Biomechanical evaluation of strategies for adjacent segment disease after lateral lumbar interbody fusion: is the extension of pedicle screws necessary?

Abstract Background: Adjacent segment disease (ASD) is a well-known complication after interbody fusion. Pedicle screw-rod revision possesses sufficient strength and rigidity. However, is a surgical segment with rigid fixation necessary for ASD reoperation? This study aimed to investigate the biomechanical effect of different instrumentation on lateral lumbar interbody fusion (LLIF) for ASD treatment. Methods: A validated L2~5 finite element (FE) model was modified for simulation. ASD was considered the level cranial to the upper-instrumented segment (L3/4). Bone graft fusion in LLIF with bilateral pedicle screw (BPS) fixation occurred at L4/5. The ASD segment for each group underwent a) LLIF + posterior extension of BPS, b) PLIF + posterior extension of BPS, c) LLIF + lateral screw, and d) stand-alone LLIF. The L3/4 range of motion (ROM), interbody cage stress and strain, screw-bone interface stress, cage-endplate interface stress, and L2/3 nucleus pulposus of intradiscal pressure (NP-IDP) analysis were calculated for comparisons among the four models. Results: All reconstructive models displayed decreased motion at L3/4. Under each loading condition, the difference was not significant between models a and b, which provided the maximum ROM reduction (73.8% to 97.7% and 68.3% to 98.4%, respectively). Model c also provided a significant ROM reduction (64.9% to 77.5%). Model d provided a minimal restriction of the ROM (18.3% to 90.1%), which exceeded that of model a by 13.1 times for flexion-extension, 10.3 times for lateral bending and 4.8 times for rotation. Model b generated greater cage stress than other models, particularly for flexion. The maximum displacement of the cage and the peak stress of the cage-endplate interface were found to be the highest in model d under all loading conditions. For the screw-bone interface, the stress was much greater with lateral instrumentation than with posterior instrumentation. Conclusions: Stand-alone LLIF is likely to have limited stability, particularly for lateral bending and axial rotation. Posterior extension of BPS can provide reliable stability and excellent protective effects on instrumentation and endplates. However, LLIF with the use of an in situ screw may be an alternative for ASD reoperation.

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Biomechanical Evaluation of strategies for Adjacent Segment Disease after Lateral lumbar interbody fusion: is extension of pedicle screw necessary?

10.21203/rs.2.17339/v1 ◽

2019 ◽

Author(s):

Ziyang Liang ◽

Jianchao Cui ◽

Jiarui Zhang ◽

Jiahui He ◽

Jingjing Tang ◽

...

Keyword(s):

Pedicle Screw ◽

Interbody Fusion ◽

Adjacent Segment Disease ◽

Adjacent Segment ◽

Fe Model ◽

Rigid Fixation ◽

Lateral Bending ◽

Maximum Displacement ◽

Flexion Extension ◽

Posterior Extension

Abstract Background: Adjacent segment disease (ASD) is a well-known complication after interbody fusion. Pedicle screw-rod revision possessed sufficient strength and rigidity. However, is a surgical segment with rigid fixation necessary for ASD reoperation? This study aimed to investigate the biomechanical effect on LLIF with different instrumentation for ASD treatment.Methods: A validated L2~5 finite element (FE) model was modified to simulate. ASD was considered the level cranial to the upper-instrumented segment(L3/4). Bonegraft fusion in LLIF with bilateral pedicle screw fixation (BPS) has occurred at the L4/5. The ASD segment for each group was underwent a) LLIF + posterior extension of BPS, b) PLIF + posterior extension of BPS, c) LLIF + lateral screw, d) Stand-alone LLIF. L3/4 Range of motion (ROM), interbody cage stress and strain, screw-boneinterface stress, cage-endplate interface stress, and L2/3 nucleus pulposus of intradiscal pressure (NP-IDP) analysis were calculated for the comparisons among fourmodels.Results: All reconstructive models displayed decreased motion at L3/4. In each loading condition, difference was not significant between model a and b, which providedthe maximum ROM reduction (73.8% to 97.7%, 68.3% to 98.4%, respectively). Model c also provided a significant ROM reduction (64.9% to 77.5%). Model d provided a minimal restriction of ROM (18.3% to 90.1%), which exceeded that of model a by 13.1 times in flexion-extension, 10.3 times in lateral bending and 4.8 times in rotation. Model b generated greater cage stress than other models, particularly in flexion. The maximum displacement of the cage and the peak stress of cage-endplate interface were found to be the highest in the model d in all loading conditions. For the screw bone interface, the stress was significantly greater in lateral instrumentation than that of posterior instrumentation.Conclusions: Stand-alone LLIF is likely to have limited stability, particularly in lateral bending and axial rotation. Posterior extension of BPS can provide the reliablystability and excellently protective effect on instrumentation and endplate. However, LLIF with in situ screw may be an alternative for ASD reoperation.

