Structural differences in cortical shell properties between upper and lower human fibula as described by pQCT serial scans.A biomechanical interpretation.

GUSTAVO ROBERTO COINTRY; LAURA NOCCIOLINO; ALEX IRELAND; NICHOLAS HALL; ANDREAS KIERCHBAUMER; JOSÉ LUIS FERRETTI; JOERN RITTWEGER; RICARDO FRANCISCO CAPOZZA

BONE

ELSEVIER SCIENCE INC

Lugar: Amsterdam; Año: 2016 vol. 90 p. 185 - 194

8756-3282

This study describes the structural features of fibula cortical shell as allowed by serial pQCT scans in 10/10 healthymen and women aged 20?40 years. Indicators of cortical mass (mineral content -BMC-, cross-sectional area -CSA-), mineralization (volumetric BMD, vBMD), design (perimeters, thickness, moments of inertia -MIs-) andstrength (Bone Strength Indices, BSIs; polar Strength-Strain Index, pSSI) were determined. All cross-sectionalshapes and geometrical or strength indicators suggested a sequence of five different regions along the bone,which would be successively adapted to 1. transmit loads from the articular surface to the cortical shell (nearthe proximal tibia-fibular joint), 2. favor lateral bending (central part of upper half), 3. resist lateral bending(mid-diaphysis), 4. favor lateral bending again (central part of the lower half), and 5. resist bending/torsion (distalend). Cortical BMC and the cortical/total CSA ratio were higher at the midshaft than at both bone ends(p b 0.001). However, all MIs, BSIs and pSSI values and the endocortical perimeter/cortical CSA ratio (indicatorof the mechanostat's ability to re-distribute the available cortical mass) showed a ?W-shaped? distributionalong the bone, withmaximums at the mid-shaft and at both bone's ends (site effect, p b 0.001). The correlationcoefficient (r) of the relationship between MIs (y) and cortical vBMD (x) at each bone site (?distribution/quality?curve that describes the efficiency of distribution of the cortical tissue as a function of the local tissue stiffness)was higher at proximal than distal bone regions (p b 0.001). The results fromthe study suggest that human fibulais primarily adapted to resist bending and torsion rather than compression stresses, and that fibula's bendingstrength is lower at the center of its proximal and distal halves and higher at the mid-shaft and at both bone'sends. This would favor, proximally, the elastic absorption of energy by the attached muscles that rotate orevert the foot, and distally, the widening of the heel joint and the resistance to excessive lateral bending. Resultsalso suggest that biomechanical control of structural stiffness differs between proximal and distal fibula.