title: Screw augmentation reduces motion at the bone-implant interface: a biomechanical study of locking plate fixation of proximal humeral fractures.
abstract: BACKGROUND
  Shear forces at the bone-implant interface lead to a loss of reduction after locking plate fixation of proximal humeral fractures. The aim of the study was to analyze the roles of medial support screws and screw augmentation in failure loads and motion at the bone-implant interface after locking plate fixation of proximal humeral fractures.
  
  
  METHODS
  Unstable 3-part fractures were simulated in 6 pairs of cadaveric humeri and were fixed with a DiPhos-H locking plate (Lima Corporate, Udine, Italy). An additional medial support screw was implanted in 1 humerus of every donor. The opposite humerus was stabilized with a medial support screw and additional bone cement augmentation of the 2 anteriorly directed head screws. Specimens were loaded in the varus bending position. Stiffness, failure loads, plate bending, and the motion at the bone-implant interface were evaluated using an optical motion capture system.
  
  
  RESULTS
  The mean load to failure was 669 N (standard deviation [SD], 117 N) after fixation with medial support screws alone and 706 N (SD, 153 N) after additional head screw augmentation (P = .646). The initial stiffness was 453 N/mm (SD, 4.16 N/mm) and 461 N/mm (SD, 64.3 N/mm), respectively (P = .594). Plate bending did not differ between the 2 groups. However, motion at the bone-implant interface was significantly reduced after head screw augmentation (P < .05).
  
  
  CONCLUSIONS
  The addition of bone cement to augment anteriorly directed head screws does not increase stiffness and failure loads but reduces motion at the bone-implant interface. Thus, the risk of secondary dislocation of the head fragment may be reduced.
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany. Electronic address: benedikt.schliemann@gmail.com.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Schliemann
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Seifert
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Steffen B
authors.initials: SB
authors.lastname: Rosslenbroich
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Theisen
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Wähnert
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Raschke
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Münster, Münster, Germany.
authors.forename: Andre
authors.initials: A
authors.lastname: Weimann
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001860:Bone Plates; D001863:Bone Screws; D000069343:Bone-Implant Interface / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012784:Shoulder Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D014057:Tomography, X-Ray Computed
chemical_list: D001843:Bone Cements
keywords: PEEK plate; Proximal humerus fracture; augmentation; bone cement; humeral head fracture; locking plate fixation