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. 2019 Oct 25;20(1):470.
doi: 10.1186/s12891-019-2886-4.

Effect of lordosis on adjacent levels after lumbar interbody fusion, before and after removal of the spinal fixator: a finite element analysis

Fon-Yih Tsuang  1   2 , Jui-Chang Tsai  3 , Dar-Ming Lai  4
Affiliations

Effect of lordosis on adjacent levels after lumbar interbody fusion, before and after removal of the spinal fixator: a finite element analysis

Fon-Yih Tsuang et al. BMC Musculoskelet Disord. .

Abstract

Background: Literature indicates that adjacent-segment diseases after posterior lumbar interbody fusion with pedicle screw fixation accelerate degenerative changes at unfused adjacent segments due to the increased motion and intervertebral stress. Sagittal alignment of the spine is an important consideration as achieving proper lordosis could improve the outcome of spinal fusion and avoid the risk of adjacent segment diseases. Therefore, restoration of adequate lumbar lordosis is considered as a major factor in the long-term success of lumbar fusion. This study hypothesized that the removal of internal fixation devices in segments that have already fused together could reduce stress at the disc at adjacent segments, particularly in patients with inadequate lordosis. The purpose of this study was to analyze the biomechanical characteristics of a single fusion model (posterior lumbar interbody fusion with internal fixation) with different lordosis angles before and after removal of the internal fixation device.

Methods: Five finite element models were constructed for analysis; 1) Intact lumbar spine without any implants (INT), 2) Lumbar spine implanted with a spinal fixator and lordotic intervertebral cage at L4-L5 (FUS-f-5c), 3) Lumbar spine after removal of the spinal fixator (FUS-5c), 4) Lumbar spine implanted with a spinal fixator and non-lordotic intervertebral cage at L4-L5 (FUS-f-0c), and 5) Lumbar spine after removal of the spinal fixator from the FUS-f-0c model (FUS-0c).

Results: The ROM of adjacent segments in the FUS-f-0c model was found to be greater than in the FUS-f-5c model. After removing the fixator, the adjacent segments in the FUS-5c and FUS-0c models had a ROM that was similar to the intact spine under all loading conditions. Removing the fixator also reduced the contact forces on adjacent facet joints and reduced the peak stresses on the discs at adjacent levels. The greatest increase in stress on the discs was found in the FUS-f-0c model (at both L2/L3 and L3/L4), with intervertebral stress at L3/L4 increasing by 83% when placed in flexion.

Conclusions: This study demonstrated how removing the spinal fixation construct after bone fusion could reduce intradiscal pressure and facet contact forces at adjacent segments, while retaining a suitable level of lumbar lordosis.

Keywords: Finite element analysis; Spinal fixator; adjacent-segment disease; lumbar lordosis; posterior lumbar fusion.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
FE models of the spine with a spinal fixator and with the fixator removed; a) Bones, intervertebral discs, and ligaments of the intact spine. b) Mesh of intact FE models used in this study. c) The fusion and fixation model, with the L4–L5 segment immobilized by a posterior spinal fixator and fused by a stand-alone cage placed with the posterior corner
Fig. 2
Fig. 2
The a) range of motion (ROM), b) facet joint forces and c) disc stresses of all models normalized by the INT model
See this image and copyright information in PMC

References

    1. Periasamy K, Shah K, Wheelwright EF. Posterior lumbar interbody fusion using cages, combined with instrumented posterolateral fusion: a study of 75 cases. Acta Orthop Belg [Internet]. 2008 Apr [cited 2019 Sep 9];74(2):240–8. Available from: http://www.ncbi.nlm.nih.gov/pubmed/18564483. - PubMed
    1. Brantigan JW, Steffee AD, Lewis ML, Quinn LM, Persenaire JM. Lumbar interbody fusion using the Brantigan I/F cage for posterior lumbar interbody fusion and the variable pedicle screw placement system: two-year results from a Food and Drug Administration investigational device exemption clinical trial. Spine (Phila Pa 1976) [Internet]. 2000 Jun 1 [cited 2018 Nov 22];25(11):1437–46. Available from: http://www.ncbi.nlm.nih.gov/pubmed/10828927. - PubMed
    1. Aiki Hikono, Ohwada Osamu, Kobayashi Hiroji, Hayakawa Mitsuru, Kawaguchi Satoshi, Takebayashi Tsuneo, Yamashita Toshihiko. Adjacent segment stenosis after lumbar fusion requiring second operation. Journal of Orthopaedic Science. 2005;10(5):490–495. doi: 10.1007/s00776-005-0919-3. - DOI - PubMed
    1. Lee JC, Kim Y, Soh JW, Shin BJ. Risk factors of adjacent segment disease requiring surgery after lumbar spinal fusion: Comparison of posterior lumbar interbody fusion and posterolateral fusion. Spine (Phila Pa 1976) 2014;39:5. - PubMed
    1. Nakashima H, Kawakami N, Tsuji T, Ohara T, Suzuki Y, Saito T, et al. Adjacent Segment Disease After Posterior Lumbar Interbody Fusion: Based on Cases With a Minimum of 10 Years of Follow-up. Spine (Phila Pa 1976) [Internet]. 2015 Jul 15 [cited 2019 Sep 9];40(14):E831–41. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25839385. - PubMed

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