Original evidence of a different adaptation of proximal and distal cortical shell of the human fibula to the bone?s mechanical environment.

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

Atlanta (Georgia)

Congreso; XXXVIII ANNUAL MEETING, American Society for Bone & Mineral Research; 2016

American Society for Bone & Mineral Research.

Ina previous study we had shown a different response of human tibia and fibulacortical structure to disuse. This finding led us to analyze the corticalstructure of the normal human fibula from a biomechanical point of view. Withthat purpose, we took serial pQCT scans at every 5% of the fibula lengthcomprised between the tibio-tarsal joint line and the proximal articularsurface of the tibia (19 scans per individual) of 10/10 healthy, sedentary menand women aged 20-40 years. Indicators of fibula cortical mass (BMC,cross-sectional area -CSA-), mineralization (vBMD), design (perimeters, momentsof inertia -MIs-) and strength (Bone Strength Indices, BSIs; Strength-StrainIndex, SSI) were determined. Allcross-sectional shapes and geometrical/strength indicators suggested a sequenceof five different regions along the bone, which would be successively adaptedto 1. transmit loads from the articular surface to the cortical shell (close tofibula-tibia upper joint), 2. favor lateral bending (central part of upperhalf), 3. resist lateral bending (mid-diaphysis), 4. favor lateral bendingagain (central part of the lower half), and 5. resist bending/torsion (distalend). Cortical BMC and the cortical/total CSA ratio were higher at the midshaftthan at both bone ends (p<0.001). However, all MIs, BSIs and SSI values andthe endocortical perimeter/cortical CSA ratio (indicator of the mechanostat?s ability to re-distributethe available cortical mass) showed a ?W-shaped? distribution along the bone,with maximums at the mid-shaft and at both bone?s ends (p<0.001). Thecorrelations between MIs (y) and cortical vBMD (x) at each bone site(?distribution/quality? curves that describe the efficiency of distribution ofthe cortical tissue as a function of the local tissue stiffness) showed higher rcoefficients at proximal than distal bone regions (p<0.001). Resultsshow that 1. human fibula is primarily adapted to resist bending and torsionrather than compression, and 2. fibula?s bending strength is lower at thecenter of its proximal and distal halves and higher at the mid-shaft and atboth bone´s ends. This would a. favor, proximally, the elastic absorption ofenergy by the attached muscles that rotate/evert the foot, and distally, thewidening of the heel joint and the resistance to excessive lateral bending, andb. suggest that biomechanical control of structural stiffness differs betweenproximal and distal fibula.