Effects of loading rate on strength of the proximal femur

Abstract

Results from previous quasi-static mechanical tests indicate that femurs from elderly subjects fail in vitro at forces 50% below those available in a fall from standing height. However, bone is a rate-dependent material, and it is not known whether this imbalance is present at rates of loading which occur in a fall. Based on recent data on time to peak force and body positions at impact during simulated falls, we designed a high rate test of the femur in a loading configuration meant to represent a fall on the hip. We used elderly (mean age 73.5 +/- 7.4 (SD) years) and younger adult (32.7 +/- 12.8 years) cadaveric femurs to investigate whether (1) the strength, stiffness, and energy absorption capacity of the femur increases under high rate loading conditions; (2) elderly femurs have reduced strength, stiffness, and energy absorption capacity compared with younger adult femurs at this loading rate; and (3) densitometric and geometric measures taken at the hip correlate with the measured fracture loads. Femurs were scanned using dual-energy X-ray absorptiometry (DXA) and then tested to failure in a fall loading configuration at a displacement rate of 100 mm/second. The fracture load in elderly and younger adult femurs increased by about 20% with a 50-fold increase in displacement rate. However, energy absorption did not increase with displacement rate because of a twofold increase in stiffness at the higher loading rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonlinear quasi-static finite element simulations predict in vitro strength of human proximal femora assessed in a dynamic sideways fall setup

“…In particular, the mean stiffness and maximal load was 46% and 75% higher, respectively, in the dynamic experiments compared to the quasi-static simulations, with the outlier excluded. An experimental study using proximal femora of elderly donors reported that a 50-fold increase in the displacement rate resulted in an approximately 20% larger fracture load and 100% higher stiffness, but no differences in energy absorption capacity (Courtney et al, 1994). These results only partially explain the dynamic experimental vs. quasi-static numerical discrepancies observed in the present study.…”

“…stiffer and stronger, but more brittle) under impact-compared to quasi-static loading conditions (Carter and Hayes, 1977). Accordingly, the stiffness and fracture force of whole bones are strain rate dependent (Courtney et al, 1994). Additionally, in drop-tower test configurations that aim to better mimic sideways falling accidents, the rate of loading is a function of the sample's stiffness .…”

Contemporary management of femoral neck fractures: the young and the old

“…An estimated 1.66 million hip fractures occurred in 1990, and of these, 0.28 million occurred in the United States. According to epidemiologic projections, this worldwide annual number will rise to 6.26 million by 2050 [53,54]. Many of these patients present with multiple medical comorbidities, which has continued to spark debate regarding the optimal treatment algorithm for this population.…”

Exercise loading history and femoral neck strength in a sideways fall: A three-dimensional finite element modeling study

“…To simulate sideways falling, the most commonly used force direction from previous experimental studies [10,32,33] was chosen. The femoral shaft was tilted at 10° with respect to the ground and the femoral neck was internally rotated by 15° (Fig.…”

“…The femoral shaft was tilted at 10° with respect to the ground and the femoral neck was internally rotated by 15° (Fig. 2) [10,32,33]. The individual impact force was estimated using the equation proposed by Bouxsein et al [34]:…”