Percutaneous Gene-Delivery Mediated Intervertebral Body Fusion-Young Investigator Grant
Matthew E. Cunningham, MD, PhD; Oheneba Boachie-Adjei, MD
PURPOSE: Anterior spinal fusions (ASFs) provide excellent arthrodesis rates and mechanical stability; however, associated complications (visceral injuries, DVT, incisional pain, abdominal wall herniations/weakness) can be catastrophic. A potential alternative to traditional ASF surgery is percutaneous delivery of osteogenic cues to the intervertebral disk space (IVD) that can drive bone formation and spine fusion while minimizing surgical risk. We have developed a rat model for minimally invasive anterior spine fusions, with preliminary findings of fusion bone production outside of and anterior to the disk space, and fusions in 31-75% of levels in the most responsive test group. The technique has great promise to deliver a method for human percutaneous anterior spine fusions. Optimization of the model is required to improve fusion rates and to drive bone formation within the disk space.
HYPOTHESIS: (1) Vascular Endothelial Growth Factor (VEGF) has been demonstrated to increase bone production in bone morphogenetic protein (BMP) induced bone formation. We hypothesize that addition of VEGF to the BMPs delivered in our model will augment bone production and increase fusion rates. (2) Interleukin-1-beta (IL-1b) has been shown to induce chondroid matrix degrading enzymes in cultured human disk cells, and these chondroid matrix degrading enzymes are associated with degenerative disk disease and fragment degradation after herniations. We hypothesize that addition of the IL-1b to the BMPs delivered in our model will cause digestion of the disk material, and will allow bone production within the disk space. In addition, driving bone formation within the disk space may cause fusion rates to improve. This is due to the smaller quantity of bone required to bridge endplates within the disk, than bone formation required to bridge vertebral bodies outside of the disk space.
METHODS: The minimally invasive rat model we have developed delivers marrow stromal cells, genetically modified with adenoviral vectors containing marker genes or BMPs, to the prepared L4/5 and L5/6 disk spaces. Lewis rats are utilized to eliminate immune/rejection confounding artifacts. Standard tissue culture techniques are used to establish primary cultures of bone marrow stromal cells, to propogate and expand the cultures, and to undergo genetic modification. Outcomes assessed are dynamic faxitron motion quantification in time course, fusion status by radiology and palpation, biomechanical analysis to assess fusion strength, micro-CT to quantify bone formation, and histology to characterize bone quality and vascularization.
In-vivo Spine Biomechanics: Application of an Innovative Combined MR and Dual Fluoroscopic Imaging Technique
Kirkham B. Wood, MD; Guoan Li, Ph
Lower back pain secondary to degenerative changes in the lumbar spine is an extremely common condition. To understand the biomechanical factors that affect spinal pathology, it is critical to quantitatively understand the spinal structure function under in-vivo loading conditions. However, very little data has been reported on vertebral motion in 6 degree-of-freedom (DOF) in living subjects. This study will utilize a novel combined dual orthogonal fluoroscopic and magnetic resonance imaging technique to accurately investigate in-vivo spine joint kinematics and interface soft-tissue deformation non-invasively. Magnetic resonance imaging will be performed to create three-dimensional vertebral models. Two fluoroscopes will be positioned orthogonally to capture vertebral motion of living subjects during various postures simultaneously. The captured fluoroscopic images and the models will be matched to reproduce the actual 6 DOF vertebral kinematics. Furthermore, the 3D intervertebral disc deformation, the apophyseal joint articular contact, and the ligament elongation will be measured. We hypothesize that the analysis of relative motion between vertebras will allow us to quantitatively understand in-vivo lumbar spine structural function. The data will provide base-line information on normal spine function, thus to help improve the diagnosis and treatment of pain secondary to spinal degeneration. The long-term benefits would include innovations in surgical technique and implant design, which would ultimately lead to an overall improvement in patient quality of life. Our laboratory has already conducted validation studies on an ovine lumbar spine and the results have demonstrated that the in-vivo spine kinematics can be accurately determined using this imaging technique.
