HERNANDEZ, E.*; O’CONNOR, P.M.; FAJARDO, R.J.; Beth Israel Deaconess Medical Center- Boston MA; Ohio University College of Osteopathic Medicine- Athens, OH; Harvard Medical School and Beth Israel Deaconess Medical Center- Boston, MA: MicroCT Analysis of the Axial Postcranial Skeleton in Birds: Comparison of Centrum Bone Structure in Two Anatids with Different Pneumatic States
Many extant birds possess an air filled postcranial skeleton. This condition results from invasion of epithelial expansions from the pulmonary air sacs. Anseriform birds exhibit marked interspecific variability in the extent of this postcranial pneumatization. A The long bones of these species have been characterized as exhibiting reductions of trabecular bone, thinner cortices, and decreased bending strength. It is unclear if these skeletal traits generalize to other parts of the skeleton. The axial skeleton is also pneumatized in many species. This study examined the structural differences between pneumatic and apneumatic avian centra. Twelve third thoracic centrum specimens of two anatids (7 Aix sponsa-pneumatic, 5 Oxyura jamaicensis-apneumatic) of comparable body size, but differing pneumaticity states were microCT scanned. Bone structural parameters were evaluated including the bone volume fraction, trabecular thickness, trabecular number, and the degree of anisotropy. T-tests were used to compare the means of the two groups . Results indicated that the whole centrum bone volume fraction differed significantly between A. sponsa and O. jamaicensis (A. sponsa=.346, O. jamaicensis=.450, p < 0.05). However, the bone volume fractions of the centra�s endosteal cavities were similar. No other differences were found between the species in the trabecular thickness, trabecular number, and degree of anisotropy of the endosteal cavity. This study showed that the centrum of O. jamaicensis has relatively more bone than that of A. sponsa, but both species have similar amounts of trabecular bone. These results suggest that O. jamaicensis has more cortical bone in the centrum�s than A. sponsa. It is unclear if these differences will translate into actual differences in the compressive properties of these species� vertebral centra. This study found no support for those observations that the presence of the epithelium inside bones displaces the trabeculae.
