[Show abstract][Hide abstract] ABSTRACT: BACKGROUND CONTEXT: Stand-alone interbody cages with integrated screws potentially provide a biomechanically stable solution for anterior lumbar interbody fusion (ALIF) that alleviates the need for additional exposure for supplemental fixation, thereby reducing the chance of additional complications and morbidity. PURPOSE: To compare the stability of a stand-alone anterior interbody fusion system with integrated fixation screws against traditional supplemental fixation methods and to evaluate the difference between three and four fixation screws in the stand-alone cage. STUDY DESIGN: In vitro cadaveric biomechanical study. METHODS: Eight cadaveric lumbar spines (L2-sacrum) were tested using a flexibility protocol consisting of three cycles to ±7.5 Nm in flexion-extension, lateral bending, and axial rotation. The conditions evaluated were intact spine; polyether-ether-ketone cage (zero integrated screws) at L4-L5; cage (zero screws)+bilateral pedicle screws (PS); cage (three screws); cage (four screws); cage (zero screws)+anterior plate; and cage (three screws)+spinous process plate. Motion at the index level was assessed using an optoelectronic system. RESULTS: The cage without integrated screws reduced the motion in flexion-extension and lateral bending (p<.001) compared with that in the intact spine. In axial rotation, mean range of motion (ROM) was 8% greater than in intact spine (p>.962). The addition of three integrated screws reduced ROM significantly compared with the cage without screws in all motion planes (p<.001). A fourth screw had no statistically significant effect on the ROM, although there was a trend toward less motion with four screws compared with three. In flexion-extension, the cage with three integrated screws and the spinous process plate was the most rigid condition. There was no significant difference from the bilateral PS (p=.537); however, this was more rigid than all other conditions (p<.024). The most stable condition in lateral bending and axial rotation was the cage with bilateral PS. In lateral bending, the cage (three or four screws) was not significantly different from the cage with anterior plate or the cage (three screws) with spinous process plate fixation; however, only the latter condition was statistically comparable with bilateral PS. In axial rotation, there were no significant differences between the conditions that included integrated screws or supplemental fixation (p>.081). CONCLUSIONS: Biomechanical testing revealed that the stand-alone cage with integrated screws provides more immediate stability than a cage alone and provides equivalent stability to ALIF constructs with supplemental fixation in lateral bending and axial rotation. Additional flexion-extension rigidity of the anterior cage maybe realized by the addition of a spinous process plate that was found to be as stable as supplemental bilateral PS.
No preview · Article · Jan 2013 · The spine journal: official journal of the North American Spine Society
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Apr 2012 · Journal of neurosurgery. Spine