293. Biomechanical assessment of pedicle screw fixation strength in nonosteoporotic and osteoporotic pedicles: comparison of straight dual-lead vs single- to dual-lead threadforms

Abstract

BACKGROUND CONTEXT Pedicle screw loosening occurs in 1-21% of patients at 3 to 6 months postoperative and can lead to construct instability. Loosening has been attributed to screw insertion technique, interbody device subsidence, and compromised bone quality. Screw threadform design aims to maximize screw purchase over the spectrum of bone quality to provide superior fixation strength, resistance to loosening and ease of insertion. Single- to dual-lead threadforms aim to provide increased fixation in dense cortical bone, but its single-lead thread provides no advantage in insertion time. Straight dual-lead threadforms provide uniform pitch over the length of the screw and have inherently decreased insertion times compared to those of single-lead screws. The objective of this study was to biomechanically assess the anchoring capacity of straight dual-lead and single- to dual-lead threadforms in axial pullout and cyclic toggle to failure, the most clinically relevant mode of pedicle screw loosening. We hypothesize both threadform designs will yield equivalent anchoring capacity, and that anchoring capacity will be greater in non-osteoporotic vs osteoporotic bone. METHODS Two pedicle screw designs, a straight dual-lead pedicle screw and a single- to dual-lead pedicle screw, of equal length (45mm) and equal outer diameter (6.5mm) were biomechanically tested in axial pullout and cyclic toggle to failure. Nonosteoporotic (n=16, BMD>0.80g/cm2) and osteoporotic (n=16, BMD RESULTS Neither peak load during axial pullout nor failure load during cyclic toggle were significantly different (p>0.05) between threadforms in either bone quality group. Both threadforms yielded significantly larger peak (p CONCLUSIONS Straight dual-lead and single- to dual-lead threadforms yield statistically equivalent anchoring capacity within pedicles of both non-osteoporotic and osteoporotic vertebrae under non-clinical biomechanical test conditions.Time of insertion may be of consideration given equivalent anchoring capacity. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.