In vitro comparison of metaphyseal and diaphyseal placement of centrally threaded, positive-profile transfixation pins in the equine third metacarpal bone.

This research paper discusses an in-depth study conducted to compare the stability and possible structural damage resulting from placing central threaded, positive-profile transfixation pins either in the diaphysis or metaphysis of the horse’s third metacarpal bone.

Methodology

• The researchers utilized the third metacarpal bones from 30 pairs of adult horse cadavers.
• The transfixation pins were placed in the diaphysis of one bone, and the metaphysis of the opposite bone for 15 pairs of bones.
• The strength of each setup was then measured by determining the amount of tensile force each could withstand before breaking using a materials testing system.
• An additional set of 15 bone pairs were subjected to cyclic loading before testing.
• A further six pairs of bones were examined with scanning electron microscopy for microstructural damage under three different conditions: with tapped holes but without pin placements, after pin placements, and following pin placements and cyclic loading.
• The temperature of the hardware in 12 other metacarpal bones warmed to 38 C was also measured using a surface thermocouple.

Results

• The research found that the diaphysis provided a significantly higher resistance to axial extraction compared to the metaphysis.
• No significant temperature differences were observed between diaphyseal and metaphyseal placements.
• Microstructural damage was minimal, and only occasional microfractures were noticed in the cortical bone at both diaphyseal and metaphyseal locations.
• These microfractures occurred during the drilling and tapping process but did not increase following the placement of the transfixation pin or after cyclic loading.

Conclusion

• A conclusion was drawn from the study’s findings that centrally threaded, positive-profile transfixation pins have a higher resistance to axial extraction in the diaphysis than in the metaphysis of equine third metacarpal bone in vitro.
• This discovery could potentially lead to a more stable external skeletal fixation in horses with fractures.