Biomechanical comparison of compact versus standard flute drill bits, and interlocking versus buttress thread self-tapping cortical bone screws in cadaveric equine third metacarpal condyle.
Authors: Pye Jannah L, Garcia Tanya C, Kapatkin Amy S, Samol Monika A, Stover Susan
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: Interlocking versus Buttress Thread Screws in Equine Metacarpal Fracture Repair Selecting the optimal screw design for equine fracture fixation requires understanding how different thread geometries and drilling techniques interact with bone biomechanics. Researchers from UC Davis tested paired third metacarpi from young Thoroughbreds, systematically inserting both interlocking thread (ITS) and buttress thread (BTS) self-tapping screws into the lateral condylar fossae using either compact or standard flute drill bits, then measured insertion properties and pullout resistance alongside microcomputed tomography analysis of bone density and porosity. Whilst ITS demonstrated 50% higher insertion torque—suggesting superior initial bone engagement—BTS exhibited substantially greater resistance to axial pullout forces, with 33% greater preyield stiffness and 7% higher mean yield force. For fracture repairs subjected to predominantly tensile loading, BTS appears biomechanically superior, making ITS selection difficult to justify clinically despite its insertional advantages. These findings have direct implications for surgical planning in condylar fractures and other high-load metacarpal injuries, where pullout resistance rather than insertion torque should drive screw selection.
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Practical Takeaways
- •For equine metacarpal fracture repair, buttress thread screws are biomechanically superior to interlocking thread screws when axial pullout forces are expected—use BTS for tensile-loading situations.
- •Compact flute drill bits may outlast standard flute bits in clinical use due to reduced torque oscillation during drilling.
- •Bone quality around the screw hole site significantly influences fixation success regardless of screw or drill type selected; consider bone density when planning surgical approach.
Key Findings
- •Compact flute drill bits produced lower maximum torque power spectral density compared to standard flute bits, potentially improving drill durability.
- •Interlocking thread screws (ITS) required 50% higher insertion torque than buttress thread screws (BTS), indicating greater bone engagement.
- •Buttress thread screws demonstrated 33% greater preyield stiffness and 7% greater mean yield force compared to interlocking thread screws.
- •Bone tissue properties (density and porosity) similarly affected drilling and screw performance outcomes for both screw and drill bit types.