A pilot in vitro biomechanical comparison of locking compression plate fixation and kerf cut cylinder fixation for ventral fusion of fourth and fifth equine cervical vertebrae

Introduction: The mechanical properties of equine cervical vertebrae joined by implants have not yet been reported. Locking compression plates (LCP) may provide a useful alternative system to the commonly used stainless steel kerf-cut cylinders (KCC) currently used for fixation of cervical vertebrae in horses. Objectives: The objectives of this study were to establish a method for biomechanical testing of equine C4-C5 articulations and to compare the biomechanical properties of cadaveric spines stabilised with KCC and LCP. Methods: Twenty-four equine cadaveric cervical spines were size measured from radiographs, and then randomly allocated to four groups. The C4-C5 articulation for each group was treated in the following way: group 1: KCC implanted, group 2: 8-hole 4.5/5.0 LCP implanted, group 3: 11-hole 3.5 LCP implanted and group 4: No implant. The specimens were fixed in resin and tested under four-point bending in ventral flexion until failure. Stiffness, maximum moment to failure and mode of failure were recorded for all specimens. General linear models were performed to analyse associations. Results: All spines failed at the C4-C5 articulation. Failure however differed between groups with fractures in group 1, screw pull-out in groups 2 and 3, and disarticulation in group 4 being the common failure modes. The stiffness and maximum moment to failure of the KCC and LCP implanted spines were similar. Increasing age was significantly associated with decreasing moment to failure and increasing size was significantly associated with increasing moment to failure and stiffness. Clinical significance: This study describes a successful technique for examining the biomechanical properties of equine cervical vertebrae. The LCP constructs had similar mechanical properties to the KCC which may justify their use in clinical cases.