title: Locking plate fixation of proximal humeral fractures with impaction of the fracture site to restore medial column support: a biomechanical study.
abstract: BACKGROUND
  Despite the advent of locking plate techniques, proximal humeral fracture fixation can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. This study investigated the effect of restoring the integrity of the medial column by fracture impaction and shaft medialization with locking plate fixation. This construct was compared with a traditional locking plate construct under conditions of varus cyclical loading.
  
  
  METHODS
  Proximal humeral fractures with medial comminution were simulated by performing wedge-shaped osteotomies at the surgical neck in cadaveric specimens and removing 1 cm of medial cortex. For each cadaver (n = 6), 1 humeral fracture was fixed with a traditional locking plate construct. The other was fixed with the locking plate construct plus fracture impaction and shaft medialization, resulting in medial column restoration. The humeral head was immobilized, and a repetitive, varus force was applied to the humeral shaft until construct collapse or until 25,000 cycles were completed.
  
  
  RESULTS
  None of the constructs with fracture impaction collapsed, whereas 5 of 6 of the nonaugmented constructs collapsed before reaching 25,000 cycles (P = .008). Collapse of the 5 nonimpacted constructs that failed occurred after an average of 11,470 ± 3589 cycles.
  
  
  CONCLUSIONS
  Fracture impaction increased the ability of the locking plate to withstand repetitive varus loading. This technique provides a construct biomechanically superior to locking plate fixation alone.
authors: Department of Orthopedic Surgery, University of Alberta, Edmonton, AB, Canada. Electronic address: cweeks1@ualberta.ca.
authors: Colleen A
authors: CA
authors: Weeks
authors: Farhana
authors: F
authors: Begum
authors: Lauren A
authors: LA
authors: Beaupre
authors: Jason P
authors: JP
authors: Carey
authors: Samer
authors: S
authors: Adeeb
authors: Martin J
authors: MJ
authors: Bouliane
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods*; D018460:Fractures, Comminuted / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012784:Shoulder Fractures / Q000601:surgery*
keywords: Basic science study; Biomechanics; Proximal humerus; biomechanical; complications; fracture; fracture impaction; locking plate; medial support