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Research Papers

Biomechanical Measurements of Stiffness and Strength for Five Types of Whole Human and Artificial Humeri

[+] Author and Article Information
Mina S. R. Aziz

Institute of Medical Science,
University of Toronto,
Toronto, ON M5S-1A8, Canada;
Martin Orthopaedic Biomechanics Lab,
St. Michael's Hospital,
Toronto, ON M5B-1W8, Canada

Bruce Nicayenzi, Meghan C. Crookshank

Martin Orthopaedic Biomechanics Lab,
St. Michael's Hospital,
Toronto, ON M5B-1W8, Canada

Habiba Bougherara

Department of Mechanical
and Industrial Engineering,
Ryerson University,
Toronto, ON M5B-2K3, Canada

Emil H. Schemitsch

Martin Orthopaedic Biomechanics Lab,
St. Michael's Hospital,
Toronto, ON M5B-1W8, Canada;
Faculty of Medicine,
University of Toronto,
Toronto, ON M5S-1A8, Canada

Radovan Zdero

Martin Orthopaedic Biomechanics Lab,
St. Michael's Hospital,
Li Ka Shing Building
(West Basement, Room B116),
209 Victoria Street,
Toronto, ON M5B-1W8, Canada;
Department of Mechanical
and Industrial Engineering,
Ryerson University,
Toronto, ON M5B-2K3, Canada
e-mail: zderor@smh.ca

1Corresponding author.

Manuscript received September 15, 2013; final manuscript received February 25, 2014; accepted manuscript posted April 10, 2014; published online April 10, 2014. Assoc. Editor: Tammy L. Haut Donahue.

J Biomech Eng 136(5), 051006 (Apr 10, 2014) (10 pages) Paper No: BIO-13-1429; doi: 10.1115/1.4027057 History: Received September 15, 2013; Revised February 25, 2014; Accepted April 10, 2014

The human humerus is the third largest longbone and experiences 2–3% of all fractures. Yet, almost no data exist on its intact biomechanical properties, thus preventing researchers from obtaining a full understanding of humerus behavior during injury and after being repaired with fracture plates and nails. The aim of this experimental study was to compare the biomechanical stiffness and strength of “gold standard” fresh-frozen humeri to a variety of humerus models. A series of five types of intact whole humeri were obtained: human fresh-frozen (n = 19); human embalmed (n = 18); human dried (n = 15); artificial “normal” (n = 12); and artificial “osteoporotic” (n = 12). Humeri were tested under “real world” clinical loading modes for shear stiffness, torsional stiffness, cantilever bending stiffness, and cantilever bending strength. After removing geometric effects, fresh-frozen results were 585.8 ± 181.5 N/mm2 (normalized shear stiffness); 3.1 ± 1.1 N/(mm2 deg) (normalized torsional stiffness); 850.8 ± 347.9 N/mm2 (normalized cantilever stiffness); and 8.3 ± 2.7 N/mm2 (normalized cantilever strength). Compared to fresh-frozen values, statistical equivalence (p ≥ 0.05) was obtained for all four test modes (embalmed humeri), 1 of 4 test modes (dried humeri), 1 of 4 test modes (artificial “normal” humeri), and 1 of 4 test modes (artificial “osteoporotic” humeri). Age and bone mineral density versus experimental results had Pearson linear correlations ranging from R = −0.57 to 0.80. About 77% of human humeri failed via a transverse or oblique distal shaft fracture, whilst 88% of artificial humeri failed with a mixed transverse + oblique fracture. To date, this is the most comprehensive study on the biomechanics of intact human and artificial humeri and can assist researchers to choose an alternate humerus model that can substitute for fresh-frozen humeri.

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Figures

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Fig. 1

Mechanical test setup for (a) shear stiffness, (b) torsional stiffness, and (c) cantilever bending stiffness and strength. Embalmed humeri are depicted, although the same setup was used for all groups. Arrows show load direction.

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Fig. 2

Absolute results. (a) shear stiffness, (b) torsional stiffness, (c) cantilever stiffness, and (d) cantilever strength. Symbols (*, #) indicate all statistical differences for pairwise comparisons (p < 0.05). Error bars are 1 standard deviation. FF = fresh-frozen humeri, EM = embalmed humeri, DR = dried humeri, AN = artificial “normal” humeri, AO = artificial “osteoporotic” humeri, and n = number of humeri used for analysis.

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Fig. 3

Normalized results. (a) shear stiffness, (b) torsional stiffness, (c) cantilever stiffness, and (d) cantilever strength. Symbols (*, #, §) indicate all statistical nondifferences for pairwise comparisons (p ≥ 0.05). Error bars are 1 standard deviation. FF = fresh-frozen humeri, EM = embalmed humeri, DR = dried humeri, AN = artificial “normal” humeri, AO = artificial “osteoporotic” humeri, and n = number of humeri used for analysis.

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Fig. 4

Failures of the humeral shaft: (a) embalmed humerus shaft with a typical oblique fracture starting on the tensile stress side and (b) artificial humerus shaft with a typical mixed transverse + oblique fracture.

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