Abstract
The reported work is a part of an ongoing research program concerned with structural analysis of fractured long bone and methods of internal fixation. The stress-concentration factors for equine metacarpus bones containing greenstick fractures and “through” fractures (surgically repaired) were determined for the compression, flexural and torsional modes of loading based on whole bone (unfractured) strengths. The greenstick type of fracture was simulated with saw cuts at the mid-span of the bone, and the parameters varied were depth of fracture and orientation of fracture. All specimens consisted of fresh dead bone which had been placed in a freezer within 4 hr after expiration. The maximum stress-concentration factors for the simulated greenstick fractures studied were about 3.4 for compression, 4.3 for torsion and 16 for flexure. The stressconcentration factors for fractured bones surgically repaired with commercial plates were about 3.0 for compression, 2.7 for torsion and 6.1 for flexure.
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Abbreviations
- A :
-
cross-sectional area of bone at midlength, in
- a 1,a 2 :
-
major radius of outer and inner ellipse, respectively, in
- b 1,b 2 :
-
minor radius of outer and inner ellipse, respectively, in
- c :
-
distance from neutral axis to outer fiber, flexure, in
- d 1,d 2 :
-
eccentricity of minor ellipse fromx andy axis, respectively, in
- k 1,k 2 :
-
aspect ratios for outer and inner ellipse, respectively, numeric
- \(\bar k\) :
-
average aspect ratio of outer and inner ellipses, numeric
- e :
-
distance from support to fracture tip, in
- F u ,F g ,F p :
-
ultimate force in flexure for unfractured bone, greenstick fracture and plated bone, respectively, kip
- GL :
-
gage length, in
- I xn8 ,I yn8 :
-
area moment of inertia aboutx neutral axis andy neutral axis, respectively, in
- L :
-
total length of bone, in
- LF :
-
load factor, percent
- MR u ,MR g ,MR p :
-
modulus of rupture for unfractured bone, greenstick fracture and plated bone, respectively, ksi
- P u ,P g ,P p :
-
ultimate force in compression for unfractured bone, greenstick fracture and plated bone, respectively, kip
- R :
-
fracture ratio,s/2b 1, percent
- SCF :
-
stress-concentration factor, numeric
- s :
-
crack depth, in
- T u ,T g ,T p :
-
ultimate torque for unfractured bone, greenstick fracture and plated bone, respectively, kip
- TR u ,TR g ,TR p `:
-
torsional modulus for unfractured, greenstick fracture and plated bone, respectively, ksi
- \(\bar x, \bar y\) :
-
distance fromy andx axis, respectively, of major ellipse to neutral surface, in
- ϕ:
-
angle of fracture, deg
- σ u , σ o , σ p :
-
ultimate strength in compression for unfractured bone and plated bone, respectively, ksi
References
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Bynum, D., Ledbetter, W.B., Boyd, C.L. et al. Parametric stress-concentration factors in greenstick bone fracture. Experimental Mechanics 10, 474–480 (1970). https://doi.org/10.1007/BF02327675
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DOI: https://doi.org/10.1007/BF02327675