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Objective: To compare the bone temperature and final hole dimensions associated with sequential overdrilling (SO) and single 6.2-mm drill bit (S6.2DB) methods used to create transcortical holes in the third metacarpal bones (MCIIIs) of horse cadavers., Sample: 60 MCIIIs from 30 horse cadavers., Procedures: In phase 1, hole diameter, tap insertion torque, peak bone temperature, and postdrilling bit temperature for 6.2-mm-diameter holes drilled in the lateral or medial cortical region of 12 MCIIIs via each of three 2-bit SO methods with a single pilot hole (diameter, 3.2, 4.5, or 5.5 mm) and the S6.2DB method were compared. In phase 2, 6.2-mm-diameter transcortical holes were drilled via a 2-bit SO method (selected from phase 1), a 4-bit SO method, or a S6.2DB method at 1 of 3 locations in 48 MCIIIs; peak bone temperature during drilling, drill bit temperature immediately following drilling, and total drilling time were recorded for comparison., Results: Hole diameter or tap insertion torque did not differ among phase 1 groups. Mean ± SD maximum bone temperature increases at the cis and trans cortices were significantly less for the 4-bit SO method (3.64 ± 2.01°C and 8.58 ± 3.82°C, respectively), compared with the S6.2DB method (12.00 ± 7.07°C and 13.19 ± 7.41°C, respectively). Mean drilling time was significantly longer (142.9 ± 37.8 seconds) for the 4-bit SO method, compared with the S6.2DB method (49.7 ± 24.3 seconds)., Conclusions and Clinical Relevance: Compared with a S6.2DB method, use of a 4-bit SO method to drill transcortical holes in cadaveric equine MCIIIs resulted in smaller bone temperature increases without affecting hole accuracy.

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(o)C) than the uncoated pins (38.7 +/- 8.4(o)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.