Biomechanical strength impact of lateral wall breach on spinal pedicle screw fixation

D.-W. Ge, H.-T. Chen, Z.-Y. Qian, S. Zhang, Y. Zhuang, L. Yang, X.-J. Cao, T. Sui

Department of Orthopaedics, the First Affiliated Hospital of Nanjing Medical University, Nanjing, China. xiaojiancao001@126.com

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• Orthopedics

OBJECTIVE: The purpose of our study was to make a comparison between the fixation strength of optimum placed pedicle screw (OS) and re-directionally accurate placed pedicle screw (RS) after lateral pedicle breach.

PATIENTS AND METHODS: A total of 30 fresh lumbar vertebrae (L1-5) were gained from 6 male or female pigs weighing about 100 kg, which were divided into 2 groups according to different ways of pedicle screws placement: OS group (n=30) and RS group (n=30). MTS machine was employed to detect the screw loosening and axial pullout. We examined seating torque, screw-loosening force, the maximal torque and post-loosening axial pullout in each pedicle screw.

RESULTS: Maximal insertion torque of OS was (111.6±8.4) N•cm and RS was (79.0±6.3) N•cm, which indicated a significant difference (Z=3.012, p=0.003). Seating torque of OS and RS were (85.9±5.6) N•cm and (60.3±4.8) N•cm separately, and the difference was statistically significant (Z=2.799, p=0.006). Screw loosening force of OS and RS were (75.9±7.0) N and (52.4±6.3) N respectively, and the difference was statistically significant (Z=2.652, p=0.003). Post-loosening axial pullout force of OS and RS were (328.5±11.3) N and (269.1±9.6) N separately, demonstrating that the difference was statistically significant (Z=2.865, p=0.004).

CONCLUSIONS: RS placement is an alternative for remediation following a lateral wall breach evidenced by significantly decreased seating torque, screw loosening force, the maximal torque and post-loosening axial pullout compared with OS.

Published on: 2018/07/11

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