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Adjacent-segment effects of lumbar cortical screw–rod fixation versus pedicle screw–rod fixation with and without interbody support

Journal of Neurosurgery Spine ◽

10.3171/2020.11.spine20977 ◽

2021 ◽

pp. 1-7

Author(s):

Piyanat Wangsawatwong ◽

Anna G. U. Sawa ◽

Bernardo de Andrada Pereira ◽

Jennifer N. Lehrman ◽

Luke K. O’Neill ◽

...

Keyword(s):

Pedicle Screw ◽

Interbody Fusion ◽

Lumbar Fusion ◽

Statistical Significance ◽

Adjacent Segment ◽

Lumbar Interbody Fusion ◽

Lateral Bending ◽

Single Level ◽

Cortical Screw ◽

Flexion Extension

OBJECTIVE Cortical screw–rod (CSR) fixation has emerged as an alternative to the traditional pedicle screw–rod (PSR) fixation for posterior lumbar fixation. Previous studies have concluded that CSR provides the same stability in cadaveric specimens as PSR and is comparable in clinical outcomes. However, recent clinical studies reported a lower incidence of radiographic and symptomatic adjacent-segment degeneration with CSR. No biomechanical study to date has focused on how the adjacent-segment mobility of these two constructs compares. This study aimed to investigate adjacent-segment mobility of CSR and PSR fixation, with and without interbody support (lateral lumbar interbody fusion [LLIF] or transforaminal lumbar interbody fusion [TLIF]). METHODS A retroactive analysis was done using normalized range of motion (ROM) data at levels adjacent to single-level (L3–4) bilateral screw–rod fixation using pedicle or cortical screws, with and without LLIF or TLIF. Intact and instrumented specimens (n = 28, all L2–5) were tested using pure moment loads (7.5 Nm) in flexion, extension, lateral bending, and axial rotation. Adjacent-segment ROM data were normalized to intact ROM data. Statistical comparisons of adjacent-segment normalized ROM between two of the groups (PSR followed by PSR+TLIF [n = 7] and CSR followed by CSR+TLIF [n = 7]) were performed using 2-way ANOVA with replication. Statistical comparisons among four of the groups (PSR+TLIF [n = 7], PSR+LLIF [n = 7], CSR+TLIF [n = 7], and CSR+LLIF [n = 7]) were made using 2-way ANOVA without replication. Statistical significance was set at p < 0.05. RESULTS Proximal adjacent-segment normalized ROM was significantly larger with PSR than CSR during flexion-extension regardless of TLIF (p = 0.02), or with either TLIF or LLIF (p = 0.04). During lateral bending with TLIF, the distal adjacent-segment normalized ROM was significantly larger with PSR than CSR (p < 0.001). Moreover, regardless of the types of screw-rod fixations (CSR or PSR), TLIF had a significantly larger normalized ROM than LLIF in all directions at both proximal and distal adjacent segments (p ≤ 0.04). CONCLUSIONS The use of PSR versus CSR during single-level lumbar fusion can significantly affect mobility at the adjacent segment, regardless of the presence of TLIF or with either TLIF or LLIF. Moreover, the type of interbody support also had a significant effect on adjacent-segment mobility.

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