Experimental Surgeon, Project Leader AO Foundation - Research Institute Davos Platz, Switzerland
Improved Biomechanical Properties of Modified 5.5 mm Cortex Screw with Larger Head Size in an Equine Lateral Condylar Fracture Model. Constant C, Zderic I, Arens D, Pugliese B, Gehweiler D, Gueorguiev-Rüegg B, Zeiter S. AO Research Institute, Davos Platz, Switzerland.
The 5.5 mm large animal cortex screw was created with the same head diameter as the 4.5 mm cortex screw, which could reduce the full potential of this implant by undermining its ability to produce interfragmentary compression. Therefore, this study compared modified 5.5 mm cortex screw inhering a larger head diameter versus standard 5.5 mm cortex screw in an equine condylar fracture model. Fifteen pairs of equine third metacarpal (MC3) bones underwent lateral condylar fractures creation by parasagittal osteotomies and were repaired pairwise with modified or standard 5.5 mm cortex screws. Interfragmentary compression at maximum screw insertion torque was measured before the specimens were pairwise stratified for biomechanical testing under the following modalities (n = 5): 1) torque to failure, 2) quasi-static axial load to failure, and 3) cyclic axial load to failure. Tests 1 and 2 were respectively analyzed for yield, maximum and failure torque, angle and load. Number of cycles to 2 mm displacement was assessed from test 3. Maximum insertion torque was greater and failure angle smaller for modified screw (8.1 ± 0.5 vs. 7.4 ± 0.5 Nm; P = 0.0047 and 1130° ± 230° vs. 550° ± 104°; P = 0.008). Axial failure load (12347 ± 3359 vs. 8695 ± 2277 N, P = 0.043) and yield load (7118 ± 707 vs. 5740 ± 2267 N, P = 0.043) were greater for specimens repaired with modified screw. Number of cycles to 2 mm displacement was greater, but not statistically significant for modified screw (85907 ± 154966 vs. 26618 ± 58056 cycles). In conclusion, modified 5.5 mm cortex screws to repair condylar MC3 fractures showed increased maximal hand torque insertion, decreased failure angle, and increased by 1.4-fold quasi-static failure forces compared with standard 5.5 mm screws.