title: Mechanical evaluation of a new minimally invasive device for stabilization of proximal humeral fractures in elderly patients: a cadaver study.
abstract: BACKGROUND
  Treatment of proximal humerus fractures in elderly patients is challenging because of reduced bone quality. We determined the in vitro characteristics of a new implant developed to target the remaining bone stock, and compared it with an implant in clinical use.
  
  
  METHODS
  Following osteotomy, left and right humeral pairs from cadavers were treated with either the Button-Fix or the Humerusblock fixation system. Implant stiffness was determined for three clinically relevant cases of load: axial compression, torsion, and varus bending. In addition, a cyclic varus-bending test was performed.
  
  
  RESULTS
  We found higher stiffness values for the humeri treated with the ButtonFix system--with almost a doubling of the compression, torsion, and bending stiffness values. Under dynamic loading, the ButtonFix system had superior stiffness and less K-wire migration compared to the Humerusblock system.
  
  
  CONCLUSIONS
  When compared to the Humerusblock design, the ButtonFix system showed superior biomechanical properties, both static and dynamic. It offers a minimally invasive alternative for the treatment of proximal humerus fractures.
authors.affiliation: Center for Musculoskeletal Surgery, Charité-Universitätsmedizin, Berlin, Germany. georg.duda@charite.de
authors.forename: Georg N
authors.initials: GN
authors.lastname: Duda
authors.forename: Devakara R
authors.initials: DR
authors.lastname: Epari
authors.forename: Reto
authors.initials: R
authors.lastname: Babst
authors.forename: Simon M
authors.initials: SM
authors.lastname: Lambert
authors.forename: Romano
authors.initials: R
authors.lastname: Matthys
authors.forename: Norbert P
authors.initials: NP
authors.lastname: Südkamp
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008297:Male; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation*; D012784:Shoulder Fractures / Q000601:surgery*; D016474:Weight-Bearing