Evaluation of XXXX paste for augmentation of lumbar pedicle screw pullout strength.

@entity4625 @entity77
BACKGROUND CONTEXT: Many authors have evaluated the components responsible for ultimate pullout strength of pedicle screws. In these studies, one important variable has been the screw fixation. Because pedicle screw fixation has increased in popularity over recent years, so has the need for augmentation in difficult situations. @entity4625 ( @entity4625 ) has been established as the gold standard in terms of strength of fixation but has the potential for severe complications when applied in spine surgery. @entity77 is an alternative to @entity4625 , because it lacks the exothermic reaction, is potentially osteoconductive and is resorbed by the body in 30 to 60 days. PURPOSE: To determine the strength of a new @entity77 cement in terms of pedicle screw augmentation. The purpose was to evaluate @entity77 versus @entity4625 in terms of pullout strength. @entity4625 was considered the gold standard in terms of strength for this experiment. STUDY DESIGN: Lumbar vertebrae implanted with pedicle screws were subjected to axial pullout tests. The force required to cause implant failure was measured and compared for three methods of fixation. OUTCOME MEASURES: Force to failure (Newtons) for each pedicle test was recorded and analyzed with results from similarly augmented pedicles. METHODS: Lumbar vertebrae were harvested from four cadavers and implanted with pedicle screws. These screws were either placed in native bone or augmented with either @entity77 paste or @entity4625 . In those pedicles that had augmentation, the material was permitted to set for a minimum of 24 hours. Axial pullout tests were then performed using an MTS (Materials Testing System Corporation, Minneapolis, MN) testing machine. The screws were pulled out over a distance of up to 6 mm at 0.25 mm/sec. This rate and distance ensured failure in each case. The load to failure was recorded for each pedicle. RESULTS: @entity77 augmentation improved pedicle screw pullout strength significantly when compared with native bone (p=.0003). This represented an average increase of 167% over the native bone. Likewise, @entity4625 improved the pullout strength significantly over native bone (p<.0001) for an average increase of 199%. There were no significant differences between the @entity77 and @entity4625 augmentation (p=.0791), although the @entity4625 averaged 119% of the strength of @entity77 . CONCLUSIONS: Although @entity4625 is considered the gold standard in terms of fixation strength, its use around the spine has been limited because of concern over complications. The @entity77 bone paste tested in this study demonstrated strength similar to @entity4625 without the major risks to the spinal cord. In addition, the @entity77 paste allows for possible osteoconduction to aid in spinal fusion. Further study is needed to determine the applicability of this @entity77 paste in the clinical setting of spine surgery.
