title: Biomechanical analysis of a novel locking plate with smooth pegs versus a conventional locking plate with threaded screws for proximal humerus fractures.
abstract: BACKGROUND
  Repair of proximal humeral fractures with locking plates has greatly improved outcomes. However, an alarming rate of complications including screw cutout and impingement under the acromion has recently been reported. A novel locking plate with smooth pegs was developed to reduce these risks. The purpose of this study was to compare these 2 fixation methods with a cadaveric biomechanical study.
  
  
  METHODS
  Fourteen pairs of cadaveric proximal humeri (mean age, 77 years) were harvested, and bone density was measured. Osteosynthesis was performed on each pair using either a locking plate with threaded screws (TS group) or smooth pegs (SP group) on the contralateral side. Seven pairs of humeri were tested for cyclic bending, and 7 pairs for cyclic torsional evaluation: TS bending, SP bending, TS torsion, and SP torsion. The bending protocol consisted of cyclically loading to a maximum of 7.5 Nm bending moment for 10,000 cycles. The torsion protocol consisted of ±2 Nm of axial torque for 10,000 cycles. Surgical neck fractures were simulated by excising a 10-mm wedge of bone.
  
  
  RESULTS
  No implant failure or screw cutout was observed in any of the groups tested. Under bending loads, mean displacement of the distal fragment was significantly less for the SP group than that for the TS group over 5,000 cycles. In torsion tests, no significant differences were observed between the 2 fixation methods.
  
  
  CONCLUSIONS
  The SP group demonstrated superior biomechanical characteristics to the TS group in regards to cyclic bending.
authors: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors: Nobuyuki
authors: N
authors: Yamamoto
authors: Michio
authors: M
authors: Hongo
authors: Lawrence J
authors: LJ
authors: Berglund
authors: John W
authors: JW
authors: Sperling
authors: Robert H
authors: RH
authors: Cofield
authors: Kai-Nan
authors: KN
authors: An
authors: Scott P
authors: SP
authors: Steinmann
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012784:Shoulder Fractures / Q000503:physiopathology* / Q000601:surgery*