https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Sun, 08 Mar 2026 11:07:25 GMT 2026-03-08T11:07:25Z http://hdl.handle.net/10985/18099 Limiting interpedicular screw displacement increases shear forces in screws: A finite element study LIMA, Lucas Venancio; CHARLES, Yann-Philippe; SKALLI, Wafa; ROUCH, Philippe Background context: Screw loosening has been reported for non-fusion devices. Forces on pedicle screwscould be related to kinematic parameters as the interpedicular displacement (ID), which consists of thedisplacement between superior and inferior screw heads from full extension to full flexion.Purpose: To investigate the relationship between ID and screw loosening for different designs of posteriorimplants using a finite element model.Methods: An L3-sacrum previously validated spine FE model was used. Three-rod designs were consid-ered in L4-L5 segment: a rigid screw-rod implant, a flexible one and a specific design with a sliding rodproviding limited restrain in ID. In order to simulate intermediate configurations, the friction coefficientbetween the sliding rods and connectors were varied. The sacrum was rigidly fixed. Rotations (flexion-extension, lateral bending and axial rotation) were applied to L3, for each modeled configuration: intact,injured, injured with different implants. Model consistency was checked with existing experimentalin vitro data on intact and instrumented segments. Screw loads were computed as well as ID.Results: In flexion-extension, the ID was less than 2 mm for rigid (R) and flexible (F) constructs and 5.5 mmfor intact spine and the sliding implant (S3). Screw’s shear forces were 272 N, 153 N, 43 N respectivelyfor R, F and S3 constructs.Conclusions: Implants that allow ID presented lower screws loads. A compromise between the abilityof the implant to withstand compressive forces, which requires longitudinal stiffness, and its ability toallow ID could be important for future implant designs in order to prevent screw loosening. Sun, 01 Jan 2017 00:00:00 GMT http://hdl.handle.net/10985/18099 2017-01-01T00:00:00Z LIMA, Lucas Venancio CHARLES, Yann-Philippe SKALLI, Wafa ROUCH, Philippe Background context: Screw loosening has been reported for non-fusion devices. Forces on pedicle screwscould be related to kinematic parameters as the interpedicular displacement (ID), which consists of thedisplacement between superior and inferior screw heads from full extension to full flexion.Purpose: To investigate the relationship between ID and screw loosening for different designs of posteriorimplants using a finite element model.Methods: An L3-sacrum previously validated spine FE model was used. Three-rod designs were consid-ered in L4-L5 segment: a rigid screw-rod implant, a flexible one and a specific design with a sliding rodproviding limited restrain in ID. In order to simulate intermediate configurations, the friction coefficientbetween the sliding rods and connectors were varied. The sacrum was rigidly fixed. Rotations (flexion-extension, lateral bending and axial rotation) were applied to L3, for each modeled configuration: intact,injured, injured with different implants. Model consistency was checked with existing experimentalin vitro data on intact and instrumented segments. Screw loads were computed as well as ID.Results: In flexion-extension, the ID was less than 2 mm for rigid (R) and flexible (F) constructs and 5.5 mmfor intact spine and the sliding implant (S3). Screw’s shear forces were 272 N, 153 N, 43 N respectivelyfor R, F and S3 constructs.Conclusions: Implants that allow ID presented lower screws loads. A compromise between the abilityof the implant to withstand compressive forces, which requires longitudinal stiffness, and its ability toallow ID could be important for future implant designs in order to prevent screw loosening. http://hdl.handle.net/10985/18395 Clinical Outcomes and Complications After Pedicle-anchored Dynamic or Hybrid Lumbar Spine Stabilization : A Systematic Literature Review PRUD'HOMME, Marion; BARRIOS, Carlos; CHARLES, Yann-Philippe; STEIB, Jean-Paul; SKALLI, Wafa; ROUCH, Philippe Fusion is the standard in-strumentation for many pathologies of the lumbar spine. Wor-rying rates of failure, including adjacent segment degeneration (ASD), have consistently been reported. The interest for dy-namic stabilization came from the need of minimizing the long-term complications related to the restriction of the lumbar motion. However, pedicle-based dynamic stabilization advan-tages and drawbacks remain controversial. