Ex Vivo Pullout Strength of Locking and Cortical Screws in the Femur and Tibiotarsus of the Pekin Duck (Anas platyrhynchos domesticus)

The development of smaller orthopedic plates and screws has facilitated their use in avian fracture repair. Avian bone differs from mammalian bone in its biomechanical properties due to adaptations for flight, necessitating avian-specific orthopedic biomechanical studies. Screw pullout strength has not been studied in avian bone. The aims of this study were to 1) compare the axial pullout strength of cortical and locking screw designs in the tibiotarsus and femur of the Pekin duck (Anas platyrhynchos domesticus) and 2) investigate the effects of sex and screw location in bone on screw pullout strength. Locking and cortical screws were inserted in 5 locations: the distal metaphysis, distal diaphysis, middiaphysis, proximal diaphysis, and proximal metaphysis of femora (n = 28) and tibiotarsi (n = 40) from 20 Pekin ducks. Screws were tested to failure in axial pullout and maximum force recorded. Data were analyzed by a linear mixed-effects model. There were no significant differences in screw pullout strength between locking and cortical screws or between sexes. On average, maximum force was highest at the middiaphysis in the femur and at the distal diaphysis of the tibiotarsus. These results suggest that when using 2.0-mm and 1.5-mm screws in avian femoral and tibiotarsal bones, respectively, screw positioning in denser diaphyseal regions may be more critical to screw pullout strength than the choice between cortical and locking screw designs.