Biomechanical analysis in a human cadaveric model of spinous process fixation with an interlaminar allograft spacer for lumbar spinal stenosis

Laboratory investigation

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Traditional posterior pedicle screw fixation is well established as the standard for spinal stabilization following posterior or posterolateral lumbar fusion. In patients with lumbar spinal stenosis requiring segmental posterior instrumented fusion and decompression, interlaminar lumbar instrumented fusion (ILIF) is a potentially less invasive alternative with reduced morbidity and includes direct decompression assisted by an interlaminar allograft spacer stabilized by a spinous process plate. To date, there has been no biomechanical study on this technique. In the present study the biomechanical properties of the ILIF construct were evaluated using an in vitro cadaveric biomechanical analysis, and the results are presented in comparison with other posterior fixation techniques.


Eight L1–5 cadaveric specimens were subjected to nondestructive multidirectional testing. After testing the intact spine, the following conditions were evaluated at L3–4: bilateral pedicle screws, bilateral laminotomy, ILIF, partial laminectomy, partial laminectomy plus unilateral pedicle screws, and partial laminectomy plus bilateral screws. Intervertebral motions were measured at the index and adjacent levels.


Bilateral pedicle screws without any destabilization provided the most rigid construct. In flexion and extension, ILIF resulted in significantly less motion than the intact spine (p < 0.05) and no significant difference from the laminectomy with bilateral pedicle screws (p = 0.76). In lateral bending, there was no statistical difference between ILIF and laminectomy with unilateral pedicle screws (p = 0.11); however, the bilateral screw constructs were more rigid (p < 0.05). Under axial rotation, ILIF was not statistically different from laminectomy with unilateral or bilateral pedicle screws or from the intact spine (p > 0.05). Intervertebral motions adjacent to ILIF were typically lower than those adjacent to laminectomy with bilateral pedicle screws.


Stability of the ILIF construct was not statistically different from bilateral pedicle screw fixation following laminectomy in the flexion and extension and axial rotation directions, while adjacent segment motions were decreased. The ILIF construct may allow surgeons to perform a minimally invasive, single-approach posterior decompression and instrumented fusion without the added morbidity of traditional pedicle screw fixation and posterolateral fusion.

Abbreviations used in this paper:bL = bilateral laminotomy; bPS = bilateral pedicle screw; ILIF = interlaminar lumbar instrumented fusion; pL = partial laminectomy; ROM = range of motion; uPS = unilateral pedicle screw.

Article Information

Address correspondence to: Hyun W. Bae, M.D., Spine Research Foundation, Spine Institute at Saint John's Health Center, Santa Monica, California 90404. email:

Please include this information when citing this paper: published online April 20, 2012; DOI: 10.3171/2012.3.SPINE11631.

© AANS, except where prohibited by US copyright law.



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    Photograph depicting ILIF construct on a cadaveric lumbar specimen at L3–4.

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    Lateral fluoroscopy images of the ILIF (upper) and pL + bPS (lower) test conditions in the unloaded position while mounted on the spine testing system.

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    Bar graphs demonstrating the mean angular ROM at L3–4 in flexion and extension (A), lateral bending (B), and axial rotation (C) for all conditions studied. Error bars show ± 1 SEM.

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    Bar graphs showing the mean percent change in adjacent-level ROM with respect to the intact spine in response to loading in each direction: flexion and extension (A), lateral bending (B), and axial rotation (C). Error bars show ± 1 SEM.



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