Maeva Lopez Poncelas1,2, Luigi La Barbera1,2,3, Jeremy Rawlinson1,4, Dennis Crandall5,6,7, Carl-Eric Aubin8,9. 1. Department of Mechanical Engineering, Polytechnique Montréal, Downtown Station, P.O. Box 6079, Montreal, QC, H3C 3A7, Canada. 2. Research Center, Sainte-Justine University Hospital Center, 3175, Cote Sainte-Catherine Road, Montreal, QC, H3T 1C5, Canada. 3. Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Laboratory of Biological Structure Mechanics, Politecnico di Milano, 32, Piazza Leonardo da Vinci, 32 20133, Milan, MI, Italy. 4. Spine Applied Research, Cranial and Spinal Technologies Medtronic, 18400 Pyramid Place, Memphis, TN, 38132, USA. 5. Sonoran Spine Center, 1255 W Rio Salado Pkwy #107, Tempe, AZ, 85281, USA. 6. Mayo Clinic, 5779 E Mayo Blvd, Phoenix, AZ, 85054, USA. 7. University of Arizona School of Medicine, 475 N 5th St, Phoenix, AZ, 85004, USA. 8. Department of Mechanical Engineering, Polytechnique Montréal, Downtown Station, P.O. Box 6079, Montreal, QC, H3C 3A7, Canada. Carl-Eric.Aubin@polymtl.ca. 9. Research Center, Sainte-Justine University Hospital Center, 3175, Cote Sainte-Catherine Road, Montreal, QC, H3T 1C5, Canada. Carl-Eric.Aubin@polymtl.ca.
Abstract
STUDY DESIGN: Assessment of different proximal instrumentation stiffness features to minimize the mechanical proximal junctional failure-related risks through computer-based biomechanical models. OBJECTIVE: To biomechanically assess variations of proximal instrumentation and loads acting on the spine and construct to minimize proximal junctional failure (PJF) risks. The use of less-stiff fixation such as hooks or tensioned bands, compared to pedicle screws, at the proximal instrumentation level are considered to allow for a gradual transition in stiffness with the adjacent levels, but the impact of such flexible fixation on the loads balance and complications such as PJF remain uncertain. METHODS: Six patients with adult spine deformity who underwent posterior spinal instrumentation were used to numerically model and simulate the surgical steps, erected posture, and flexion functional loading in patient-specific multibody analyses. Three types of upper-level fixation (pedicle screws (PS), supralaminar hooks (SH), and sublaminar bands (SB) with tensions of 50, 250, and 350 N) and rod stiffness (CoCr/6 mm, CoCr/5.5 mm, Ti/5.5 mm) were simulated. The loads acting on the spine and implants of the 90 simulated configurations were analyzed using Kruskal-Wallis statistical tests. RESULTS: Simulated high-tensioned bands decreased the sagittal moment at the adjacent level proximal to the instrumentation (1.3 Nm at 250 N; 2.5 Nm at 350 N) compared to screws alone (PS) (15.6 Nm). At one level above, the high-tensioned SB increased the sagittal moment (17.7 Nm-SB vs. 15.5 Nm-PS) and bending moment on the rods (5.4 Nm and 5.7 Nm vs. 0.6 Nm) (p < 0.05). SB with 50 N tension yielded smaller changes in load transition compared to higher tension, with moments of 8.1 Nm and 16.8 Nm one and two levels above the instrumentation. The sagittal moment at the upper implant-vertebra connection decreased with the rod stiffness (1.0 Nm for CoCr/6 mm vs. 0.7 Nm for Ti/5.5 mm; p < 0.05). CONCLUSION: Simulated sublaminar bands with lower tension produced smaller changes in the load transition across proximal junctional levels. Decreasing the rod stiffness further modified these changes, with a decrease in loads associated with bone failure, however, lower stiffness did increase the rod breakage risk. LEVEL OF EVIDENCE: N/A.
STUDY DESIGN: Assessment of different proximal instrumentation stiffness features to minimize the mechanical proximal junctional failure-related risks through computer-based biomechanical models. OBJECTIVE: To biomechanically assess variations of proximal instrumentation and loads acting on the spine and construct to minimize proximal junctional failure (PJF) risks. The use of less-stiff fixation such as hooks or tensioned bands, compared to pedicle screws, at the proximal instrumentation level are considered to allow for a gradual transition in stiffness with the adjacent levels, but the impact of such flexible fixation on the loads balance and complications such as PJF remain uncertain. METHODS: Six patients with adult spine deformity who underwent posterior spinal instrumentation were used to numerically model and simulate the surgical steps, erected posture, and flexion functional loading in patient-specific multibody analyses. Three types of upper-level fixation (pedicle screws (PS), supralaminar hooks (SH), and sublaminar bands (SB) with tensions of 50, 250, and 350 N) and rod stiffness (CoCr/6 mm, CoCr/5.5 mm, Ti/5.5 mm) were simulated. The loads acting on the spine and implants of the 90 simulated configurations were analyzed using Kruskal-Wallis statistical tests. RESULTS: Simulated high-tensioned bands decreased the sagittal moment at the adjacent level proximal to the instrumentation (1.3 Nm at 250 N; 2.5 Nm at 350 N) compared to screws alone (PS) (15.6 Nm). At one level above, the high-tensioned SB increased the sagittal moment (17.7 Nm-SB vs. 15.5 Nm-PS) and bending moment on the rods (5.4 Nm and 5.7 Nm vs. 0.6 Nm) (p < 0.05). SB with 50 N tension yielded smaller changes in load transition compared to higher tension, with moments of 8.1 Nm and 16.8 Nm one and two levels above the instrumentation. The sagittal moment at the upper implant-vertebra connection decreased with the rod stiffness (1.0 Nm for CoCr/6 mm vs. 0.7 Nm for Ti/5.5 mm; p < 0.05). CONCLUSION: Simulated sublaminar bands with lower tension produced smaller changes in the load transition across proximal junctional levels. Decreasing the rod stiffness further modified these changes, with a decrease in loads associated with bone failure, however, lower stiffness did increase the rod breakage risk. LEVEL OF EVIDENCE: N/A.
Authors: Shay Bess; Jeffrey E Harris; Alexander W L Turner; Virginie LaFage; Justin S Smith; Christopher I Shaffrey; Frank J Schwab; Regis W Haid Journal: J Neurosurg Spine Date: 2016-09-09
Authors: Remco J P Doodkorte; Alex K Roth; Jacobus J Arts; L M Arno Lataster; Lodewijk W van Rhijn; Paul C Willems Journal: Spine J Date: 2021-01-23 Impact factor: 4.166
Authors: Tobias Lange; Werner Schmoelz; Georg Gosheger; Martin Eichinger; Christian H Heinrichs; Albert Schulze Boevingloh; Tobias L Schulte Journal: Spine J Date: 2017-03-31 Impact factor: 4.166