A biomechanical cadaveric analysis of polymethylmethacrylate-augmented pedicle screw fixation

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Instrumentation of the osteoporotic spine can be fraught with complications such as hardware failure. A cadaver study was performed to determine the biomechanical performance of polymethylmethacrylate (PMMA)–augmented pedicle screws.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Three osteoporotic human cadaveric specimens with a mean bone mineral density of 0.70 g/cm<jats:sup>2</jats:sup> were used to evaluate the performance of a novel fenestrated bone tap in pedicle screw augmentation. On this device, tap threads serve a dual purpose in preventing backflow of cement toward neural elements while allowing for a custom form for subsequent screw placement. The tap was used to inject a mean volume of 3.7 ml PMMA/pedicle (range 2–8.0 ml PMMA/pedicle) followed by pedicle screw placement between L-5 and T-5, alternating between augmented and nonaugmented instrumentation. Axial pullout testing was then performed.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Pedicle screw pullout strength was increased in both primary and salvage procedures by 119% (p = 0.001) and 162% (p = 0.01), respectively, after PMMA augmentation. Additionally, the injected cement volumes were divided into two groups, a low-cement group (≤ 2.8 ml/pedicle) and a high-cement group (≥ 5.5 ml/pedicle). Interestingly, the pullout strength did not significantly change with increased cement usage between the two groups (p &gt; 0.05 for all comparisons).</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Polymethylmethacrylate-augmented pedicle screw fixation results in a significant increase in the axial pullout strength of augmented pedicle screws in both primary and revision procedures. This technique may be a valuable adjunct in cases in which bolstering of the screw–bone interface is necessary.</jats:p></jats:sec>

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

“…9,22,24,32,36,44,48,49 The reason for high leakage rates in cadaver models might be the missing venous counter-pressure, 6 but this does not explain high leakage rates during surgery. The amount of applied cement in the literature varies between 1.8 ml and 2.9 ml per screw, 18,35 which is comparable to the amount used in the present study. Biomechanical capacity would not increase after raising the application above 2.8 ml per screw.…”

Polymethylmethacrylate-Augmented Screw Fixation for Stabilization of the Osteoporotic Spine : A Three-Year Follow-Up of 37 Patients

“…On the other hand, for Fransel et al's cases 14) , though only three patients were presented, 1.5 mL of PMMA was used in each patient and no extravasation of the bone cement occurred 14) . In addition, according to the cadaveric study of Frankel et al 12) , regarding the amount of PMMA injected into the vertebral body, the patients were divided into a "small-amount" group (≤ 2.8 mL/pedicle) and a "high-amount" group (≥ 5.5 mL/ pedicle). The pullout strength result for each group was similar, therefore, the authors recommended using lower amounts of cement for pedicle screw augmentation procedures 12) .…”

“…To compensate for the weaknesses inherent with the use of PMMA alone, novel cannulated pedicle screws have been designed and developed, its holes existing at the distal end of the screw. The biomechanical test results of these new kind of screws have been presented 12,22,37,45) . These screws are novel in their design and concept and clinical results after the use of one these screws are presented in the present paper.…”

Assessment of the Breakaway Torque at the Posterior Pelvic Ring in Human Cadavers

“…As a consequence, especially in the elderly, a very poor fixation was expected in the lateral mass of the sacrum [10]. The implant purchase may be enhanced by increasing the bone-implant contact area using modificated screws and techniques [7][8][9][10][11], or by the application of bone cement [12][13][14]. The use of cement-augmentation of standard iliosacral screws has been reported earlier [25], with promising preliminary outcomes noted when employing the use of iliosacral screws with perforations at the tip of the screws [26].…”

“…However, the diminished screw purchase of iliosacral screws as a monocortical screw device in cancellous, osteoporotic bone [5,6] does surpass the potential lack of compliance often seen with geriatric patients, particularly with regards to partial weight bearing. As a result, the purchase of iliosacral screws may be enhanced by increasing the bone-implant contact area using modified screws, techniques [7][8][9][10][11], and/or bone cement [12][13][14] to prevent loosening of hardware, especially in the osteopenic bone in the elderly. Therefore, the purpose of this study was to mechanically assess the local bone breakaway torque at various sites in the pathway of iliosacral screws used for fixation of the posterior pelvic ring by measuring peak breakaway torque in a human cadaveric model to determine the zones providing the weakest anchorage for fully-threaded iliosacral screws.…”