COMPARATIVE STRUCTURAL ANALYSIS OF THE CANINE FEMORAL HEAD IN LEGG-CALVÉ-PERTHES DISEASE

The goal of this study was to examine the microarchitecture of the trabecular bone of the canine femoral head using microcomputed tomography (micro-CT) technology. Specifically, we assessed changes seen in the femoral head in dogs with Legg-Calvé-Perthes disease and compared this with changes seen in dogs with hip dysplasia and coxofemoral luxation. Femoral heads from healthy animals were examined as a control. In total, 38 femoral heads were studied. Rules for defining spherical volumes (region of interest) for determination of the structural parameters within the trabecular structure were established using micro-CT images. The following parameters were determined directly in three dimensions: bone volume fraction, surface volume fraction, trabecula thickness, trabecular count, trabecular spacing, and connectivity. Characteristic femoral head changes were found for each condition. An unexpected result was found that contradicts the prevailing understanding of Legg-Calvé-Perthes disease. Instead of observing a thickening of the bone trabeculae caused by layering of new bone matrix on top of necrotic trabeculae, we observed an increase in trabecular count and a smaller trabecular thickness. From this it may be concluded that trabecular regeneration is more prominent or prevails over the characteristically described layering processes in the revascularization and repair processes occurring in this illness.     

Investigating drivers of microbial activity and respiration in a forested bog

Northern peatlands store nearly one-third of terrestrial carbon(C)stocks while covering only 3%of the global landmass;nevertheless,the drivers of C cycling in these often-waterlogged ecosystems are different from those that control C dynamics in upland forested soils.To explore how multiple abiotic and biotic characteristics of bogs interact to shape microbial activity in a northern,forested bog,we added a labile C tracer(13C-labeled starch)to in situ peat mesocosms and correlated heterotrophic respiration with natural variation in several microbial predictor variables,such as enzyme activity and microbial biomass,as well as with a suite of abiotic variables and proximity to vascular plants aboveground.We found that peat moisture content was positively correlated with respiration and microbial activity,even when moisture levels exceeded total saturation,suggesting that access to organic matter substrates in drier environments may be limiting for microbial activity.Proximity to black spruce trees decreased total and labile heterotrophic respiration.This negative relationship may reflect the influence of tree evapotranspiration and peat shading effects;i.e.,microbial activity may decline as peat dries and cools near trees.Here,we isolated the response of heterotrophic respiration to explore the variation in,and interactions among,multiple abiotic and biotic drivers that influence microbial activity.This approach allowed us to reveal the relative influence of individual drivers on C respiration in these globally important C sinks.