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/18395 2015-01-01T00:00:00Z PRUD'HOMME, Marion BARRIOS, Carlos CHARLES, Yann-Philippe STEIB, Jean-Paul SKALLI, Wafa ROUCH, Philippe Fusion is the standard in-strumentation for many pathologies of the lumbar spine. Wor-rying rates of failure, including adjacent segment degeneration (ASD), have consistently been reported. The interest for dy-namic stabilization came from the need of minimizing the long-term complications related to the restriction of the lumbar motion. However, pedicle-based dynamic stabilization advan-tages and drawbacks remain controversial. http://hdl.handle.net/10985/20231 The effect of posterior non-fusion instrumentation on segmental shear loading of the lumbar spine CHARLES, Yann-Philippe; PERSOHN, Sylvain; STEIB, Jean-Paul; SAULEAU, E.A.; SKALLI, Wafa; ROUCH, Philippe Background : Lumbar stenosis and facet osteoarthritis represent indications for decompression and instrumentation. It is unclear if degenerative spondylolisthesis grade I with a remaining disc height could be an indication for non-fusion instrumentation. The purpose of this study was to determine the influence of a mobile pedicle screw based device on lumbar segmental shear loading, thus simulating the condition of spondylolisthesis. Materials and methods : Six human cadaver specimens were tested in 3 configurations: intact L4–L5 segment, then facetectomy plus undercutting laminectomy, then instrumentation with lesion. A static axial compression of 400 N was applied to the lumbar segment and anterior displacements of L4 on L5 were measured for posterior-anterior shear forces from 0 to 200 N. The slope of the loading curve was assessed to determine shear stiffness. Results : Homogenous load-displacement curves were obtained for all specimens. The average intact anterior displacement was 1.2 mm. After lesion, the displacement increased by 0.6 mm compared to intact (P = 0.032). The instrumentation decreased the displacement by 0.5 mm compared to lesion (P = 0.046). The stiffness's were: 162 N/mm for intact, 106 N/mm for lesion, 148 N/mm for instrumentation. The difference was not significant between instrumented and intact segments (P = 0.591). Conclusions : Facetectomy plus undercutting laminectomy decreases segmental shear stiffness and increases anterior translational L4–L5 displacement. Shear stiffness of the instrumented segment is higher with the device and anterior displacements under shear loading are similar to the intact spine. This condition could theoretically be interesting for the simulation of non-fusion instrumentation in degenerative spondylolisthesis. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/20231 2014-01-01T00:00:00Z CHARLES, Yann-Philippe PERSOHN, Sylvain STEIB, Jean-Paul SAULEAU, E.A. SKALLI, Wafa ROUCH, Philippe Background : Lumbar stenosis and facet osteoarthritis represent indications for decompression and instrumentation. It is unclear if degenerative spondylolisthesis grade I with a remaining disc height could be an indication for non-fusion instrumentation. The purpose of this study was to determine the influence of a mobile pedicle screw based device on lumbar segmental shear loading, thus simulating the condition of spondylolisthesis. Materials and methods : Six human cadaver specimens were tested in 3 configurations: intact L4–L5 segment, then facetectomy plus undercutting laminectomy, then instrumentation with lesion. A static axial compression of 400 N was applied to the lumbar segment and anterior displacements of L4 on L5 were measured for posterior-anterior shear forces from 0 to 200 N. The slope of the loading curve was assessed to determine shear stiffness. Results : Homogenous load-displacement curves were obtained for all specimens. The average intact anterior displacement was 1.2 mm. After lesion, the displacement increased by 0.6 mm compared to intact (P = 0.032). The instrumentation decreased the displacement by 0.5 mm compared to lesion (P = 0.046). The stiffness's were: 162 N/mm for intact, 106 N/mm for lesion, 148 N/mm for instrumentation. The difference was not significant between instrumented and intact segments (P = 0.591). Conclusions : Facetectomy plus undercutting laminectomy decreases segmental shear stiffness and increases anterior translational L4–L5 displacement. Shear stiffness of the instrumented segment is higher with the device and anterior displacements under shear loading are similar to the intact spine. This condition could theoretically be interesting for the simulation of non-fusion instrumentation in degenerative spondylolisthesis.