A study into alternative bone remodelling under tension and compression in the proximal femur after one year of hopping exercises using quantitative computerised tomography and finite element simulation
Creators: name: TAYLOR, MATTHEW ROBERT
Publisher: name: University of Surrey
Year: 2021

description: Bone remodelling is an important process with numerous clinical implications. It is generally
description: assumed that the bone will experience the same bone remodelling response to the stimulus under
description: tension and compression. However, laboratory studies suggest that the bone could exhibit
description: alternative bone remodelling under tension and compression as the result of different bone
description: remodelling mechanisms; where alternative bone remodelling is defined as two or more
description: different/alternative bone remodelling responses in relation to the same stimulus. Here, tension
description: and compression are assumed to be the same stimulus, where the absolute value of the strain
description: stimulus is used. Very little research has been conducted into this phenomenon and if it occurs
description: under physiologically applied loading conditions. Therefore, it is unclear how prevalent alternative
description: bone remodelling is under physiological loading conditions.
description: To investigate if the bone does exhibit alternative bone remodelling under tension and compression
description: under physiological loading conditions, this study examined the bone remodelling behaviour of
description: the proximal femur of 11 male subjects (mean age ± SD: 70.91 ± 2.78) taking part in a one-year
description: hopping clinical exercise trial. This was achieved by comparing the change in density of each
description: subject, measured by quantitative computerised tomography, against the mechanical stimulus,
description: determined by subject specific finite element simulations. Here the stimulus was determined to be
description: the principal strain experienced in hopping minus the principal strain experienced during everyday
description: activities which were either walking or stair climbing. The stimulus-remodelling relationships
description: were determined by comparing the change in density and stimulus using a previously published
description: bone remodelling algorithm.
description: This study managed to demonstrate consistent differences in the bone remodelling observed under
description: tension and compression. Where it was observed that at lower stimuli the compressive regions
description: experience a higher change in density in relation to the stimulus in comparison to the tensile
description: regions, until a cross-over point where tension experiences a higher change in density in
description: comparison to compression (p &lt; 0.01). This cross over point occurs at a stimulus of approximately
description: 670 µε which corresponds to a change in density of approximately 3.5%, which is higher than the
description: typical change in density experienced in the cortical bone during exercise. This cross over between
description: the two stimulus-remodelling relationships is thought to be the result of the Hueter-Volkmann law.
description: It was also observed that the bone remodelling under compression has a higher variance in the
description: change in density in relation to the stimulus, in comparison to tension (p &lt; 0.01), which is thought
description: to the be result of linear microdamage formation and subsequent remodelling initiation under
description: compression. This high variance in the change in density under compression causes for the
description: stimulus-remodelling relationships under tension and compression to merge somewhat at lower
description: stimuli, which can give the impression of a single stimulus-remodelling relationship. Furthermore,
description: differences in the residual regression biases under tension and compression was observed, where
description: the bone remodelling under tension demonstrated significantly lower regression biases in
description: comparison to the bone remodelling under compression (p = 0.141).
description: Evidence from this study also suggests that the tensile and compressive stimulus-remodelling
description: relationships are independent of each other, but correlations of varying strength were made
description: between the observed characteristics and the subjects’ age and BMI, with the correlations being
description: typically stronger under tension. However further research is warranted into these correlations due
description: to the small sample size and population demographic used in this study.