title: Straight proximal humeral nails are surrounded by more bone stock in comparison to bent nails in an experimental cadaveric study.
abstract: BACKGROUND
  In the management of proximal humeral fractures intramedullary implants with bent and straight shape of the proximal part of nail are available. Based on data from previous studies on bone distribution in the humeral head, we hypothesized, that higher densities might exist in the bone stock surrounding straight nails in comparison to their angulated counterparts. With a known positive correlation between bone density and mechanical stability, this could indicate potentially higher rigidity of osteosyntheses done with straight implants.
  
  
  METHODS
  We performed high resolution peripheral quantitative computed tomographies of the potential straight and bent implant bearing regions of 27 cadaveric proximal humeri. The acquired data were analyzed for differences between straight and bent Volumes of Interest as well as intra- and interindividual bone stock distribution.
  
  
  RESULTS
  For both straight and bent volumes of interest a considerably declining bone mineral density was found in craniocaudal direction. Mean densities of bent volumes were significantly lower in comparison to their corresponding straight counterparts (p < 0.01) Intra-individual comparison yielded high bivariate correlations of the corresponding Volumes of Interest of the right and the left side (p < 0.01).
  
  
  CONCLUSIONS
  Based on the volumetric data a statistically relevant biomechanical superiority of straight shaped implants can be assumed. Since we found a rapid decrease of bone density in cranio-caudal direction, intramedullary implants should be anchored as proximally in the subcortical area as possible to minimize the risk of displacement or cutout. The high correlation between the Volumes of Interest of the corresponding right and left sides could aid in preoperative planning when considering an intra- or extramedullary approach.
authors.affiliation: University Hospital of Munich, Department of Orthopaedic Surgery, Physical Medicine and Rehabilitation - Campus Großhadern, Ludwig-Maximilians-University, Marchioninistr. 15, 81377 Munich, Germany.
authors.forename: Christian Max
authors.initials: CM
authors.lastname: Günther
authors.affiliation: University Hospital of Munich, Department of Orthopaedic Surgery, Physical Medicine and Rehabilitation - Campus Großhadern, Ludwig-Maximilians-University, Marchioninistr. 15, 81377 Munich, Germany.
authors.forename: Peter Ernst
authors.initials: PE
authors.lastname: Müller
authors.affiliation: University Hospital of Munich, Department of Trauma Surgery - Campus Innenstadt, Ludwig-Maximilians-University, Nußbaumstr. 20, 80336 Munich, Germany.
authors.forename: Wolf
authors.initials: W
authors.lastname: Mutschler
authors.affiliation: AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland.
authors.forename: Christoph Martin
authors.initials: CM
authors.lastname: Sprecher
authors.affiliation: Anatomische Anstalt, Ludwig-Maximilians-University, Pettenkoferstraße 11, 80336 Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Milz
authors.affiliation: University Hospital of Munich, Department of Trauma Surgery - Campus Innenstadt, Ludwig-Maximilians-University, Nußbaumstr. 20, 80336 Munich, Germany ; Sportsclinic Germany, Ottobrunnerstrasse 55, 81737 Munich, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Braunstein
keywords: Bent vs. straight proximal humeral nails; Bone stock; Reduce risk of implant failure