Anterior Lumbar Interbody Fusion With Cement Augmentation Without Posterior Fixation to Treat Isthmic Spondylolisthesis in an Osteopenic Patient-A Surgical Technique

Methyl-Beta-Cyclodextrin Restores Aberrant Bone Morphogenetic Protein 2-Signaling in Bone Marrow Stromal Cells Obtained from Aged C57BL/6 Mice

During aging, disruptions in various signaling pathways become more common. Some older patients will exhibit irregular bone morphogenetic protein (BMP) signaling, which can lead to osteoporosis (OP)-a debilitating bone disease resulting from an imbalance between osteoblasts and osteoclasts. In 2002, the Food and Drug Administration (FDA) approved recombinant human BMP-2 (rhBMP-2) for use in spinal fusion surgeries as it is required for bone formation. However, complications with rhBMP-2 arose and primary osteoblasts from OP patients often fail to respond to BMP-2. Although patient samples are available for study, previous medical histories can impact results. Consequently, the C57BL/6 mouse line serves as a valuable model for studying OP and aging. We find that BMP receptor type Ia (BMPRIa) is upregulated in the bone marrow stromal cells (BMSCs) of 15-month-old mice, consistent with prior data. Furthermore, conjugating BMP-2 with Quantum Dots (QDot®s) allows effective binding to BMPRIa, creating a fluorescent tag for BMP-2. Furthermore, after treating BMSCs with methyl-β-cyclodextrin (MβCD), a disruptor of cellular endocytosis, BMP signaling is restored in 15-month-old mice, as shown by von Kossa assays. MβCD has the potential to restore BMPRIa function, and the BMP signaling pathway offers a promising avenue for future OP therapies.

Cyclic testing of standalone ALIF versus TLIF in lumbosacral spines of low bone mineral density: an ex vivo biomechanical study

PURPOSE

Screwed anterior lumbar interbody fusion (SALIF) alleviates the need for supplemental posterior fixation leading to reduction of perioperative morbidity. Specifically, elderly and multimorbid patients would benefit from shorter operative time and faster recovery but tend to have low bone mineral density (BMD). The current study aimed to compare loosening, defined as increase of ROM and NZ, of SALIF versus transforaminal lumbar interbody fusion (TLIF) under cyclic loading in cadaveric spines with reduced BMD.

METHODS

Twelve human spines (L4-S2; 6 male 6 female donors; age 70.6 ± 19.6; trabecular BMD of L5 84.2 ± 24.4 mgHA/cm3, range 51-119 mgHA/cm3) were assigned to two groups. SALIF or TLIF were instrumented at L5/S1. Range of motion (ROM) and neutral zone (NZ) were assessed before and after axial cyclic loading (0-1150 N, 2000 cycles, 0.5 Hz) in flexion-extension (Flex-Ext), lateral bending, (LB), axial rotation (AR).

RESULTS

ROM of the SALIF specimens increased significantly in all loading directions (p ≤ 0.041), except for left AR (p = 0.053), whereas for TLIF it increased significantly in left LB (p = 0.033) and Flex (p = 0.015). NZ of SALIF showed increase in Flex-Ext and LB, whereas NZ of TLIF did not increase significantly in any motion direction.

CONCLUSIONS

Axial compression loading caused loosening of SALIF in Flex-Ext and LB, but not TLIF at L5/S1 in low BMD specimens. Nevertheless, Post-cyclic ROM and NZ of SALIF is comparable to TLIF. This suggests that, neither construct is optimal for the use in patients with reduced BMD.

Impact of bone density and integrated screw configuration on standalone anterior lumbar interbody construct strength

Background

In anterior lumbar interbody fusion (ALIF), the use of integrated screws is attractive to surgeons because of the ease of implantation and no additional profile. However, the number and length of screws necessary for safe and stable implantation in various bone densities is not yet fully understood. The current study aims to determine how important both length and number of screws are for stability of ALIFs.

Methods

Three bone models with densities of 10, 15, and 20 pounds per cubic foot (PCF) were chosen as surrogates. These were instrumented using the Z-Link lumbar interbody system with either 2, 3, or 4 integrated 4.5 × 20 mm screws or 4.5 × 25 mm screws (Zavation, LLC, Flowood, MS). The bone surrogates were tested with loading conditions resulting in spine extension to measure construct stiffness and peak force.

Results

The failure load of the construct was influenced by the length of screws (p=.01) and density of the bone surrogate (p<.01). There was no difference in failure load between using 2 screws and 3 screws (p=.32) or when using four 20 mm screws versus three 25 mm screws (p=.295).

Conclusion

In our study, both bone density and length of screws significantly affected the construct's load to failure. In certain cases where a greater number of screws are unable to be implanted, the same stability can potentially be conferred with use of longer screws. Future clinical studies should be performed to test these biomechanical results.

