Similarity in the fatigue behavior of trabecular bone across site and species

Short-term femoral neck fracture is a primary complication associated with contemporary hip resurfacing. Some fractures are associated with neck notching, while others occur in the absence of notching. These unexplained fractures may be due to large magnitude strains near the implant rim, which could cause bone damage accumulation and eventual neck fracture. We used statistically augmented finite element analysis to identify design and environmental variables that increase bone strains near the implant rim after resurfacing, and lead to strain magnitudes sufficient for rapid damage accumulation. After resurfacing, the compressive strains in the inferior, peripheral neck increased by approximately 25%, particularly when the implant shell was bonded. While the tensile strains in the peripheral neck were low in magnitude in the immediate postoperative models, they increased substantially following compressive damage accumulation. Low bone modulus, within the range of normal bone, and high head load contributed the most to large magnitude strains. Therefore, in some cases, hip resurfacing may cause a region of compressive bone damage to develop rapidly, which in turn leads to large tensile strains and potential neck fracture. Our study suggests that indications for surgery should account for bone material quality, and that rehabilitation protocols should avoid high-load activities. ß

Section: Discussionmentioning

confidence: 65%

Hip resurfacing increases bone strains associated with short‐term femoral neck fracture

Long

Santner

Bartel

2009

“…By design, the mean age of our donors was higher than other studies, and the age range was smaller than previous studies. 33,[39][40][41][42][43][44]46 Because we limited our sample to elderly donors, our results are not likely to be representative of the general population, but rather of an elderly population. This is important to consider when interpreting our results, as a study with a larger age range (i.e., young to old) may have different findings.…”

Section: Discussionmentioning

confidence: 98%

“…[39][40][41][42][43] Additionally, our low measurements could be due to differences in testing methodologies, anatomic site and/or donor age. 33,34,[39][40][41][42][43][44][45] We note that our relationship between BV/TV and elastic modulus appears weaker than that in several other studies, where 60-80% of the variability in elastic modulus is explained by volume fraction. This FACTORS INFLUENCING HUMAN VERTEBRAL TRABECULAR BONE MECHANICS may be due to the limited age range (and therefore bone density) of our donors compared to previously published studies, as a broader age (and density) range would likely lead to a higher correlation coefficient.…”

Section: Discussionmentioning

confidence: 99%

Effects of preexisting microdamage, collagen cross‐links, degree of mineralization, age, and architecture on compressive mechanical properties of elderly human vertebral trabecular bone

Follet

Viguet-Carrin

Burt‐Pichat

et al. 2010

Previous studies have shown that the mechanical properties of trabecular bone are determined by bone volume fraction (BV/ TV) and microarchitecture. The purpose of this study was to explore other possible determinants of the mechanical properties of vertebral trabecular bone, namely collagen cross-link content, microdamage, and mineralization. Trabecular bone cores were collected from human L2 vertebrae (n ¼ 49) from recently deceased donors 54-95 years of age (21 men and 27 women). Two trabecular cores were obtained from each vertebra, one for preexisting microdamage and mineralization measurements, and one for BV/TV and quasi-static compression tests. Collagen cross-link content (PYD, DPD, and PEN) was measured on surrounding trabecular bone. Advancing age was associated with impaired mechanical properties, and with increased microdamage, even after adjustment by BV/TV. BV/TV was the strongest determinant of elastic modulus and ultimate strength (r 2 ¼ 0.44 and 0.55, respectively). Microdamage, mineralization parameters, and collagen cross-link content were not associated with mechanical properties. These data indicate that the compressive strength of human vertebral trabecular bone is primarily determined by the amount of trabecular bone, and notably unaffected by normal variation in other factors, such as crosslink profile, microdamage and mineralization. Keywords: bone strength; microdamage; microarchitecture; mineralization; collagen cross-links; vertebral trabecular bone Several studies have shown that the mechanical properties of trabecular bone are influenced by bone volume fraction (BV/TV) and microarchitecture. 1,2 However, additional factors, such as degree of mineralization, preexisting microdamage, and collagen cross-link profile may also play a role, yet the contribution of these factors to human trabecular bone mechanical properties remains incompletely understood.Increased mineralization of cortical bone is exponentially related to increased stiffness, but decreased energy absorption. 3 A similar trend was seen in human trabecular bone from the calcaneus, with a positive relationship between mineralization and elastic modulus, after adjusting for BV/TV. 4 It has also been suggested that a reduction in the heterogeneity of mineralization density distribution leads to increased bone fragility, 5 but there are few data to support this assertion.Microdamage has been largely studied in animal models and in human cortical bone, with only a few studies reporting microdamage in human trabecular bone either naturally occurring 6-11 or due to loading ex-vivo. 12 In cortical bone, microdamage accumulation leads to decreased mechanical properties, 13,14 and therefore has been implicated in skeletal fragility and stress fractures. 15 However, the association between microdamage and cortical bone fracture toughness was weak, 16 raising questions as to the role of microdamage in cortical bone. Increased microdamage has also been associated with decreased strength in human vertebral cancellous bone; 1...

“…Some investigators 28,34,35 choose a percentage of stiffness loss as the criterion for failure. We initially selected 15% loss of stiffness as the failure criterion, a likely range for significant microcrack accumulation.…”

Section: Discussionmentioning

confidence: 99%

Sex differences in long bone fatigue using a rat model

Moreno

Waldman

Grynpas

2006

Stress fractures can occur because of prolonged exercise and are associated with cyclic loading. Fatigue is the accumulated damage that results from cyclic loading and bone fatigue damage is of special concern for athletes and army recruits. Existing literature shows that the rates of stress fracture for female athletes and female army recruits are higher than their male counterparts. In this study, we used an ex vivo rat model to investigate the fatigue response of female and male bones. We determined the strain versus number of cycles to failure (S/N) for each sex and found that for a certain initial strain (5,000-7,000 me) female bones have shorter fatigue life. To further characterize the bone response to fatigue, we also determined the creep that occurred during the fatigue test. From the creep data, for a certain strain range, female bones accumulated greater residual strains and reached the critical strain at a faster rate. In summary, this study demonstrates that female rat bones have a lower resistance to fatigue in the absence of a physiological response such as muscle fatigue or osteogenic adaptation. From these results, we hypothesized that creep was the underlying mechanism that accounted for the fast deterioration of female bones during fatigue.