A COMPARISON OF THE SYNTHES 4.5-MM CANNULATED SCREW AND THE SYNTHES 4.5-MM STANDARD CORTEX SCREW SYSTEMS IN EQUINE BONE

Objective-To determine risk of failure of the Synthes 4.5-mm cannulate d screw system instrumentation in equine bone and to compare its appli cation with the Synthes 4.5-mm standard cortex screw system. Study Des ign-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 cannulate d and standard cortex screws were also determined. Sample Population-P aired equine cadaver third metacarpal and third carpal bones. Methods- Maximum insertion torque and ultimate torsional strengths were determi ned by using an axial-torsional, servohydraulic materials testing syst em and a hand-held torquomater. Pullout tests were performed by using a servohydraulic materials testing system. Results-Maximum insertion t orque of all cannulated instrumentation was less than ultimate torsion al strength at all locations (P < .05). Maximum insertion torques of c annulated taps and screws were greater than for standard taps and scre ws in the third carpal bone (P < .002). Pullout strength of the cannul ated screws was less than the standard cortex screws at all sites (P < .001). Cannulated screws broke before bone failure in all but one bon e specimen. Conclusions-The risk of cannulated instrument or screw fai lure during insertion into bone is theoretically low. The relatively l ow pullout strength of the cannulated screws implies that the interfra gmentary compression achievable is likely to be less than with standar d cortex screws. Clinical Relevance-The relatively low pullout strengt h of the cannulated screw suggests that its risk of failure during fra cture repair is greater than with the standard cortex screw. (C) Copyr ight 1998 by The American College of Veterinary Surgeons.