Technical ReportBiomechanical evaluation of an expandable meshed bag augmented with pedicle or facet screws for percutaneous lumbar interbody fusion
Introduction
Posterior lumbar interbody fusion and transforaminal lumbar interbody fusion (TLIF) have been widely used for the treatment of degenerative disc disease. Interbody implants such as structural bone grafts and interbody spacers may be biomechanically beneficial because of their proximity to the instantaneous axis of rotation, where they are loaded mainly in axial compression [1]. But either structural bone grafts or interbody cages need to be inserted into the disc space through a standard open approach or a minimally invasive tube that is much larger than the implant. The open posterior approach requires extensive dissection and retraction of paraspinous muscles and nerve roots. There may be complications associated with a greater blood loss, nerve injury, and persistent sequelae, such as muscular denervation, atrophy, and pain [2], [3]. To minimize the approach-related morbidities, numerous minimally invasive techniques for the lumbar spine have been developed and have become more popular. Minimally invasive techniques significantly reduce blood loss, postoperative pain, hospital stay, and narcotic usage [4], [5], [6], [7], [8], [9], [10].
Recently, a new device, referred to as the OptiMesh deployable grafting system (Spineology Inc., Saint Paul, MN, USA), has been developed to perform percutaneous lumbar interbody fusion using an expandable meshed bag filled with compacted granular bone graft. The expandable meshed bag is shown in Fig. 1. Compared with other minimally invasive techniques, the expandable mesh system requires smaller working channel and yet provides greater final graft size. It has been previously used in the treatment of vertebral compression fractures as an alternative to vertebroplasty or kyphoplasty [11], [12], [13]. For lumbar interbody fusion, the meshed bag serves as the interbody device providing structural support to the motion segment being fused. Limited clinical trials and early clinical results have shown that this technique is safe and effective [14]. However, no biomechanical data are available for a spinal segment treated with this new device. The objective of the present study was to evaluate the biomechanics of lumbar motion segments instrumented with stand-alone expandable meshed bag or meshed bag with posterior fixation using facet or pedicle screws and the efficacy of discectomy and disc distraction using the OptiMesh system. The spinal stability of the various surgical treatments and cage settling inside the disc space were measured.
Section snippets
Materials and methods
Twenty-four fresh-frozen human lumbar motion segments were harvested from nine human donors (five men and four women) with the age ranging from 54 to 70 years (average, 64±6.2 years). Specimens were dissected leaving all ligamentous structures intact. All specimens were screened via fluoroscopy to rule out any major anatomical abnormality (eg, fracture, pars defects, deformity, dysplasia, excessive osteophytes around the annulus, or congenital anomaly). Flexion extension (FE) moment was applied
Results
There was no bony defect or deformity in the specimen. The mean bone mineral density of the segments was 1.14±0.15 (standard deviation) g/cm2, which suggested moderate bone quality compared with the bone mineral density scores of young American adults. These results were common for patients older than 50 years.
The average ROM in AT, LB, and FE of the intact specimens and subsequent treatments are presented in Fig. 3. In the OptiMesh group, the mean ROM of all the intact specimens was 2.9°±1.8°,
Discussion
The OptiMesh bag knitted with polyethylene terephthalate thread is a hollow, seamless, deployable mesh container. After the bag is filled with granular bone graft material through a small access portal, further compaction of the graft can cause the granular material to change its phase from fluidic paste to rigid solid. The graft pack can serve as a structural support and withstand physiological compression loads without being squeezed back out through the access portal [13]. The access portal
Conclusions
In conclusion, stand-alone OptiMesh cannot provide adequate stability. Supplementary fixations including facet and pedicle screws are required to achieve higher construct stability for successful fusion. With anterior support by the expandable meshed bag, facet screws placed using the transfacet approach had comparable construct stability to that of pedicle screws. The distraction of the expandable meshed bag was limited. No noticeable meshed bag subsidence or collapse was measured after cyclic
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2016, Spine JournalCitation Excerpt :After the completion of the ROM testing, the implanted specimens were imaged via fluoroscopy to determine a baseline device position and repositioned into the load frame. The specimens were then subjected to a complex fatigue load cycle for 10,000 cycles, which is similar in length to other cadaveric fatigue studies and prevents complications from possible specimen degeneration [16–20]. This fatigue load cycle, including a 400 N preload, consisted of 5 Nm flexion-extension synchronized with axial torsion of 3 Nm at a frequency of approximately 1 Hz.
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2016, Clinical BiomechanicsCitation Excerpt :In our study we also found a greater mean stability with TFPS vs. PSR during axial rotation (Fig. 4), but without statistical significance (p = 0.219). Zheng et al. (2010) also reported no significant difference in the performance of facet screws vs. pedicle screws with TLIF in place regarding cage subsidence following cyclic in flexion–extension. We did not consider cage subsidence in the present study, but this would be an interesting focus of study.
Leveraging Compliance to Design a Minimally Invasive, Expandable Interbody Cage Capable of Customized Anatomical Fit for Spinal Fusion Surgery
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FDA device/drug status: not applicable.
Author disclosures: AAM (stock ownership, including options and warrants, Stryker, Medtronic; consulting, Stryker; research support: staff/materials, Medtronic; fellowship support, Medtronic, Synthes); EET (royalties, Medtronic; consulting, Medtronic; speaking/teaching arrangements, Stryker, Medtronic; scientific advisory board, United Health Care; fellowship support, Medtronic, Synthes Spine, Zimmer Spine).