Advances in Synthetic Grafts in Spinal Fusion Surgery

Degenerative spine disease is increasing in prevalence as the global population ages, indicating a need for targeted therapies and continued innovations. While autograft and allograft have historically demonstrated robust results in spine fusion surgery, they have significant limitations and associated complications such as infection, donor site morbidity and pain, and neurovascular injury. Synthetic grafts may provide similar success while mitigating negative outcomes. A narrative literature review was performed to review available synthetic materials that aim to optimize spinal fusion. The authors specifically address the evolution of synthetics and comment on future trends. Novel synthetic materials currently in use include ceramics, synthetic polymers and peptides, bioactive glasses, and peptide amphiphiles, and the authors focus on their success in both human and animal models, physical properties, advantages, and disadvantages. Advantages include properties of osteoinduction, osteoconduction, and osteogenesis, whereas disadvantages encompass a lack of these properties or growth factor-induced complications. Typically, the use of synthetic materials results in fewer complications and lower costs. While the development and tuning of synthetic materials are ongoing, there are many beneficial alternatives to autografts and allografts with promising fusion results.

Age-Related Low Bone Mineral Density in C57BL/6 Mice Is Reflective of Aberrant Bone Morphogenetic Protein-2 Signaling Observed in Human Patients Diagnosed with Osteoporosis

Osteoporosis (OP) is a bone disorder characterized by decreased bone mineral density (BMD). Bone Morphogenetic Protein-2 (BMP-2) injections are used to promote bone formation in OP patients. However, patients are unresponsive to BMP-2 while displaying an upregulation of BMP Receptor Type 1a (BMPRIa) and protein kinase CK2α (CK2α). A synthetically produced peptide named casein kinase 2.3 (CK2.3) utilizes the BMP-signaling pathway as it enhances osteogenesis of primary osteoblasts isolated from OP patients, whereas BMP-2 does not. Although shown in OP patients, there is currently no reliable mouse model to study BMP-2 and CK2.3 signaling. In this publication, we show that BMPRIa was required for CK2.3-mediated osteogenesis in C2C12 cells with a CRISPR-Cas9-mediated gene knockout for BMPRIa. We utilized the C57BL/6 (B6) mouse strain as an aging-model to study aberrant BMP-2 signaling, demonstrating that, like OP patients, in 15 and 20-month mice, BMP-2 did not increase bone growth and displayed upregulated BMPRIa and CK2α protein expression. Furthermore, CK2.3 enhanced osteogenesis and decreased osteoclastogenesis in all age groups, whereas BMP-2 only increased mineralization in 6-month mice while increasing osteoclast formation in all age groups. These data demonstrated that aging B6 mice were a reliable model and mimicked data obtained from OP patients.

[Comparative study of microscope assisted minimally invasive anterior fusion and mobile microendoscopic discectomy assisted fusion for lumbar degenerative diseases]

OBJECTIVE

To investigate the effectiveness of microscope assisted anterior lumbar discectomy and fusion (ALDF) and mobile microendoscopic discectomy assisted lumbar interbody fusion (MMED-LIF) for lumbar degenerative diseases.

METHODS

A clinical data of 163 patients with lumbar degenerative diseases who met the criteria between January 2018 and December 2020 was retrospectively analyzed. Fifty-three cases were treated with microscope assisted ALDF (ALDF group) and 110 cases with MMED-LIF (MMED-LIF group). There was no significant difference between the two groups in terms of gender, age, disease type, surgical segments, preoperative visual analogue scale (VAS) scores of low back pain and leg pain, Oswestry disability index (ODI), intervertebral space height, lordosis angle, and spondylolisthesis rate of the patients with lumbar spondylolisthesis ( P>0.05). The operation time, intraoperative blood loss, and hospital stay of the two groups were recorded. The effectiveness was evaluated by VAS scores of low back pain and leg pain and ODI. Postoperative lumbar X-ray films were taken to observe the position of Cage and measure the intervertebral space height, lordosis angle, and spondylolisthesis rate of the patients with lumbar spondylolisthesis.

