Contained-Delivery Route and the Administration of Postoperative Steroids Following Anterior Cervical Spinal Fusion With Low-dose rhBMP-2 Reduces the Magnitude of Respiratory Compromise

Local drug delivery challenges and innovations in spinal neurosurgery

The development of novel therapeutics in the field of spinal neurosurgery faces a litany of translational challenges. Achieving precise drug targeting within the confined spaces associated with the spinal cord, canal and vertebra requires the development of next generation delivery systems and devices. These must be capable of overcoming inherent barriers related to drug diffusion, whilst concurrently ensuring optimal drug distribution and retention. In this review, we provide an overview of the most recent advances in the therapeutic management of diseases and disorders affecting the spine, including systems and devices capable of releasing small molecules and biopharmaceuticals that help eliminate pain and restore the mechanical function and stability of the spine. We highlight material-based approaches and minimally invasive techniques that can be employed to provide control over drug release kinetics and improve retention. We also seek to explore how the newest advancements in nanotechnology, biomaterials, additive manufacturing technologies and imaging modalities can be employed in this translational pursuit. Finally, we discuss the landscape of clinical trials and recently approved products aimed at overcoming the complexities associated with drug delivery to the spine.

The incidence of reoperation for pseudarthrosis after cervical spine surgery

INTRODUCTION

Pseudarthrosis after cervical spine surgery represents an underreported and challenging complication. Using a large multi-center surgical database, we sought to: (1) report the incidence of cervical pseudarthrosis, (2) evaluate changes in rates of cervical pseudarthrosis, and (3) describe risk factors for suboptimal outcomes after cervical pseudarthrosis surgery.

METHODS

The American College of Surgeons National Surgical Quality Improvement Program database from 2012 to 2019 was used. The primary outcome was occurrence of a cervical fusion procedure with a prior diagnosis of pseudarthrosis. Fusion for pseudarthrosis was divided into anterior and posterior approaches. Post-operative complications were classified as major or minor. Prolonged LOS was defined as exceeding the 75th percentile for total hospital stay.

RESULTS

A total of 780 patients underwent cervical fusion for pseudarthrosis, and a significant increase in rates of surgery for pseudarthrosis was seen (0.25-1.2%, p < 0.001). The majority of cervical pseudarthrosis was treated with a posterior approach (66.5%). Postoperatively, 38 (4.9%) patients suffered a complication and 247 (31.7%) had a prolonged LOS. The three strongest risk factors for complications and extended LOS were > 10% weight loss preoperatively, congestive heart failure, and pre-operative bleeding disorder.

CONCLUSION

Results from a large multi-center national database revealed that surgery to treat cervical pseudarthrosis has increased from 2012 to 2019. Most pseudarthrosis was treated with a posterior approach. Reoperation to treat cervical pseudarthrosis carried risk, with 5% having complications and 32% having an extended LOS. These results lay the groundwork for a future prospective study to discern the true incidence of cervical pseudarthrosis and how to best avoid its occurrence.

Meta-Analysis on Efficacy and Complications of Bone Morphogenetic Protein-2 for Posterior Fusion of Cervical Spine

OBJECTIVE

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is effective for promoting robust fusion for long-level cervical deformity and revision surgeries. However, only a few studies have reported its efficacy and complications in posterior cervical fusion (PCF).

METHODS

Therefore we evaluated the efficacy and complications of rhBMP-2 application in PCF surgery by searching 3 electronic databases (PubMed, Cochrane Database, and EMBASE) for studies that evaluated the use of rhBMP-2 in PCF. Five studies (1 prospective and 4 retrospective) were included in the meta-analysis.

RESULTS

The quality of each study was assessed, and data on pseudarthrosis, wound infection, neurologic, and immediate medical complications were extracted and analyzed. We found that the use of rhBMP-2 in PCF showed significant benefits in terms of pseudarthrosis and no significant increases in the risk for neurologic and immediate medical complications regardless of the dose. However, high-dose (>2.1 mg/level) rhBMP-2 was a risk factor for wound infection after PCF.

CONCLUSIONS

Our meta-analysis of the currently available literature suggests that patients with PCF may benefit from BMP-2 usage without increasing the risk of complications. However, dose control and containment are important to ensure a low risk of complications.

Comparative Complications Associated With BMP Use In Patients Undergoing ACDF for Degenerative Spinal Conditions: Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic Review and Meta-Analysis.

OBJECTIVES

To compare complication incidence in patients with or without the use of recombinant human Bone Morphogenic Protein-2 (BMP2) undergoing anterior cervical discectomy and fusion (ACDF) for degenerative conditions.

METHODS

A systematic search of eight online databases was conducted using PRISMA guidelines. Inclusion criteria included English language studies with a minimum of 10 adult patients undergoing instrumented ACDF surgery for a degenerative spinal condition in which BMP2 was used in all patients or one of the treatment arms. Studies with patients undergoing circumferential fusions, with non-degenerative indications, or which did not report post-operative complication data were excluded. Patients with and without BMP2 were compared in terms of the incidence of dysphagia/dysphonia, anterior soft tissue complications (hematoma, seroma, infection, dysphagia/dysphonia), nonunion, medical complications, and new neurologic deficits.

RESULTS

Of 1832 preliminary search results, 27 manuscripts were included. Meta-analysis revealed the relative risk of dysphagia or dysphonia (RR = 1.39, CI 95% 1.18 - 1.64, P = <.001), anterior soft tissue complications (RR = 1.43, CI 95% 1.25-1.64, P = <.001), and medical complications (RR = 1.32, CI 95% 1.06-1.66, P = .013) were statistically significant in the BMP2 group while the relative risk of non-union (RR = .5, CI 95% .23 - 1.13, P = .09) trended lower in the BMP2 group. Neurological deficit (RR = 1.06, CI 95% .82-1.37, P = .66), and additional medical complications (RR = 1.53, CI 95% .98-2.38, P = .06) were not found to be statistically different between the groups.

CONCLUSIONS

This meta-analysis identified a high rate of arthrodesis when BMP2 was used in ACDF, but confirmed increased rates of dysphagia and anterior soft tissue complications. Surgeons may consider reserving BMP2 implementation for cases with a high risk of non-union, and should be aware of the risk of airway compromise.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

Airway Complications After Anterior Cervical Spine Surgery: Etiology and Risk Factors

STUDY DESIGN

Narrative Review.

OBJECTIVE

To provide an overview of etiology and risk factors of airway complications after anterior cervical spine surgery (ACSS).

METHODS

A search was performed in PubMed and adapted for use in other databases, including Embase, Cochrane Library, Cochrane Register of Controlled Trials, Health Technology Assessment database, and NHS Economic Evaluation Database.

RESULTS

81 full-text studies were reviewed. A total of 53 papers were included were included in the review and an additional four references were extracted from other references. 39 papers were categorized as etiology and 42 as risk factors.

CONCLUSIONS

Most of the literature on airway compromise after ACSS is level III or IV evidence. Currently, there are no systems in place to risk-stratify patients undergoing ACSS regarding airway compromise or guidelines on how to manage patients when these complications do occur. This review focused on theory, primarily etiology and risk factors.

Safety and efficacy of low-dose rhBMP-2 use for anterior cervical fusion

OBJECTIVE

The use of recombinant human bone morphogenetic protein 2 (rhBMP-2) in routine anterior cervical fusion (ACF) is controversial. Early reports described high complication rates. A variety of dosing regimens ranging from 0.6 to 2.1 mg per level fused have been reported. The authors hypothesized that the high amounts of rhBMP-2 used in these studies led to the high complication rates observed; therefore, they set out to evaluate the safety and efficacy of low-dose rhBMP-2 for use in ACFs.

METHODS

Patient inclusion criteria were 1) age 18 to 70 years; 2) initial stand-alone ACF construct; 3) fusion augmentation with rhBMP-2; and 4) at least 1 year of radiographic follow-up. A successful fusion was defined by either 1) lateral flexion-extension radiographs with less than 1 mm of movement across the fused spinous processes, or 2) bone bridging at least half of the fusion area originally achieved by surgery on fine-cut CT. Patient demographics, perioperative data, and postoperative complications were recorded.

RESULTS

A total of 198 patients met the inclusion criteria and were included for analysis. Sixty-two patients (31%) were smokers. The median number of levels fused was 2 (IQR 1.25). The mean dose of rhBMP-2 was 0.50 ± 0.09 mg per level. Twenty-two (11%) patients experienced dysphagia. Eleven (6%) patients experienced cervical swelling. Two (1%) patients returned to the operating room (OR) for postoperative hematoma. One (0.5%) patient returned to the OR for seroma. Two (1%) patients experienced pseudarthrosis requiring a posterior fusion. Three (2%) patients experienced a new postoperative neurological deficit that had recovered by last the follow-up. Overall, 190 (96%) patients experienced solid arthrodesis over an average of 15 months of follow-up. There was no difference in fusion rates between patients who were either smokers or nonsmokers (p = 0.7073).

CONCLUSIONS

The use of low-dose rhBMP-2 safely and effectively augmented anterior cervical arthrodesis. The low-dose protocol assessed in this study appeared to significantly reduce complications associated with rhBMP-2 use in ACF compared with the literature. The authors have determined that using low-dose rhBMP-2 in patients who are smokers, those with multilevel ACFs, or others at high risk of developing pseudarthrosis is recommended.

BMP and TGFβ use and release in bone regeneration

A fracture that does not unite in nine months is defined as nonunion. Nonunion is common in fragmented fractures and large bone defects where vascularization is impaired. The distal third of the tibia, the scaphoid bone or the talus fractures are furthermore prone to nonunion. Open fractures and spinal fusion cases also need special monitoring for healing. Bone tissue regeneration can be attained by autografts, allografts, xenografts and synthetic materials, however their limited availability and the increased surgical time as well as the donor site morbidity of autograft use, and lower probability of success, increased costs and disease transmission and immunological reaction probability of allografts oblige us to find better solutions and new grafts to overcome the cons. A proper biomaterial for regeneration should be osteoinductive, osteoconductive, biocompatible and mechanically suitable. Cytokine therapy, where growth factors are introduced either exogenously or triggered endogenously, is one of the commonly used method in bone tissue engineering. Transforming growth factor β (TGFβ) superfamily, which can be divided structurally into two groups as bone morphogenetic proteins (BMPs), growth differentiation factors (GDFs) and TGFβ, activin, Nodal branch, Mullerian hormone, are known to be produced by osteoblasts and other bone cells and present already in bone matrix abundantly, to take roles in bone homeostasis. BMP family, as the biggest subfamily of TGFβ superfamily, is also reported to be the most effective growth factors in bone and development, which makes them one of the most popular cytokines used in bone regeneration. Complications depending on the excess use of growth factors, and pleiotropic functions of BMPs are however the main reasons of why they should be approached with care. In this review, the Smad dependent signaling pathways of TGFβ and BMP families and their relations and the applications in preclinical and clinical studies will be briefly summarized.