A biomechanical comparison of headless tapered variable pitch compression and ao cortical bone screws for fixation of a simulated midbody transverse fracture of the proximal sesamoid bone in horses.

The research explores the mechanical properties and failure characteristics of two methods used for repairing a specific kind of fracture in horses. The study concludes both methods are mechanically comparable, but suggests the Acutrak screw due to potential benefits like less soft tissue impingement and better biocompatibility.

Objective of the Study

• The primary objective of this study was to compare the effectiveness of two different fixation methods used for the repair of a transverse, midbody fracture of the proximal sesamoid bone in horses. The fixation tools compared were a 4.5-mm AO cortical bone screw placed in lag fashion and a 4/5-mm Acutrak self-compressing screw.

Methods Used

• In the biomechanical evaluation, researchers used sixteen paired and eight unilateral cadaveric equine forelimbs. A midbody transverse osteotomy was created in the medial PSB of bilateral forelimbs from eight equine cadavers.
• One forelimb from each cadaver was repaired using the AO screw, while the contralateral limb was repaired using an AT screw. Eight unilateral intact control limbs were also studied.
• The team then assessed the mechanical properties from axial compression, single cycle to failure, and load-deformation curves. Failure characteristics were determined by evaluating video images and radiographs.

Results

• The results showed that there were no significant differences between the groups repaired with either the AO or AT screws. However, both groups demonstrated significantly lower mechanical properties than the intact limbs, apart from stiffness.

Conclusion and Clinical Relevance

• The research concluded that the AO and AT constructs were mechanically similar when used to stabilize a simulated midbody fracture of the medial PSB. However, they were mechanically inferior to intact limbs.
• In a clinical setting, the study suggests considering the AT screw for clinical use due to potential advantages such as less soft tissue impingement and better biocompatibility compared to the stainless-steel AO screw.
• To augment initial fracture stability for either fixation method, the study recommends postoperative external coaptation. It also suggests maintaining a standing metacarpophalangeal joint dorsiflexion angle between 150-155 degrees.