Comparison of the mechanical properties of two designs of polyaxial pedicle screw

Alicja Kubiak, Katherine Lindqvist-Jones, Karl Dearn, Duncan Shepherd

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
281 Downloads (Pure)


In this study, the mechanical properties of a novel dual-core pedicle screw were compared with a commercially available cylindrical screw. In order to evaluate and compare their mechanical performance, a series of axial pullout, quasi-static and dynamic bend tests were conducted. In the pullout tests, three polyurethane (PU) foams (density: 0.16, 0.32 and 0.64 g/cm3) were used to compare the pullout strength between both screw types. The ultimate static strength of each screw was determined by a series of quasi-static cantilever bend tests. Dynamic tests were performed with a peak forces corresponding to 10%, 30%, 40%, 50%, 65% and 75% of the ultimate static strength of each screw type. Each specimen was subjected to a sinusoidally varying load which continued until the specimen fractured or reached 2.5 million cycles. The results of the pullout force indicated that the dual-core screws had higher pullout strength, in each PU foam, compared to cylindrical screws, however, the differences were not statistically significant. The average stiffness of dual-core screw during pullout from the 0.16 and 0.32 g/cm3 PU foams was significantly higher (p < .05). In quasi-static tests, results of ultimate bending load; bending stiffness and structural stiffness were significantly higher for dual-core screws (p < .05). During the dynamic bending tests, the dual-core screws had longer fatigue lives for all loading levels. It was observed that the fatigue failures for both screw types occurred either at the head-shank junction or between third and fourth thread. In conclusion, the findings of this study indicated that the dual-core screw design has improved mechanical performance compared to the cylindrical design, with the exception of pullout resistance, which showed no significant difference.
Original languageEnglish
JournalEngineering Failure Analysis
Early online date23 Aug 2018
Publication statusE-pub ahead of print - 23 Aug 2018


  • Pedicle screw
  • Pullout
  • Design
  • Quasi-static test
  • Dynamic test


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