, Humboldtstr. 5, 30169 Hannover, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Voigt
authors.affiliation: Laboratory of Biomechanics and Biomaterials, Medizinische Hochschule Hannover (MHH), Anna-von-Borries-Str. 1-7, 30625 Hannover, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Hurschler
authors.affiliation: Department of Trauma and Reconstructive Surgery, Diakoniekrankenhaus Friederikenstift gGmbH, Humboldtstr. 5, 30169 Hannover, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Lill
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001703:Biophysics; D015519:Bone Density; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005270:Femur Head / Q000601:surgery; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D050723:Fractures, Bone / Q000601:surgery; D006801:Humans; D058430:Humeral Head / Q000601:surgery*; D006811:Humerus / Q000601:surgery*; D008875:Middle Aged; D009989:Orthotic Devices; D012784:Shoulder Fractures / Q000601:surgery*; D013314:Stress, Mechanical
keywords: Bone augmentation; Calcar screw; Dynamic locking screw; Fracture; Medial support; Proximal humerus