Biomechanical Comparison of “Headless Compression Screw Fasteners” and Cortical Bone Screws for Fixation of Equine Third Carpal Bone Fractures. Salinger A1, Mochal-King C1, Priddy L2, Elder S2, Jaffe M1. 1Mississippi State University, College of Veterinary Medicine, Mississippi State, MS; 2Mississippi State University, College of Agricultural & Biological Engineering, Mississippi State, MS.
Frontal plane slab fractures of the radial facet account for the majority of third carpal bone (C3) fracture types in racehorses. A novel, cannulated screw with interlocking threads (“Headless Compression Screw Fastener,” HCSF) was investigated for C3 fracture repair. The objective of this study is to compare the maximal shear compressing force to failure of a HCSF to an AO cortical bone screw. The left or right carpi of eight pairs of cadaver limbs were randomly assigned for fixation of a simulated radial facet frontal plane slab fracture with either the 3.9 mm HCSF (Group F) or 3.5 mm AO cortical bone screw (Group C). Shear force was applied across the fracture line, and a load cell measured the force. Average maximal load to failure of Groups F and C were 2787.914 N ± 1693.711 and 3089.07 N ± 845.387, respectively. Average stiffness was 433.415 N/mm ± 213.783 and 449.371 N/mm ± 134.063, respectively. Biomechanical performance was comparable. HCSF may have benefits, including the headless component obviating the need to countersink and eliminating dorsal soft tissue irritation. The cutting and interlocking threads may prevent fragment splitting and spinning. A limitation of the study was due to its ex vivo nature, being unable to account for all forces associated with C3 slab fractures. The results of this study indicate that the HCSF can be successfully placed in the equine C3 and performs comparably to cortical screws tested in shear. These results invite clinical application to be further investigated.