title: Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation.
abstract: OBJECTIVE
  Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws.
  
  
  METHODS
  Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder.
  
  
  RESULTS
  There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant.
  
  
  CONCLUSIONS
  There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model.
  
  
  CONCLUSIONS
  Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.
authors.affiliation: Department of Orthopaedic Surgery, Sports Medicine and Rehabilitation, Wright State University, Boonshoft School of Medicine, Dayton, OH, USA. rossaf44@yahoo.com
authors.forename: Ross A
authors.initials: RA
authors.lastname: Schumer
authors.forename: Kara L
authors.initials: KL
authors.lastname: Muckley
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Markert
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Prayson
authors.forename: Jonathan
authors.initials: J
authors.lastname: Heflin
authors.forename: Emmanuel K
authors.initials: EK
authors.lastname: Konstantakos
authors.forename: Tarun
authors.initials: T
authors.lastname: Goswami
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001860:Bone Plates / Q000592:standards*; D001863:Bone Screws / Q000592:standards; D002102:Cadaver; D019245:Compressive Strength; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D006811:Humerus / Q000503:physiopathology* / Q000601:surgery; D008422:Materials Testing; D010027:Osteotomy; D011474:Prosthesis Design; D015203:Reproducibility of Results; D012784:Shoulder Fractures / Q000503:physiopathology / Q000601:surgery*; D054159:Torsion, Mechanical