RESULTS

The operations were successfully completed in both groups. The operation time, intraoperative blood loss, and hospital stay in ALDF group were less than those in MMED-LIF group ( P<0.05). The patients in both groups were followed up 12-36 months, with an average of 24 months. The VAS scores of low back pain and leg pain and ODI after operation were lower than those before operation in the two groups, and showed a continuous downward trend, with significant differences between different time points ( P<0.05). There were significant differences between two groups in VAS score of low back pain and ODI ( P<0.05) and no significant difference in VAS score of leg pain ( P>0.05) at each time point. The improvement rates of VAS score of low back pain and ODI in ALDF group were significantly higher than those in MMED-LIF group ( t=7.187, P=0.000; t=2.716, P=0.007), but there was no significant difference in the improvement rate of VAS score of leg pain ( t=0.556, P=0.579). The postoperative lumbar X-ray films showed the significant recovery of the intervertebral space height, lordosis angle, and spondylolisthesis rate at 2 days after operation when compared with preoperation ( P<0.05), and the improvements were maintained until last follow-up ( P>0.05). The improvement rates of intervertebral space height and lordosis angle in ALDF group were significantly higher than those in MMED-LIF group ( P<0.05). There was no significant difference in the reduction rate of spondylolisthesis between the two groups ( t=1.396, P=0.167). During follow-up, there was no loosening or breakage of the implant and no displacement or sinking of the Cage.

CONCLUSION

Under appropriate indications, microscope assisted ALDF and MMED-LIF both can achieve good results for lumbar degenerative diseases. Microscope assisted ALDF was superior to MMED-LIF in the improvement of low back pain and function and the recovery of intervertebral space height and lordosis angle.

Diagnostic, Surgical, and Technical Considerations for Lumbar Interbody Fusion in Patients with Osteopenia and Osteoporosis: A Systematic Review

Objective: Osteoporosis is increasing in incidence as the ageing population continues to grow. Decreased bone mineral density poses a challenge for the spine surgeon. In patients requiring lumbar interbody fusion, differences in diagnostics and surgical approaches may be warranted. In this systematic review, the authors examine studies performing lumbar interbody fusion in patients with osteopenia or osteoporosis and suggest avenues for future study. Methods: A systematic literature review of the PubMed and MEDLINE databases was performed for studies published between 1986 and 2020. Studies evaluating diagnostics, surgical approaches, and other technical considerations were included. Results: A total of 13 articles were ultimately selected for qualitative analysis. This includes studies demonstrating the utility of Hounsfield units in diagnosis, a survey of surgical approaches, as well as exploring the use of vertebral augmentation and cortical bone screw trajectory. Conclusions: This systematic review provides a summary of preliminary findings with respect to the use of Hounsfield units as a diagnostic tool, the benefit or lack thereof with respect to minimally invasive approaches, and the question of whether or not cement augmentation or cortical bone trajectory confers benefit in osteoporotic patients undergoing lumbar interbody fusion. While the findings of these studies are promising, the current state of the literature is limited in scope and, for this reason, definitive conclusions cannot be drawn from these data. The authors highlight gaps in the literature and the need for further exploration and study of lumbar interbody fusion in the osteoporotic spine.

Medicare Utilization and Reimbursement for Vertebroplasty and Kyphoplasty: A National Analysis From 2012-2017

STUDY DESIGN

Retrospective cohort study OBJECTIVE.: This study seeks to identify recent trends in utilization and reimbursements of these procedures between 2012and 2017, a period which experienced a change in national guideline recommendations for these procedures.

SUMMARY OF BACKGROUND DATA

Minimally invasive vertebral augmentation procedures, including vertebroplasty and kyphoplasty, have been typically reserved for fractures associated with refractory pain, deformity, or progressive neurological symptoms. However, controversy exists regarding the safety and effectiveness of these procedures, in particular vertebroplasty.

METHODS

Annual Medicare claims and payments to surgeons were aggregated at the county level to assess regional trends. Descriptive statistics and multivariate regression models were used to evaluate trends in procedure volume, utilization rates, and reimbursement rates, and to examine associations between county-specific variables and outcome variables.

RESULTS

A total of 24,316 vertebroplasties and 138,778 kyphoplasties were performed in the Medicare population between 2012 and 2017. Annual vertebroplasty volume fell by 48.0% from 5744 procedures in 2012 to 2987 in 2017, with a compound annual growth rate (CAGR) of -12.3%. Annual kyphoplasty volume also declined by 12.7% (CAGR -2.7%), from 24,986 in 2012 to 21,681 in 2017. Surgeon reimbursements for vertebral augmentation procedures increased by a weighted average of 93.7% (inflation-adjusted increase of 78.2%) between 2012 and 2017, which was primarily driven by a dramatic 113.3% (inflation-adjusted increase of 96.2%) increase in mean reimbursements for kyphoplasty procedures from an average of $895 to $1764, between 2012 and 2017, respectively.

CONCLUSION

This large national Medicare database study found that vertebroplasty and kyphoplasty procedure volume and utilization of both procedures have declined significantly. Although average reimbursements to surgeons for vertebroplasties have significantly declined, payments for kyphoplasty procedures have risen significantly. Although vertebroplasty volume has significantly decreased, it is still being performed and being reimbursed for, in spite of its controversial role in its treatment of vertebral fractures.

LEVEL OF EVIDENCE

3.