A Biomechanical Comparison of Headless Tapered Variable Pitch and AO Cortical Bone Screws for Fixation of a Simulated Slab Fracture in Equine Third Carpal Bones

Abstract

Considering the comparable mechanical behavior, greater initial shear stiffness for AT screw stabilized C3 slab fracture fragments, the ability to accurately insert the screw with the aid of a guide pin, and the potential for less persistent soft tissue irritation with the headless screw design, the 4/5 tapered AT screw is an attractive alternative for repair of C3 slab fractures in horses.

Clinical Evaluation of a Titanium, Headless Variable‐Pitched Tapered Cannulated Compression Screw for Repair of Frontal Plane Slab Fractures of the Third Carpal Bone in Thoroughbred Racehorses

“…These characteristics facilitate accurate screw placement, prevent the need for countersinking, decrease the possibility of fragment splitting, and eliminate screw head impingement on dorsal soft tissues, while achieving stable fixation. In vitro, simulated frontal plane C3 slab fractures repaired with either 4.5 mm AO cortical or 4/5 AT compression screws had comparable mechanical shear testing variables 14 suggesting that the AT screw system would likely meet the loading environment for C3 slab fracture fixation in vivo. In the current study, we repaired 17 C3 slab fractures using the AT screw system with minimal surgical complications.…”

“…The Acutrak ® (AT) screw is a titanium alloy, cannulated, headless, variable pitch, self‐tapping, tapered compression screw (Acumed, Beaverton, OR). The AT screw was designed for various orthopedic disorders in humans including fracture fixation and arthrodesis of the hand and foot, fixation of osteochondral fragments, stabilization of osteotomies, and repair of acute nonunion scaphoid fractures 14 . Like the Herbert screw, the AT screw is cannulated which facilitates accurate placement over a guide pin and helps maintain adequate fracture reduction during drilling, tapping, and screw implantation 8 …”

“…The headless design allows the screw to be positioned beneath the outer cortex which prevents impingement on the overlying tendons, joint capsule, or periosteum and eliminates the need for countersinking in larger fracture fragments 8,14–17 . This design also decreases the likelihood of fragment splitting because there is no screw head applying compression to the fracture fragment 8,14 . Finally, the AT screw is composed of titanium alloy which is more biocompatible than stainless steel and elicits less tissue reaction 20…”

“…Despite these potential advantages, it is unknown whether the AT screw can meet the demands of the loading environment required for repair of equine C3 fractures. To address this question before evaluating the AT screw type in vivo, an in vitro monotonic biomechanical study of simulated third carpal bone slab fractures repaired with either 4.5‐mm AO cortical (AO) or 4/5 AT compression screw was performed 14 . We found that insertion variables such as drilling torque, tapping (AO) versus screw insertion (AT) torque, and maximum screw torque were comparable between screw types.…”

“…Our objective was to describe a surgical technique for AT placement and to report results after repair of frontal plane C3 slab fractures in Thoroughbred racehorses. Based on previous in vitro biomechanical testing results, 14 we hypothesized that a headless titanium, tapered, cannulated, compression screw would provide sufficient compression and holding strength to stabilize C3 frontal plane slab fractures in Thoroughbred racehorses. To test this we prospectively enrolled Thoroughbred racehorses with C3 frontal plane slab fractures admitted to our practices between 1999 and 2004 for fracture repair using the AT system and assessed outcome, especially racing performance (starts, earnings).…”