Pull-out strength of cemented solidversusfenestrated pedicle screws in osteoporotic vertebrae

Abstract

ObjectivesCement augmentation of pedicle screws could be used to improve screw stability, especially in osteoporotic vertebrae. However, little is known concerning the influence of different screw types and amount of cement applied. Therefore, the aim of this biomechanical in vitro study was to evaluate the effect of cement augmentation on the screw pull-out force in osteoporotic vertebrae, comparing different pedicle screws (solid and fenestrated) and cement volumes (0 mL, 1 mL or 3 mL).Materials and MethodsA total of 54 osteoporotic human cadaver thoracic and lumbar vertebrae were instrumented with pedicle screws (uncemented, solid cemented or fenestrated cemented) and augmented with high-viscosity PMMA cement (0 mL, 1 mL or 3 mL). The insertion torque and bone mineral density were determined. Radiographs and CT scans were undertaken to evaluate cement distribution and cement leakage. Pull-out testing was performed with a material testing machine to measure failure load and stiffness. The paired t-test was used to compare the two screws within each vertebra.ResultsMean failure load was significantly greater for fenestrated cemented screws (+622 N; p ⩽ 0.001) and solid cemented screws (+460 N; p ⩽ 0.001) than for uncemented screws. There was no significant difference between the solid and fenestrated cemented screws (p = 0.5). In the lower thoracic vertebrae, 1 mL cement was enough to significantly increase failure load, while 3 mL led to further significant improvement in the upper thoracic, lower thoracic and lumbar regions.ConclusionConventional, solid pedicle screws augmented with high-viscosity cement provided comparable screw stability in pull-out testing to that of sophisticated and more expensive fenestrated screws. In terms of cement volume, we recommend the use of at least 1 mL in the thoracic and 3 mL in the lumbar spine.Cite this article: C. I. Leichtle, A. Lorenz, S. Rothstock, J. Happel, F. Walter, T. Shiozawa, U. G. Leichtle. Pull-out strength of cemented solid versus fenestrated pedicle screws in osteoporotic vertebrae. Bone Joint Res 2016;5:419–426.

Pull out Strength of Dual Outer Diameter Pedicle Screws Compared to Uncemented and Cemented Standard Pedicle Screws: A Biomechanical in vitro Study

“…In this case, the screws were removed again after initial placement and reimplanted after cement injection. According to our previous findings, 1 mL of cement was used in the thoracic and 3 mL in the lumbar vertebrae. Prior to mechanical testing, the cement was allowed to harden at room temperature for at least 12 h. CT scans were performed to document proper screw position.…”

“…Mechanical pull‐out testing was performed using a material testing machine (MTS 858 Mini Bionix, Eden Prairie, MN, USA) equipped with a 25‐kN load cell. For the fixation in the testing machine, each vertebra was embedded in polymethylmethacrylate (PMMA) resin (Technovit Universal Fluid and Powder 2060, Heraeus Kulzer GmbH, Wehrheim, Germany).…”

“…One possibility to increase the mechanical strength of the screw–bone interface is cement augmentation of the pedicle screw. Numerous biomechanical studies have demonstrated increased pull‐out strength of pedicle screws after augmentation with bone cement. Furthermore, clinical long‐term studies have also proven the good functional outcome and low revision rates using cement‐augmented pedicle screws.…”

Reduced cement volume does not affect screw stability in augmented pedicle screws

“…Cement augmentation of pedicle screws is increasingly used in order to improve fixation strength in osteoporotic patients [12][13][14][15]. Biomechanical studies have shown an approximately twofold increase in pull-out force and an increase in load to failure in cyclic testing by 52% for augmented pedicle screws [16][17][18][19]. However, cement augmentation of pedicle screws is associated with relevant complications such as leakage and embolism [20,21].…”

Comparison of unilateral and bilateral polymethylmethacrylate-augmented cannulated pedicle screw fixation for the management of lumbar spondylolisthesis with osteoporosis

“…The primary focus has been on increasing stability by improving the side hole design of the screw (6,7), as well as the optimization of the dose of PMMA in surgery (8,9). The safety and effectiveness of CPSs have been partially con rmed in previous studies (4,5).…”