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. 2023 Nov 10;18(1):855.
doi: 10.1186/s13018-023-04349-5.

Finite element analysis comparing a PEEK posterior fixation device versus pedicle screws for lumbar fusion

Robert K Eastlack  1 , Pierce D Nunley  2 , Kornelis A Poelstra  3 , Alexander R Vaccaro  3 , Marcus Stone  2 , Larry E Miller  4 , Pierre Legay  5 , Julien Clin  5 , Aakash Agarwal  6
Affiliations

Finite element analysis comparing a PEEK posterior fixation device versus pedicle screws for lumbar fusion

Robert K Eastlack et al. J Orthop Surg Res. .

Abstract

Background: Pedicle screw loosening and breakage are common causes of revision surgery after lumbar fusion. Thus, there remains a continued need for supplemental fixation options that offer immediate stability without the associated failure modes. This finite element analysis compared the biomechanical properties of a novel cortico-pedicular posterior fixation (CPPF) device with those of a conventional pedicle screw system (PSS).

Methods: The CPPF device is a polyetheretherketone strap providing circumferential cortical fixation for lumbar fusion procedures via an arcuate tunnel. Using a validated finite element model, we compared the stability and load transfer characteristics of CPPF to intact conditions under a 415 N follower load and PSS conditions under a 222 N preload. Depending on the instrumented levels, two different interbody devices were used: a lateral lumbar interbody device at L4-5 or an anterior lumbar interbody device at L5-S1. Primary outcomes included range of motion of the functional spinal units and anterior load transfer, defined as the total load through the disk and interbody device after functional motion and follower load application.

Results: Across all combinations of interbody devices and lumbar levels evaluated, CPPF consistently demonstrated significant reductions in flexion (ranging from 90 to 98%), extension (ranging from 88 to 94%), lateral bending (ranging from 75 to 80%), and torsion (ranging from 77 to 86%) compared to the intact spine. Stability provided by the CPPF device was comparable to PSS in all simulations (range of motion within 0.5 degrees for flexion-extension, 0.6 degrees for lateral bending, and 0.5 degrees for torsion). The total anterior load transfer was higher with CPPF versus PSS, with differences across all tested conditions ranging from 128 to 258 N during flexion, 89-323 N during extension, 135-377 N during lateral bending, 95-258 N during torsion, and 82-250 N during standing.

Conclusion: Under the modeled conditions, cortico-pedicular fixation for supplementing anterior or lateral interbody devices between L4 and S1 resulted in comparable stability based on range of motion measures and less anterior column stress shielding based on total anterior load transfer measures compared to PSS. Clinical studies are needed to confirm these finite element analysis findings.

Keywords: Cortical fixation; Karma; Lumbar spine; Pedicle screw; Posterior fixation.

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Conflict of interest statement

KP has no relevant financial or non-financial interests to disclose. RE, PN, LM, PL, JC, and AA disclose consultancy with Spinal Elements (Carlsbad, CA, USA). AV discloses consultancy with Globus. He has also served on the scientific advisory board/board of directors/committees for Accelus, Sentryx, AOSpine, and National Spine Health Foundation. He has received royalty payments from Atlas Spine, Medtronic, Stryker Spine, Globus, Aesculap, Thieme, Jaypee, Elsevier, and Taylor Francis/Hodder and Stoughton. He has stock/stock option ownership interests in Accelus, Atlas Spine, AVKN Patient Driving Care, Replication Medica, Globus, Paradigm Spine, Stout Medical, Progressive Spinal Technologies, Advanced Spinal Intellectual Properties, Spine Medica, Computational Biodynamics, Spineology, Orthobullets, Parvizi Surgical Innoavtion, In Vivo, Flagship Surgical, Cytonics, Bonovo Orthopaedics, Electrocore, FlowPharma, R.S.I., Rothman Institute and Related Properties, Innovative Surgical Design, and Avaz Surgical. In addition, he has also provided expert testimony. He has also served as deputy editor/editor of Clinical Spine Surgery. MS reports consulting with Camber Spine, K2M. NuVasive, Organogenesis, ReGelTec, Simplify Medical, Spineology, and Zimmer Biomet; and a grant from Wright Medical.

Figures

Fig. 1
Fig. 1
L4–S1 spine, color scale (in mm) shows the deformation on lateral bending for the intact spine (left), cortico-pedicular posterior fixation (CPPF) device (middle), and pedicle screw system (PSS) (right)
Fig. 2
Fig. 2
L4–L5 cortico-pedicular posterior fixation (CPPF) device and pedicle screw system (PSS)-instrumented spine model, with an example of bone and instrumentation meshing detail
Fig. 3
Fig. 3
Comparison of the moment-rotation curves between Panjabi data [27] and the finite element model (FEM) for the extension-flexion stiffness of the spinal functional unit L4–L5
Fig. 4
Fig. 4
Moment-rotation curve in flexion–extension with the cortico-pedicular posterior fixation (CPPF) device, pedicle screw system (PSS), and intact spine at one or two operated segments. At a pure moment of 7.5 Nm, flexion–extension between the CPPF device and PSS was within 0.5 degrees under all loading conditions
Fig. 5
Fig. 5
Moment-rotation curve in lateral bending with the cortico-pedicular posterior fixation (CPPF) device, pedicle screw system (PSS), and intact spine at one or two operated segments. At a pure moment of 7.5 Nm, lateral bending between the CPPF device and PSS was within 0.6 degrees under all loading conditions
Fig. 6
Fig. 6
Moment-rotation curve in torsion with a cortico-pedicular posterior fixation (CPPF) device, pedicle screw system (PSS), and intact spine at one or two operated segments. At a pure moment of 7.5 Nm, torsion between the CPPF device and PSS was within 0.5 degrees under all loading conditions
Fig. 7
Fig. 7
Total anterior load transfer with a cortico-pedicular posterior fixation (CPPF) device, pedicle screw system (PSS), and intact spine. Anterior loading between PSS and CPPF is reported across four instrumented spinal levels from three separate finite element analysis models including single-level lateral lumbar interbody fusion (LLIF) with PSS or CPPF (1 level), two-level LLIF with PSS or CPPF (2 levels), and single-level anterior lumbar interbody fusion (ALIF) with PSS or CPPF (1 level)
Fig. 8
Fig. 8
Cortico-pedicular posterior fixation (CPPF) device tensile force at maximal loading under flexion, extension, standing, torsion, and right lateral bending
See this image and copyright information in PMC

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