A biomechanical and histological analysis of standard versus hydroxyapatite-coated pins for external fixation

This sheep study was designed to make a comparative evaluation of two external fixation pin types each with and without hydroxyapatite (HA) coating. The two pins had different taper, pitch, and self drilling capabilities. Twenty Orthofix standard, self‐tapping pins (group A), 20 Orthofix HA‐coated, self‐tapping pins (group B), 20 X‐caliber, self‐drilling, self‐tapping pins (group C), and 20 X‐caliber HA‐coated, self‐drilling, self‐tapping pins (group D) were selected. Four pins were implanted in the right femurs of 20 adult sheep that were euthanized at 6 weeks. Mean pin insertion torque was 2745 ± 822 Nmm in group A, 2726 ± 784 Nmm in group B, 2818 ± 552 Nmm in group C, and 2657 ± 732 Nmm in group D (ns). Mean pin extraction torque was 1567 ± 541 Nmm in group A, 2524 ± 838 Nmm in group B, 1650 ± 650 Nmm in group C, and 2517 ± 726 Nmm in group D. HA‐coated pins (group B and D) had a significantly greater mean pin extraction torque compared to similar uncoated pins (group A and C) (p < 0.0005). Histological analysis showed good osteointegration of the two coated pin types. This study shows that HA‐coating is more important for optimal pin fixation than the particular combination of design parameters used in each pin type. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008