DIFFERENCES IN CORTICAL FIBULA AND TIBIA STRUCTURE BETWEEN LONG-DISTANCE RUNNERS AND UNTRAINED CONTROLS. TOWARD A WIDER INSIGHT OF MECHANOSTAT FUNCTION.

LAURA NOCCIOLINO; SERGIO LUSCHER; ALEX IRELAND; JOERN RITTWEGER; NICOLÁS PILOT; LEANDRO PISANI; LEANDRO MACKLER; JOSÉ LUIS FERRETTI; GUSTAVO ROBERTO COINTRY; RICARDO FRANCISCO CAPOZZA

Orlando

Congreso; ASBMR 2019 Annual Meeting; 2019

American Society for Bone & Mineral Research

The cortical structure of the human fibula varies widely throughout the bone, showing no less than five different arrangements concerning the relationships between bone mass, geometry and strength indicators. This is highly suggestive of a greater adaptative capacity of the fibula to different mechanical environments with respect to the adjacent tibia, and that fibula adaptations may show some regional specificity.To test this hypothesis, serial-pQCT scans (taken at every 5% of the tibia length) of the dominant fibulae and tibiae of 15/15 men/women chronically trained in long-distance running were compared with those of 15/15 untrained controls.Contrasting with the expected, positive differences in most structural indicators observed between trained and untrained tibiae, trained fibulae had similar (distally) or smaller (proximally) cortical area, similar moments of inertia (MI, indicating bone stiffness) for anterior-posterior bending (xMI) and lower for lateral bending (yMI) with lower ?shape-index? (yMI/xMI ratio) throughout, and higher resistance to buckling (cortical thickness/bone diameter ratio) distally with respect to untrained bones. These differences, unrelated to bone mass, were more evident in men than women.Whilst greater stiffness and strength are typically thought to be advantageous for long bones, it may be that differences between the fibulae of runners and controls reflect alternative mechanical requirements of bone function. Proximally, the increased lateral flexibility of runners? fibulae (ability to store energy) could have contributed to fast-running optimization (which could represent a significant advantage for prey quadrupeds that are not too distant phylogenetically from humans). Distally, in spite of the general bone weakening revealed by the MI?s (convenient for heel-joint expansion, both in humans and in predator quadrupeds), buckling strength (critical to fracture) was larger in runners. To note, buckling is the most common cause of fracture of the distal fibula, and distal fibula is the most frequently fractured region in humans throughout the bone.This suggests that usage-derived strains in the fibula (and possibly other bones) may modify the relative structural resistance to different kinds of deformation in different regions, not only regarding strength, but also concerning other bone features which may show some critical selective connotation. This interpretation offers an original argument to propose a wider scope of bone mechanostat regulation of bone biomechanical features.