title: Ultimate fracture load of cadaver proximal humeri correlates more strongly with mean combined cortical thickness than with areal cortical index, DEXA density, or canal-to-calcar ratio.
abstract: OBJECTIVE
  This investigation sought to advance the work published in our prior biomechanical study (Journal of Orthopaedic Research, 2016). We specifically sought to determine whether there are additional easy-to-measure parameters on plain radiographs of the proximal humerus that correlate more strongly with ultimate fracture load, and whether a parameter resembling the Dorr strength/quality characterisation of proximal femurs can be applied to humeri.
  
  
  METHODS
  A total of 33 adult humeri were used from a previous study where we quantified bone mineral density of the proximal humerus using radiographs and dual-energy x-ray absorptiometry (DEXA), and regional mean cortical thickness and cortical index using radiographs. The bones were fractured in a simulated backwards fall with the humeral head loaded at 2 mm/second via a frustum angled at 30° from the long axis of the bone. Correlations were assessed with ultimate fracture load and these new parameters: cortical index expressed in areas ("areal cortical index") of larger regions of the diaphysis; the canal-to-calcar ratio used analogous to its application in proximal femurs; and the recently described medial cortical ratio.
  
  
  RESULTS
  The three new parameters showed the following correlations with ultimate fracture load: areal cortical index (r = 0.56, p < 0.001); canal-to-calcar ratio (r = 0.38, p = 0.03); and medial cortical ratio (r = 0.49, p < 0.005). These correlations were weaker when compared with those that we previously reported: mean cortical thickness of the proximal diaphysis versus ultimate fracture load (r = 0.71; p < 0.001); and mean density in the central humeral head versus ultimate fracture load (r = 0.70; p < 0.001).
  
  
  CONCLUSIONS
  Simple-to-measure radiographic parameters of the proximal humerus reported previously are more useful in predicting ultimate fracture load than are areal cortical index, canal-to-calcar ratio, and medial cortical ratio.Cite this article: J. G. Skedros, C. S. Mears, W. Z. Burkhead. Ultimate fracture load of cadaver proximal humeri correlates more strongly with mean combined cortical thickness than with areal cortical index, DEXA density, or canal-to-calcar ratio. Bone Joint Res 2017;6:1-7. DOI: 10.1302/2046-3758.61.BJR-2016-0145.R1.
authors.affiliation: The W.B. Carrell Memorial Clinic, Dallas, Texas, USA jskedrosmd@uosmd.com.
authors.forename: J G
authors.initials: JG
authors.lastname: Skedros
authors.affiliation: Department of Orthopaedics and Utah Orthopaedic Specialists, University of Utah, Salt Lake City, Utah, USA.
authors.forename: C S
authors.initials: CS
authors.lastname: Mears
authors.affiliation: The W.B. Carrell Memorial Clinic, Dallas, Texas, USA.
authors.forename: W Z
authors.initials: WZ
authors.lastname: Burkhead
keywords: Canal-to-calcar ratio; Cortical index; Dual-energy x-ray absorptiometry; Fracture; Humerus; Osteoporosis