Revision characteristics of cement-augmented, cannulatedfenestrated pedicle screws in the osteoporotic vertebral body: a biomechanical in vitro investigation

Abstract

<jats:p>In generalized osteoporosis, instrumentation with cement-augmented pedicle screws is an amplification of the therapeutic spectrum. Early clinical results are promising for both solid and cannulated screws; however, there are concerns regarding the revision characteristics of these screws, especially for the cannulated-fenestrated type with its continuous cement interconnection from the core of the screw to surrounding bone tissue. In a human cadaver model, bone mineral density (BMD) was assessed radiographically. Spinal levels T9–L4 were instrumented left unilaterally, transpedicularly by using cannulated-fenestrated pedicle screws with the dimensions 6.5 × 45 mm. Polymethylmethacrylate cement (1.5 ml) was injected through the screws into each vertebra. After polymerization of the cement, the extraction torque was recorded. For both implantation and explantation of the screws, a fluoroscope was used to guarantee correct screw and cement positioning and to observe possible co-movements—that is, any movement of the cement mass within the vertebral body upon removal of the screw. For comparison, the extraction torque of same-dimension pedicle screws was recorded in a nonosteoporotic, non–cement-augmented instrumentation. The BMD was 0.60 g/cm<jats:sup>2</jats:sup>, a level that corresponds to a severe grade of osteoporosis. For removal of the screws, the median and mean extraction torques were 34 and 49 ± 44 Ncm, respectively. No co-movements of the cement mass occurred within the vertebral body. In the nonosteoporotic control, BMD was 1.38 g/cm<jats:sup>2</jats:sup>. The median and mean extraction torques were 123 and 124 ± 12 Ncm, respectively. Thus, the revision characteristics of cement-augmented, cannulated-fenestrated pedicle screws are not problematic, even in cases of severe osteoporosis. The winglike cement interconnection between the screw core and surrounding bone tissue is fragile enough to break off in the event of an extraction torque and to release the screw. There is no proof to support the theoretical fear that while trying to remove a screw, the composite of screw and cement would not break but instead would rotate as a whole in the osteoporotic vertebral body.</jats:p>

Pedicle Screw Design and Cement Augmentation in Osteoporotic Vertebrae

“…Higher-viscosity cements may also provide for safer screw augmentation by lowering the risk of inadvertent fl ow into the spinal canal or vascular system. [34][35][36] Use of higher-viscosity cement certainly did not come at any fi xation cost, as in our head-to-head comparison of Ffen screws with 2 different cements, the higher-viscosity cement demonstrated a trend toward higher failure loads than lowviscosity cement.…”

Cement leakage in pedicle screw augmentation: a prospective analysis of 98 patients and 474 augmented pedicle screws

“…33 Revision of cement-augmented pedicle screws can be done without hesitation, since it was practicable in the present study as well as in reports from the literature. 5,7 has the last word Been Said in cement augmentation?…”

A novel injectable calcium phosphate-based nanocomposite for the augmentation of cannulated pedicle-screw fixation

“…This complex can promote the mechanical stability of screw fixation, improve fatigue resistance, and also decrease the risk of cement leakage. [11][12][13] To date, all the clinical cases and most of the research have used only PMMA for the augmentation of cannulated screws, 14,15 largely due to the high fluidity and injectability of PMMA, which can easily be fed through a cannula of a typical diameter of 1.6 mm and outlet holes of small diameter -around 0.9 mm. Other types of bioabsorbable cements are comparatively less reported for applications in cannulated pedicle screws.…”