Torsion - an underestimated form shaping entity in bone adaptation?

OBJECTIVES: There is ample agreement that the specific shape of a bone is related to the loads it has to carry. It is also believed that bones mechano-adapt in order to ‘find’ this shape. The open question is which signals constitute the determinants of this adapation. Recent in vivo experiments show that torsion is a significant load component in human tibia, and a computational study of the mechanostat has indicated that torsion could play a role in the shaping of tubular long bones. METHODS: An earlier computational approach is further progressed to systematically study the relative importance of axial compression, lateral bending and axial torsion. RESULTS: Results demonstrate that shape-driving potential towards tubular shapes is greatest for torsion, followed by bending and least for axial compression. Multiple linear regression analysis confirmed the dominant role of torsion, in particular for the 2(nd) moment of intertia. The obtained results were largely unaffected by starting conditions, e.g. either from a grid or through reshaping under disuse. CONCLUSIONS: Strong support has been found for the hypothesis torsion could be more important than suggested in previous studies as a component of the mechanical environment of bones. This will apply to the shafts of long bones, and also to the femoral neck.