Minimizing Pedicle Screw Pullout Risks: A Detailed Biomechanical Analysis of Screw Design and Placement

Rohan-Jean Bianco (1) , Pierre-Jean Arnoux (2) , Eric Wagnac (2) , Jean-Marc Mac-Thiong (3) , Carl-Eric Aubin (1, 4)

1 Department of Mechanical Engineering
2 LBA UMR T24 - Laboratoire de Biomécanique Appliquée
3 Department of Surgery
4 CHU Sainte Justine [Montréal]

STUDY DESIGN: Detailed biomechanical analysis of the anchorage performance provided by different pedicle screw design and placement strategies under pullout loading. OBJECTIVE: To biomechanically characterize the specific effects of surgeon-specific pedicle screw design parameters on anchorage performance using a finite element model (FEM). SUMMARY OF BACKGROUND DATA: Pedicle screw fixation is commonly used in the treatment of spinal pathologies. However, there is little consensus on the selection of an optimal screw type, size, and insertion trajectory depending on vertebra dimension and shape. METHODS: Different screw diameters and lengths, threads and insertion trajectories were computationally tested using a design of experiment (DOE) approach. A detailed FEM of an L3 vertebra was created including elastoplastic bone properties and contact interactions with the screws. Loads and boundary conditions were applied to the screws to simulate axial pullout tests. Force-displacement responses and internal stresses were analyzed to determine the specific effects of each parameter. RESULTS: The DOE analysis revealed significant effects (p<0.01) for all tested principal parameters along with the interactions between diameter and trajectory. Screw diameter had the greatest impact on anchorage performance. The best insertion trajectory to resist pullout involved placing the screw threads closer to the pedicle walls using the straight-forward insertion technique, which showed the importance of the cortical layer grip. The simulated cylindrical single-lead thread screws presented better biomechanical anchorage than the conical dual-lead thread screws in axial loading conditions. CONCLUSIONS: The model made it possible to quantitatively measure the effects of both screw design characteristics and surgical choices, enabling to recommend strategies to improvesingle pedicle screw performance under axial loading

Mots clés: FINITE ELEMENT ANALYSIS; PEDICLE SCREW; PULLOUT TEST; SPINAL INSTRUMENTATION

Mots clés: METHODE DES ELEMENTS FINIS; COLONNE VERTEBRALE; BIOMECANIQUE; MODELISATION NUMERIQUE

Domaines: Ingénierie biomédicale; Biomécanique [physics.med-ph]; Chirurgie

Rohan-Jean Bianco, Pierre-Jean Arnoux, Eric Wagnac, Jean-Marc Mac-Thiong, Carl-Eric Aubin. Minimizing Pedicle Screw Pullout Risks: A Detailed Biomechanical Analysis of Screw Design and Placement. Clinical Spine Surgery, 2016, 31p. ⟨10.1097/BSD.0000000000000151⟩. ⟨hal-01472882v2⟩