Residual strength of equine bone is not reduced by intense fatigue loading: implications for stress fracture.
Abstract: Fatigue or stress fractures are an important clinical problem in humans as well as racehorses. An important question in this context is, when a bone experiences fatigue damage during extreme use, how much is it weakened compared to its original state? Since there are very limited data on this question and stress fractures are common in racehorses, we sought to determine the effect of fatigue loading on the monotonic strength of equine cortical bone. Beams were machined from the dorsal, medial and lateral cortices of the third metacarpal bones of six thoroughbred racehorses. Beams from left and right bones were assigned to control and fatigue groups, respectively (N = 18 each). The fatigue group was cyclically loaded in three-point bending at 2 Hz for 100,000 cycles at 0-5000 microstrain while submerged in saline at 37 degrees C. These beams, as well as those in the control group, were then monotonically loaded to failure in three-point bending. The monotonic load-deflection curves were analyzed for differences using three-factor (fatigue loading, anatomic region, and horse) analysis of variance. The mean failure load was 3% less in the fatigue group, but this reduction was only marginally significant. Neither elastic modulus nor yield strength was significantly affected by the fatigue loading. The principal effects of fatigue loading were on post-yield behavior (yield being based on a 0.02% offset criterion). The work done and the load increase between yield and failure were both significantly reduced. All the variables except post-yield deflection were significantly affected by anatomic region. In summary, loading equivalent to a lifetime of racing does not significantly weaken equine cortical bone ex vivo. The clinical implication of this may be that the biological repair of fatigue damage can actually contribute to stress fracture if pressed too far.
Publication Date: 1997-02-01 PubMed ID: 9001930DOI: 10.1016/s0021-9290(96)00113-3Google Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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The research article explores the impact of intense fatigue loading on the residual strength of equine bone, and its relevance to stress fractures, primarily in racehorses. It concludes that a lifetime of racing doesn’t considerably weaken the equine bone’s strength.
Study Design and Methodology
- The study was conducted using beams of bone obtained from the dorsal, medial, and lateral cortices of the third metacarpal bones of six thoroughbred racehorses.
- The beams from the left and right bones were selected for the control and fatigue groups, with 18 samples assigned to each group.
- The fatigue group underwent cyclical loading in a three-point bending test at a frequency of 2 Hz for 100,000 cycles at a strain range of 0 to 5000 microstrains while submerged in saline at a temperature of 37 degrees Celsius. The aim was to replicate the extreme conditions that lead to fatigue damage in the bone.
- Beams from both the fatigue group and the control group were then subject to monotonic loading until failure, using a three-point bending test.
- The reactions of the two groups under the monotonic load were then compared and analysed to identify any differences.
Research Findings
- The results showed only a marginal reduction (3%) in the mean failure load in the fatigue group compared to the control group, indicating that intense fatigue loading does not significantly reduce the monotonic strength of equine bone.
- Neither the elastic modulus, which measures the stiffness of a material, nor the yield strength, which is the maximum stress that can be applied without causing permanent deformation, were significantly affected by the fatigue loading.
- The principal impact of fatigue loading was seen in post-yield behaviour. The work done and the increase in load between yield and failure were noticeably reduced.
- Additionally, apart from post-yield deflection, all other variables were significantly affected by the anatomical region of the bone.
Implications of the Research
- The study implies that racing does not significantly weaken equine bone, though it impacts post-yield behaviour.
- This suggests that the biological repair of fatigue damage, if pushed too far, could contribute to the occurrence of stress fractures.
Cite This Article
APA
Martin RB, Gibson VA, Stover SM, Gibeling JC, Griffin LV.
(1997).
Residual strength of equine bone is not reduced by intense fatigue loading: implications for stress fracture.
J Biomech, 30(2), 109-114.
https://doi.org/10.1016/s0021-9290(96)00113-3 Publication
Researcher Affiliations
- Orthopedic Research Laboratories, School of Medicine, University of California at Davis 95616, USA.
MeSH Terms
- Analysis of Variance
- Animals
- Bone Remodeling / physiology
- Bone and Bones / physiopathology
- Elasticity
- Female
- Fractures, Stress / physiopathology
- Horses / physiology
- Linear Models
- Male
- Metacarpus / physiopathology
- Stress, Mechanical
- Tensile Strength
- Wound Healing
Grant Funding
- AR41644 / NIAMS NIH HHS
Citations
This article has been cited 5 times.- Noble P, Singer ER, Jeffery NS. Does subchondral bone of the equine proximal phalanx adapt to race training?. J Anat 2016 Jul;229(1):104-13.
- Fletcher L, Codrington J, Parkinson I. Effects of fatigue induced damage on the longitudinal fracture resistance of cortical bone.. J Mater Sci Mater Med 2014 Jul;25(7):1661-70.
- Garrison JG, Gargac JA, Niebur GL. Shear strength and toughness of trabecular bone are more sensitive to density than damage.. J Biomech 2011 Nov 10;44(16):2747-54.
- Leng H, Dong XN, Wang X. Progressive post-yield behavior of human cortical bone in compression for middle-aged and elderly groups.. J Biomech 2009 Mar 11;42(4):491-7.
- Wang X, Nyman JS. A novel approach to assess post-yield energy dissipation of bone in tension.. J Biomech 2007;40(3):674-7.
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