Characteristics of pelvic limb long bones in 14-year-old female emu (Dromaius novaehollandiae)

Investigation of morphological, geometric, densitometric, and mechanical properties of femur, tibiotarsus, tarsometatarsus, and libula in 14-year-old female emu was performed. Densitometric measurements were executed using dual energy X-ray absorptiometry and quantitative computed tomography. Geometric properties of femur and tibiotarsus were determined. Mechanical evaluation was performed using three-point bending test. Bone weight, relative bone weight, bone length, and total bone volume were differentiated between all the evaluated bones. The size of femur was relatively small in relation to tibiotarsus and tarsometatarsus as expressed by its weight, total bone volume, and percentage contribution to final body weight. Volumetric bone mineral density values measured manually for trabecular and cortical bone compartments were significantly higher in tibiotarsus and tarsometatarsus than in femur, withstanding lower physiologcal loading (P<0.01). The values of trabecular bone mineral density of distal tibiotarsus and proximal tarsometatarsus were not significantly different (P=0.70), but they were significantly higher than in proximal and distal femur (P<0.05). Manually determined cortical bone area of tibiotarsus and tarsometatarsus were significantly lower than that of femur (P<0.05). Maximum elastic strength and ultimate strength were the highest in tarsometatarsus, then in tibiotarsus and in femur, and the lowest in fibula (all P<0.05). Functional adaptation of body weight bearing bones of pelvic limb in emu to withstand heavier loading is expressed by the highest mechanical endurance in tarsometatarsus then in tibiotarsus and the lowest in femur. Although similar location in pelvic limb bone array, body weight non-bearing fibula showed 50-60 times lower mechanical endurance than tibiotarsus.