Cortical Bone Growth in Response to Local Strain Environment

Osteoporosis is a disease characterized by skeletal fragility resulting in increased risk of fracture. Millions of people are affected by osteoporotic fractures every year. Pharmaceutical drugs available in the current market have side-effects coming from long-term administration and adherence. While mechanical loading is known to be a critical factor during cortical bone growth, the type of mechanical loading a bone is subjected to during normal physiological condition can also affect bone development process.

It still is unclear whether tensile or compressive strains have better outcome in young cortical bone growth. In this study, juvenile sheep femur were scanned using micro-Computed Tomography (CT). Thickness and density were computed via image processing in MATLAB. Bone volume fraction (BV/TV) was determined through image processing in Amira. Samples along the longitudinal axis of diaphysis were machined and mechanically tested in three-point bending. Mechanical testing was done in two configurations: stain mode specific (SMS) (testing samples in habitual loading) and non-strain mode specific (testing samples in loading they are normally subjected to). Structure, composition, and material properties were investigated in two specific quadrants of femur diaphysis: anterior side subjected to tensile loading, and posterior side subjected to compressive loading during physiological activities.

There was no significant difference between cortical thickness and density of anterior and posterior quadrants. BV/TV was significantly higher in anterior quadrant compared to posterior quadrant in proximal diaphysis (p=0.016). Flexural modulus of anterior quadrant was higher than posterior only in distal diaphysis when tested in non-SMS condition (p=8E3). Anterior quadrant was always stronger than posterior quadrant regardless of testing mode (SMS: p=8E-3 proximal and middle diaphysis, non-SMS: p=8E-3 middle and distal diaphysis). Poor correlation was detected between density-modulus and density-strength (R² = 7.6% and R² = 11.3% respectively). BV/TV was more important in explaining the material properties than density: BV/TV-modulus R² = 10.7% and BV/TV-strength R² = 30.7%.

Year	Entry
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Year

Entry

2013

Weatherholt AM, Fuchs RK, Warden SJ. Cortical and trabecular bone adaptation to incremental load magnitudes using the mouse tibial axial compression loading model. Bone. January 2013;52(1):372-379.

1993

Riggs CM, Lanyon LE, Boyde A. Functional associations between collagen fibre orientation and locomotor strain direction in cortical bone of the equine radius. Anat Embryol. March 1993;187(3):231-238.

1979

Lanyon LE, Magee PT, Baggott DG. The relationship of functional stress and strain to the processes of bone remodelling: an experimental study on the sheep radius. J Biomech. 1979;12(8):593-600.

1976

Lanyon LE, Baggott DG. Mechanical function as an influence on the structure and form of bone. J Bone Joint Surg. November 1976;58B(4):436-443.

2015

Zimmermann EA, Busse B, Ritchie RO. The fracture mechanics of human bone: influence of disease and treatment. BoneKEy Rep. September 2015;4:743.