title: The role of medial comminution and calcar restoration in varus collapse of proximal humeral fractures treated with locking plates.
abstract: BACKGROUND
  Proximal humeral fractures that are treated with locked plate constructs remain susceptible to collapse into a varus position. The objectives of the present study were to examine how medial comminution affects fracture stability and to determine the effect of calcar fixation on osteosynthesis stability.
  
  
  METHODS
  Eleven matched pairs of cadaveric humeri were osteotomized to create standard three-part fractures involving the surgical neck and the greater tuberosity. Five matched pairs were randomly assigned to have the medial calcar region remain intact. Six matched pairs had removal of a 10-mm medially based wedge of bone to simulate medial comminution. All fractures were stabilized in a uniform fashion with a proximal humeral locking plate. The constructs were secured, and the superior portion of the humeral head was subjected to compressive loading to induce varus collapse. Load-to-failure and energy-to-failure values along with stiffness and displacement at the time of failure were determined.
  
  
  RESULTS
  Medial comminution decreased the mean load to failure by 48% (523 N) (p = 0.015) and the mean energy to failure by 44% (2009 Nmm) (p = 0.013). The use of calcar screw fixation increased the mean load to failure by 31% (219 N) (p = 0.002) and the mean energy to failure by 44% (1279 Nmm) (p = 0.006).
  
  
  CONCLUSIONS
  Medial comminution significantly decreased the stability of proximal humeral fracture fixation constructs. Calcar restoration with screw fixation significantly improved the stability of repaired fractures in cadaveric specimens.
  
  
  CONCLUSIONS
  The data suggest that medial comminution is a predictor of poor stability of proximal humeral fractures and that stability may be improved through calcar restoration.
authors: Division of Orthopaedic Surgery, University of Alabama at Birmingham, Birmingham, AL 35205, USA. bponce@aumbc.edu
authors: Brent A
authors: BA
authors: Ponce
authors: Kevin J
authors: KJ
authors: Thompson
authors: Parthasarathy
authors: P
authors: Raghava
authors: Alan W
authors: AW
authors: Eberhardt
authors: Janet P
authors: JP
authors: Tate
authors: David A
authors: DA
authors: Volgas
authors: James P
authors: JP
authors: Stannard
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D005593:Fracture Fixation, Internal; D006801:Humans; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012784:Shoulder Fractures / Q000601:surgery*; D016474:Weight-Bearing