Biological Repair of Intervertebral Disc Degeneration
Fackson Mwale, PhD; John Antoniou, MD, PhD; Peter Roughley
Degenerative disc disease has been implicated as a major component of spine pathology. Currently, the two major clinical procedures for treating disc degeneration are disc excision and spinal fusion. Although these procedures offer relatively good short-term clinical results in relief of pain, in many instances, these treatment modalities have been disappointing because of altered spinal mechanics leading to subsequent degeneration at adjacent disc levels. Biological repair of the degenerated disc would be the ideal treatment and recent advances in tissue engineering offer the unique opportunity to repair a nucleus pulposus using polymer-cell constructs and growth factors. The long term goal is to promote nucleus pulposus repair in the degenerated intervertebral disc. We hypothesized that the injection of link N, a natural peptide with growth factor properties, in the presence of stem cells can stimulate the repair of the degenerated intervertebral disc in Thomson grades 2 and 3 discs. In the present study, we will specifically use a rabbit model of degenerated disc in which different combinations of mesenchymal stem cells/link N/polymer scaffold will be injected. The effect of these treatments will be analyzed by histology, extracellular matrix composition, and expression of collagens and aggrecan genes. We expect that link N, used as growth factor, will promote disc repair, that the repair initiated by mesenchymal stem cells will be enhanced by link N, and that chitosan, a biocompatible injectable polymer gelling at 37 degrees Celsius, will further enhance repair.
Proinflammatory Cytokine Profile of Intervertebral Disc Tissues from Patients with Discogenic Axial Back Pain Confirmed by Discography
Yejia Zhang, MD, PhD; D. Greg Anderson, MD
Back pain affects millions of people around the world and has an enormous socio-economic impact. Diagnosis and treatment of axial back pain is particularly challenging, because pain is not well correlated with intervertebral disc degeneration: most individuals with disc degeneration are not affected by chronic symptoms. Furthermore, patients affected by chronic discogenic axial back pain rarely achieve complete relief from the available medical therapies. The search for better therapies for this pervasive disease is hampered by poor understanding of the disease mechanism and lack of biological markers.
Kang and others have reported increased cytokine production in herniated discs. Although these findings help the understanding of neurogenic leg pain associated with disc herniation, they do not necessarily translate into axial discogenic pain, which is different in character and less responsive to current treatments. A better understanding of the underlying pathophysiology for discogenic axial back pain is needed to facilitate the development of targeted therapies for this prevalent disease.
Our group has obtained Institutional Review Board (IRB) approved access to surgically-removed intervertebral disc tissues from patients with well documented preoperative discography (both positive and negative studies). Using highly sensitive antibody arrays, we have demonstrated our ability to measure the levels of a panel of cytokines and have found specific differences in cytokine levels between a symptomatic disc (positive discography) from a patient with discogenic axial back pain, and an asymptomatic disc (negative discography, as control) from a patient with scoliosis; both discs studied are severely degenerative, grade V by magnetic resonance images (MRIs) according to the Pfirrmann grading scheme. Based on these findings, we hypothesize that disc tissues from symptomatic levels (positive discography) contain increased levels of specific cytokines that will serve as biomarkers and targets for biologic therapies for discogenic axial back pain. In this pilot study, we have proposed to collect and characterize intervertebral disc tissues from patients with clear cut discogenic back pain (as confirmed by careful discography). Patients with neurogenic leg pain as a result of disc herniation will be excluded. Control discs from patients with no history of back pain or negative pain by discography will also be collected (typically removed during surgery for spinal deformity). In some cases, symptomatic and asymptomatic discs will be obtained from the same patients requiring interbody reconstruction for a spinal deformity. All discs will be graded according to Pfirrmann et al, and comparisons will be made between painful and painless discs with the same degree of degeneration. Then, using a human cytokine antibody array that enables the simultaneous detection of multiple cytokines in one assay, we will semiquantatively compare levels of cytokines in painful discs with those in control discs. To further quantify selected cytokines, the tissues will be studied using a custom multiplex cytokine assay ( a sandwich immunoassay-based multiplex protein array system).
In summary, we will carefully catalogue the cytokine profiles of symptomatic and control discs of the same MRI grades, in order to define biomarkers for discogenic back pain and to identify targets for future biologic therapies.