Pullout strength of pedicle screws with cement augmentation in severe osteoporosis: A comparative study between cannulated screws with cement injection and solid screws with cement pre-filling

Abstract

BackgroundPedicle screws with PMMA cement augmentation have been shown to significantly improve the fixation strength in a severely osteoporotic spine. However, the efficacy of screw fixation for different cement augmentation techniques, namely solid screws with retrograde cement pre-filling versus cannulated screws with cement injection through perforation, remains unknown. This study aimed to determine the difference in pullout strength between conical and cylindrical screws based on the aforementioned cement augmentation techniques. The potential loss of fixation upon partial screw removal after screw insertion was also examined.MethodThe Taguchi method with an L8 array was employed to determine the significance of design factors. Conical and cylindrical pedicle screws with solid or cannulated designs were installed using two different screw augmentation techniques: solid screws with retrograde cement pre-filling and cannulated screws with cement injection through perforation. Uniform synthetic bones (test block) simulating severe osteoporosis were used to provide a platform for each screw design and cement augmentation technique. Pedicle screws at full insertion and after a 360-degree back-out from full insertion were then tested for axial pullout failure using a mechanical testing machine.ResultsThe results revealed the following 1) Regardless of the screw outer geometry (conical or cylindrical), solid screws with retrograde cement pre-filling exhibited significantly higher pullout strength than did cannulated screws with cement injection through perforation (p = 0.0129 for conical screws; p = 0.005 for cylindrical screws). 2) For a given cement augmentation technique (screws without cement augmentation, cannulated screws with cement injection or solid screws with cement pre-filling), no significant difference in pullout strength was found between conical and cylindrical screws (p >0.05). 3) Cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Observations of the failed specimens indicated that failure occurred at the composite/bone interface, whereas the composite remained well bonded to the screws. This result implies that the screw/composite interfacial strength was much higher than the composite/bone interfacial strength. 4) The back-out of the screw by 360 degrees from full insertion did not decrease the pullout strength in any of the studied cases. 5) Generally, larger standard deviations were found for the screw back-out cases, implying that the results of full insertion cases are more repeatable than those of the back-out cases.ConclusionsSolid screws with retrograde cement pre-filling offer improved initial fixation strength when compared to that of cannulated screws with cement injection through perforation for both the conically and cylindrically shaped screw. Our results also suggest that the fixation screws can be backed out by 360 degrees for intra-operative adjustment without the loss of fixation strength.

Quantitative dual-energy CT for phantomless evaluation of cancellous bone mineral density of the vertebral pedicle: correlation with pedicle screw pull-out strength

“…Stability of transpedicular screw fixation in healthy and osteoporotic bone has been assessed in cadaver studies with pedicle screw pullout strength [3]. Prior biomechanical studies have also proposed several techniques to increase screw pull-out strength based on alteration of insertion angle [4], modification of M. Fawad Khan and Konstantinos Kafchitsas contributed equally to this work and share senior authorship screw design [5] and timing of perioperative cement injection [6,7].…”

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

“…The Sawbones mimicked human vertebrae with severe osteoporosis and provided a homogeneous and consistent material similar to human cancellous bone, as well as X-ray inspection capacity. 20 …”

Augmented PMMA distribution: improvement of mechanical property and reduction of leakage rate of a fenestrated pedicle screw with diameter-tapered perforations

“…1,7,14,17,21,24 The main difference among these FPSs is the number of side perforations. Regardless of the different number of perforations, the pullout strength of PMMA-augmented FPSs is greater than that of nonaugmented conventional screws 3,5,9,10,12,26 or cannulated screws 8,16,18 in the osteoporotic condition. In the present study, compared with the nonaugmented CPS group, FPS-A1.0, 1.5, and 2.0 achieved 137%, 207%, and 265% increased pullout strengths, respectively, and FPS-B1.0, 1.5, and 2.0 achieved 166%, 232%, and 269% increased pullout strengths, respectively.…”

“…Recently, FPSs with different designs have been studied in vitro [3][4][5][8][9][10]12,16,18,26 and in vivo. 1,7,14,17,21,24 The main difference among these FPSs is the number of side perforations.…”