E3 Structure Bones

Topic

In general, this bone constitutes the rigid structural framework of the musculoskeletal system; consequently, within the context of sports biomechanics, it is modeled as a beam subjected to compression, tension, bending, torsion, or any combination thereof.

Cortical bone, by contrast, exhibits a considerably high modulus of elasticity and compressive strength—specifically, the ultimate compressive strength that defines the model for acute fractures—whereas trabecular bone is far more porous and softer than cortical bone, possessing a significantly lower modulus of elasticity.

Under the repetitive cyclic loading characteristic of the sport, the bone adapts through remodeling—in accordance with Wolff's Law—by aligning its internal structure with the principal stress lines traversing it. A stress fracture occurs precisely when this repetitive cyclic load exceeds the bone's capacity for microscopic repair; this type of fracture represents a scenario where the bone's remodeling capacity has been overwhelmed.

The cross-sectional second moment of area determines the bone's ultimate resistance to bending and its torsional rigidity, while the bone's length defines the lever arm for each acting muscle force—forces that constitute another key element of this biomechanical model. Consequently, in this model—where the bone is represented as a beam—the Euler-Bernoulli beam theory describes both the bone's final deflection and the final stress distribution within it under transverse loading, whereas Saint-Venant's theory describes the torsion to which the bone is subjected. If the bone instead sustains a sudden sports-related impact, a stress wave propagates at an extraordinarily high speed along the cortical bone, transmitting the instantaneous impact load well before the bone undergoes visible deformation.

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