Intraoperative chymopapain in lumbar laminotomy for disc disease: a less invasive technique

Gene Therapy and Spinal Fusion: Systematic Review and Meta-Analysis of the Available Data

OBJECTIVE

To analyze the extant literature describing the application of gene therapy to spinal fusion.

METHODS

A systematic review of the English-language literature was performed. The search query was designed to include all published studies examining gene therapy approaches to promote spinal fusion. Approaches were classified as ex vivo (delivery of genetically modified cells) or in vivo (delivery of growth factors via vectors). The primary endpoint was fusion rate. Random effects meta-analyses were performed to calculate the overall odds ratio (OR) of fusion using a gene therapy approach and overall fusion rate. Subgroup analyses of fusion rate were also performed for each gene therapy approach.

RESULTS

Of 1179 results, 35 articles met criteria for inclusion (all preclinical), of which 26 utilized ex vivo approaches and 9 utilized in vivo approaches. Twenty-seven articles (431 animals) were included in the meta-analysis. Gene therapy use was associated with significantly higher fusion rates (OR 77; 95% confidence interval {CI}: [31, 192]; P < 0.001); ex vivo strategies had a greater effect (OR 136) relative to in vivo strategies (OR 18) (P = 0.017). The overall fusion rate using a gene therapy approach was 80% (95% CI: [62%, 93%]; P < 0.001); overall fusion rates were significantly higher in subjects treated with ex vivo compared to in vivo strategies (90% vs. 42%; P = 0.011). For both ex vivo and in vivo approaches, the effect of gene therapy on fusion was independent of animal model.

CONCLUSIONS

Gene therapy may augment spinal fusion; however, future investigation in clinical populations is necessary.

An injectable method for noninvasive spine fusion

BACKGROUND CONTEXT

Bone morphogenetic proteins (BMPs) induce bone formation but are difficult to localize, and subsequent diffusion from the site of interest and short half-life reduce the efficacy of the protein. Currently, spine fusion requires stripping, decortications of the transverse processes, and an autograft harvest procedure. Even in combination with BMPs, clinical spinal fusion has a high failure rate, presumably because of difficulties in localizing sufficient levels of BMP.

PURPOSE

The goal was to achieve reliable spine fusion through a single injection of a cell-based gene therapy system without the need for any surgical intervention.

STUDY DESIGN

Eighty-seven immunodeficient (n=44) and immune-competent (n=43) mice were injected along the paraspinous musculature to achieve rapid induction of heterotopic ossification (HO) and ultimately spinal arthrodesis.

METHODS

Immunodeficient and immune-competent mice were injected with fibroblasts, transduced with an adenoviral vector to express BMP2, along the paraspinous musculature. Bone formation was evaluated via radiographs, microcomputed tomography, and biomechanical analysis.

RESULTS

ew bridging bone between the vertebrae and the fusion to adjacent skeletal bone was obtained as early as 2 weeks. Reduction in spine flexion-extension also occurred as early as 2 weeks after injection of the gene therapy system, with greater than 90% fusion by 4 weeks in all animals regardless of their genetic background.

CONCLUSIONS

Injection of our cell-based system into the paraspinous musculature induces spinal fusion that is dependent neither on the cell type nor on the immune status. These studies are the first to harness HO in an immune-competent model as a noninvasive injectable system for clinically relevant spinal fusion and may one day impact human spinal arthrodesis.

Genetically engineered mesenchymal stem cells: applications in spine therapy

Spine disorders and intervertebral disc degeneration are considered the main causes for the clinical condition commonly known as back pain. Spinal fusion by implanting autologous bone to produce bony bridging between the two vertebrae flanking the degenerated-intervertebral disc is currently the most efficient treatment for relieving the symptoms of back pain. However, donor-site morbidity, complications and the long healing time limit the success of this approach. Novel developments undertaken by regenerative medicine might bring more efficient and available treatments. Here we discuss the pros and cons of utilizing genetically engineered mesenchymal stem cells for inducing spinal fusion. The combination of the stem cells, gene and carrier are crucial elements for achieving optimal spinal fusion in both small and large animal models, which hopefully will lead to the development of clinical applications.

Human mesenchymal stem cells transduced with recombinant bone morphogenetic protein-9 adenovirus promote osteogenesis in rodents

The present study was undertaken to determine whether ex vivo bone morphogenetic protein-9 (BMP-9) gene therapy using human mesenchymal stem cells (hMSCs) can induce endochondral bone formation in athymic nude rats. An in vitro study was initially performed on hMSCs to evaluate morphological changes and osteoblastic differentiation induced by replication-defective adenovirus type 5 with the cytomegalovirus promoter and either the BMP-9 (Ad-BMP-9) or beta-galactosidase (Ad-beta-gal) gene. In vivo, athymic nude rats received an injection (10(6) hMSCs transduced with recombinant adenovirus at 50 PFU/cell) into the anterior thigh musculature: Ad-BMP-9 on the left and Ad-beta-gal (control) on the right. Computed tomography scans and histological analysis were obtained 7, 14, 28, 42, 56, and 84 days postinjection. In vitro, human mesenchymal stem cells treated with Ad-BMP-9 (50 PFU/cell) showed signs of differentiation, whereas hMSCs treated with 250 and 1250 PFU/cell showed cytotoxicity. In vivo, computed tomography and histological analysis clearly demonstrated ectopic bone at hMSC/Ad-BMP-9 treatment sites, whereas the hMSC/Ad-beta-gal treatment sites showed no evidence of osteogenesis. None of the animals showed clinical evidence of toxicity. Ex vivo gene therapy with hMSC/BMP-9 may be efficacious for promoting bone formation for a variety of bone pathologies and certainly warrants further investigations.

Secondary gain influences the outcome of lumbar but not cervical disc surgery

BACKGROUND

The expectation of monetary compensation has been associated with poor outcomes in lumbar discectomy, fueling a reluctance among surgeons to treat worker's compensation cases. This issue, however, has not been investigated in patients undergoing cervical disc surgery. This study analyzes the relationship between economic forms of secondary gain and surgical outcome in a group of patients with common pay scales, retirement plans, and disability programs.

METHODS

All procedures were performed at the Portsmouth Naval Medical Center between 1993 and 1995; active duty military servicepersons who were treated for cervical radiculopathy were prospectively included. Clinical, demographic, and financial factors were analyzed to determine which were predictive for outcome. Financial data were used to create a compensation incentive (CI) which is proportional to the rank, years of service, potential disability, retirement eligibility, and base pay and reflects the monetary incentive of disability. The results of cervical surgery were compared to a previously reported companion population of patients treated for lumbar disc disease. A good outcome is defined as a return to active duty, whereas a referral for disability is considered a poor surgical result.

RESULTS

One hundred percent follow-up was obtained for 269 patients who were treated with 307 cervical operations. Only 16% (43/269) of cervical patients received disability, whereas 24.7% (86/348) of lumbar patients obtained a poor result (p = 0.0082). Although economic forms of secondary gain were not associated with outcome in cervical disease, both the position (p = 0.002) and duration of an individual's military career were significant factors (p = 0.02). Of the medical variables tested, multilevel surgery (p = 0.03) and revision operations at the same level (p = 0.03) were associated with referral for medical discharge.

CONCLUSIONS

Secondary gain in the form of economic compensation influences outcome in lumbar but not cervical disc surgery; this observation may in part account for the success of cervical surgery relative to lumbar discectomy. Social factors that are independent of the anticipation of economic compensation seem to influence the outcome of cervical disc surgery.