title: The effect of in situ augmentation on implant anchorage in proximal humeral head fractures.
abstract: BACKGROUND
  Fracture fixation in patients suffering from osteoporosis is difficult as sufficient implant anchorage is not always possible. One method to enhance implant anchorage is implant/screw augmentation with PMMA-cement. The present study investigated the feasibility of implant augmentation with PMMA-cement to enhance implant anchorage in the proximal humerus.
  
  
  METHODS
  A simulated three part humeral head fracture was stabilised with an angular stable plating system in 12 pairs of humeri using six head screws. In the augmentation group the proximal four screws were treated with four cannulated screws, each augmented with 0.5ml of PMMA-cement, whereas the contra lateral side served as a non-augmented control. Specimens were loaded in varus-bending or axial-rotation using a cyclic loading protocol with increasing load magnitude until failure of the osteosynthesis occurred.
  
  
  RESULTS
  Augmented specimens showed a significant higher number of load cycles until failure than non-augment specimens (varus-bending: 8516 (SD 951.6) vs. 5583 (SD 2273.6), P=0.014; axial-rotation: 3316 (SD 348.8) vs. 2050 (SD 656.5), P=0.003). Non-augmented specimens showed a positive correlation of load cycles until failure and measured bone mineral density (varus-bending: r=0.893, P=0.016; axial-rotation: r=0.753, P=0.084), whereas no correlation was present in augmented specimens (varus-bending: r=0,258, P=0.621; axial-rotation r=0.127, P=0.810).
  
  
  CONCLUSIONS
  These findings suggest that augmentation of cannulated screws is a feasible method to enhance implant/screw anchorage in the humeral head. The improvement of screw purchase is increasing with decreasing bone mineral density.
authors: Department for Trauma Surgery, Medical University Innsbruck, Anichstrasse 35, A-6020 Innsbruck, Austria.
authors: Stefan
authors: S
authors: Unger
authors: Stefanie
authors: S
authors: Erhart
authors: Franz
authors: F
authors: Kralinger
authors: Michael
authors: M
authors: Blauth
authors: Werner
authors: W
authors: Schmoelz
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001843:Bone Cements; D015519:Bone Density; D001863:Bone Screws; D002102:Cadaver; D005240:Feasibility Studies; D005260:Female; D005592:Fracture Fixation / Q000379:methods; D006801:Humans; D058430:Humeral Head / Q000473:pathology / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D010024:Osteoporosis / Q000601:surgery*; D019904:Polymethyl Methacrylate; D012784:Shoulder Fractures / Q000601:surgery*
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate