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A Comparison of the Synthes 4.5-mm Cannulated Screw and the Synthes 4.5-mm Standard Cortex Screw Systems in Equine Bone |
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| Authors: | SALLY A COLGAN BVSc AARON T HECKER MS CARL A KIRKER-HEAD MA Vet MB MRCVS Diplomate ACVS Diplomate ECVS WILSON C HAYES PhD |
| Institution: | Orthopaedic Research Laboratory, Tufts University School of Veterinary Medicine, North Grafton, MA;the Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Charles A. Dana Research Institute, Harvard Thorndike Laboratory, Beth Israel Hospital;and Harvard Medical School, Boston MA. |
| Abstract: | Objective —To determine risk of failure of the Synthes 4.5-mm cannulated screw system instrumentation in equine bone and to compare its application with the Synthes 4.5-mm standard cortex screw system. Study Design —The maximum insertion torque of the cannulated and standard cortex screw systems were compared with the ultimate torsional strengths of the equipment. Pullout strength and ultimate tensile load of cannulated and standard cortex screws were also determined. Sample Population—Paired equine cadaver third metacarpal and third carpal bones. Methods —Maximum insertion torque and ultimate torsional strengths were determined by using an axial-torsional, servohydraulic materials testing system and a hand-held torquometer. Pullout tests were performed by using a servohydraulic materials testing system. Results —Maximum insertion torque of all cannulated instrumentation was less than ultimate torsional strength at all locations ( P < .05). Maximum insertion torques of cannulated taps and screws were greater than for standard taps and screws in the third carpal bone ( P < .002). Pullout strength of the cannulated screws was less than the standard cortex screws at all sites ( P < .001). Cannulated screws broke before bone failure in all but one bone specimen. Conclusions—The risk of cannulated instrument or screw failure during insertion into bone is theoretically low. The relatively low pullout strength of the cannulated screws implies that the interfragmentary compression achievable is likely to be less than with standard cortex screws. Clinical Relevance—The relatively low pullout strength of the cannulated screw suggests that its risk of failure during fracture repair is greater than with the standard cortex screw. |
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