P22. Lumbar intervertebral spacer with cement augmentation of endplates and integrated screws as a fixation device in an osteoporotic model: an in vitro kinematic and load-to-failure study

Abstract

BACKGROUND CONTEXT Integrated LLIF stabilizes the spine and avoids complications related to posterior fixation. However, contraindications such as low bone mineral density (BMD) and older age can increase risk of subsidence. Traditional cement augmentation through cannulated pedicle screws enhances pedicle fixation and cage-endplate interface, yet may be disadvantageous due to associated paraspinal dissection, blood loss, and iatrogenic infection. Nevertheless, cement augmentation may be sufficient in preventing subsidence of stand-alone LLIF reconstructions in elderly patients. The lateral application of cement with integrated LLIF fixation has been introduced and requires kinematic and failure characterizations. PURPOSE To evaluate kinematic and load-to-failure properties of a novel cement augmentation technique with an integrated lateral lumbar interbody fusion (LLIF) device, both alone and with unilateral pedicle fixation, in comparison with bilateral pedicle screws and non-integrated LLIF (BPS+S). STUDY DESIGN/SETTING In vitrohuman cadaveric study. PATIENT SAMPLE 12 cadaveric specimens. OUTCOME MEASURES Range of motion (ROM) and ultimate load to failure. METHODS Twelve specimens (L3–S1) underwent discectomy (L4–L5). Specimens were separated into 3 groups: (1) BPS+S, (2) polymethylmethacrylate (PMMA), integrated LLIF, and unilateral pedicle screws. (PMMA+UPS+iS), and (3) PMMA with iSA (PMMA+iSA). Before LLIF insertion, a vertebroplasty needle inserted 3mm deep from the endplate at the vertical midline of the vertebral body (VB). The needle was repeatedly inserted through the cancellous bone, creating a cavity deep to the endplate. PMMA (3cc) was injected into the cavity, limited to approximately 25% of the operative endplates, followed by insertion of the LLIF device. After cement curing, flexion-extension, lateral bending and axial rotation were applied. Finally, a compressive load was applied to the segments until failure to assess spacer-endplate strength. RESULTS No significant differences in BMD T-scores between BPS+S (-1.9±0.7), PMMA+UPS+iS (-1.8±0.5), and PMMA+iS (-1.8±0.7) groups were observed (P = 0.992). Operative constructs significantly reduced motion relative to intact specimens in all motion planes (P 0.05). PMMA+UPS+iS provided the greatest resistance to failure (2290 N), followed by PMMA+iSA (1970 N), and lastly, BPS+S (1390 N); no significant differences were observed (P > 0.05). CONCLUSIONS A novel technique of vertebral endplate cement augmentation via the lateral approach with an integrated interbody device for osteoporotic patients who would otherwise require posterior fixation to reduce likelihood of subsidence is proposed. The integrated lateral interbody spacer with vertebral endplate cement augmentation, both prior to and following unilateral pedicle fixation, was biomechanically equivalent to traditional anteroposterior fixation with non-integrated LLIF. The integrated device with cement augmentation moderately improved spacer-endplate interface compared to BPS+S in an osteoporotic model, increasing failure loads compared by 41.7%; the addition of unilateral fixation further increased resistance to failure (64.7%). Overall, results suggest integrated LLIF with cement may be a viable alternative in the presence of osteoporosis. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.