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

Abstract

Objective - To determine the effect of 2 hydroxyapatite pin coatings on heat generated at the bone-pin interface and torque required for insertion of transfixation pins into cadaveric equine third metacarpal bone. Sample Population - Third metacarpal bone pairs from 27 cadavers of adult horses. Procedures - Peak temperature of the bone at the cis-cortex and the hardware and pin at the trans-cortex was measured during insertion of a plasma-sprayed hydroxyapatite (PSHA)-coated, biomimetic hydroxyapatite (BMHA)-coated, or uncoated large animal transfixation pin. End-insertional torque was measured for each pin. The bone-pin interface was examined grossly and histologically for damage to the bone and coating. Results - The BMHA-coated transfixation pins had similar insertion characteristics to uncoated pins. The PSHA-coated pins had greater mean peak bone temperature at the cis-cortex and greater peak temperature at the trans-cortex (70.9 ± 6.4°C) than the uncoated pins (38.7 ± 8.4°C). The PSHA-coated pins required more insertional torque (10,380 ± 5,387.8 Nmm) than the BMHA-coated pins (5,123.3 ± 2,296.9 Nmm). Four of the PSHA-coated pins became immovable after full insertion, and 1 gross fracture occurred during insertion of this type of pin. Conclusions and Clinical Relevance - The PSHA coating was not feasible for use without modification of presently available pin hardware. The BMHA-coated pins performed similarly to uncoated pins. Further testing is required in an in vivo model to determine the extent of osteointegration associated with the BMHA-coated pins in equine bone.