Comparison of insertion characteristics of two types of hydroxyapatite-coated and uncoated positive profile transfixation pins in the third metacarpal bone of horses.

This research article studies the impact of two different types of hydroxyapatite coatings on transfixation pins used in horse’s bones. The comparison is made between the coated pins and the uncoated ones, focusing on the heat generated during the process and the required torque for insertion.

Methodology

• The researchers operated on the third metacarpal bone pairs from 27 cadaveric adult horses.
• Three types of pins were used: plasma-sprayed hydroxyapatite (PSHA)-coated, biomimetic hydroxyapatite (BMHA)-coated, and uncoated large animal transfixation pins.
• The peak temperature of the bone where the pin was inserted and the pin itself was measured. These measurements were taken at both the cis-cortex (closer to the center) and the trans-cortex (outer edge) of the bone.
• The torque needed to insert each pin was also recorded.
• Finally, they visually and microscopically evaluated the bone-pin interface to assess the level of damage that the bone and the coating had suffered.

Results

• BMHA-coated pins had similar insertion characteristics to uncoated pins.
• PSHA-coated pins, on the other hand, raised the bone temperatures to higher values than both BMHA-coated and uncoated pins.
• The PSHA-coated pin on the trans-cortex heated to 70.9 +/- 6.4 degrees Celsius, while the uncoated pins only heated to 38.7 +/- 8.4 degrees Celsius.
• The PSHA-coated pins also required more torque for insertion.
• Additionally, four of the PSHA-coated pins became immovable once fully inserted, and one pin created a gross fracture during its insertion.

Conclusions

• The researchers concluded that while BMHA-coated pins had a comparable performance to the uncoated pins, the PSHA-coated pins had a lower performance due to their higher heat generation, additional torque requirement, and other negative effects such as immovability and risk of fracturing the bone.
• They stated that it would not be feasible to employ PSHA coating without making changes in the existing pin hardware.
• Finally, they recommended further testing on BMHA-coated pins, particularly in live horse models, to better ascertain their ability to integrate with equine bone (“osteointegration”).