Study finds no implant edge in equine sesamoid fracture model: full analysis

CURRENT FULL VERSION: A new biomechanics paper adds evidence that a newer implant design may be viable, but not necessarily superior, for one of equine surgery’s more demanding fracture repairs. In Veterinary Surgery, researchers reported that a bone-screw-fastener and a conventional cortical buttress screw performed similarly in a simulated ex vivo model of medial mid-body proximal sesamoid bone fracture repair. What did stand out was configuration: two-screw constructs had significantly greater yield strength than single-screw constructs, regardless of implant type. (pubmed.ncbi.nlm.nih.gov)

The study comes out of Colorado State University’s Orthopedic Research Center, with collaborators in mechanical engineering and private equine practice. The project had earlier backing from the American College of Veterinary Surgeons Foundation, according to Colorado State’s orthopaedic research report, which listed the work as a comparison of the Osteocentric bone screw fastener and the AO buttress screw in this fracture model. That funding trail helps explain the longer development arc behind a paper that ultimately appeared online on November 25, 2025. (pubmed.ncbi.nlm.nih.gov)

In the experiment, the team created medial mid-body proximal sesamoid bone osteotomies in 14 paired equine cadaver forelimbs and repaired them using one of four constructs: a single 3.5 mm bone-screw-fastener, a single 4.5 mm cortical screw, two 3.5 mm bone-screw-fasteners, or two 3.5 mm cortical screws. Each group included seven repairs. On single-cycle-to-failure testing, the double bone-screw-fastener group reached a mean yield of 2081 ± 181 N, and the double cortical screw group reached 2101 ± 126 N. Both double-screw groups significantly outperformed the single-screw groups, which yielded at 1458 ± 92 N and 1532 ± 86 N, respectively. There were no significant differences between implant types within the single- or double-screw comparisons. The authors also found greater gap formation abaxially than axially at construct failure across all groups, pointing to persistent off-axis forces that may deserve more attention in repair planning. (pubmed.ncbi.nlm.nih.gov)

That last point fits with the broader history of proximal sesamoid fracture management. Earlier work has shown that screw fixation in lag fashion can outperform wire fixation clinically for mid-body proximal sesamoid fractures, largely because better reduction is associated with better outcomes. In a 25-horse retrospective series published in 2008, only 28% of horses raced after surgery overall, but horses treated with screw repair were more likely to return than those treated with wire fixation, and none of the horses with unimproved reduction raced. In other words, these fractures have long carried a guarded prognosis, and implant mechanics are only one part of the picture. (pubmed.ncbi.nlm.nih.gov)

There doesn’t appear to be much published third-party commentary yet on this specific sesamoid study, but the result is consistent with earlier veterinary research on bone-screw-fasteners in other settings. A 2023 Frontiers in Veterinary Science study of tibial plateau leveling osteotomy constructs in dogs likewise found similar biomechanical stability between bone-screw-fasteners and locking buttress screws under cyclic axial loading, rather than a clear advantage for the newer device. A similar theme shows up in other species and fixation models: in a feline ex vivo sacroiliac luxation model, investigators compared cannulated compression headless screws with cortical screws placed in positional or lag fashion and found no significant differences in total force, compression area, or total pressure under static testing. Those authors noted that the findings challenged the usual biomechanical rationale for favoring compression screws in that setting. Taken together, that suggests newer fastener or compression-oriented implants may broaden the toolkit without automatically improving construct performance. (pubmed.ncbi.nlm.nih.gov)

Why it matters: For veterinary professionals, especially equine surgeons, this is a useful reminder to focus on the mechanics that most affect stability. In this model, adding a second screw mattered more than switching from a conventional cortical screw to a bone-screw-fastener. That could influence implant selection, case planning, teaching, and conversations with pet parents about what a newer implant can and can’t promise. It also underscores a familiar translational gap: ex vivo strength data are helpful for screening techniques, but they don’t substitute for evidence on healing, anesthetic recovery, rehabilitation, cost, or return to athletic use. And the broader literature is pointing in the same direction: whether in equine sesamoid repair or feline sacroiliac fixation, newer screw designs may match standard implants biomechanically without clearly exceeding them. (pubmed.ncbi.nlm.nih.gov)

The findings may also be relevant beyond this one fracture type because they add to the veterinary orthopedics literature questioning whether newer compression or fastener designs automatically improve performance over established screws. That theme is echoed in other recent ex vivo work, including feline sacroiliac fixation research, where cannulated compression headless screws did not significantly outperform cortical positional or lag screws in interfragmentary compression. For clinicians, that’s a practical message: innovation may expand options, but evidence still has to show where it changes outcomes in real patients.

What to watch: Watch for cyclic-loading studies, live-horse clinical series, and any follow-up work on managing abaxial gap formation, because those data will be more informative than single-load bench testing when it comes to real-world prognosis and case selection. It will also be worth watching whether future comparative studies continue to challenge assumptions that compression-focused implants necessarily deliver superior biomechanics across species and fracture models. (pubmed.ncbi.nlm.nih.gov)