title: A Novel, Minimally-Invasive Approach to Repair Degenerative Disk Disease in an Ovine Model Using Injectable Polymethyl-Methacrylate and Bovine Collagen (PMMA/BC).
abstract: BACKGROUND
  The natural, inflammatory repair processes of an injured intervertebral degenerative disc can propagate further injury and destruction. While there are many different treatment modalities of the pain related to degenerative disc disease, none are actually reparative in nature. Treatment strategies to repair a degenerative disc without inducing a destructive inflammatory milieu have been elusive.
  
  
  OBJECTIVE
  The purpose of this experiment is to discover the feasibility of reconstructing an injured intervertebral disc using an injected, inert polymer as the foundation for endogenous collagen growth.
  
  
  METHODS
  In this ovine model of six subjects in total, we introduce a modality where a large inert polymer, polymethyl methacrylate (PMMA), in conjunction bovine collagen (BC) is injected into the intervertebral disc. Following six months of observation, histologic specimens were evaluated macroscopically and microscopically for evidence of a benefit of the injectable PMMA/BC.
  
  
  METHODS
  We obtained six merino sheep for this study. Concentric injuries were made to four of their lumbar intervertebral discs. Two of those levels were treated with a percutaneous injection of 0.3 cc of PMMA/BC. The remaining lumbar levels were left untreated and were our controls. After six months, all subjects were sacrificed. Their four levels were extracted and were examined macroscopically and microscopically.
  
  
  RESULTS
  All subjects tolerated the lumbar injury and percutaneous injection of PMMA/BC well. After the six month interval, all subjects have demonstrated an intact architecture of their lumbar disc height at the macroscopic and microscopic level. Microscopically, there was no evidence of external migration of the PMMA/BC microspheres, nor was there any evidence of an inflammatory response by its presence. Notably, the PMMA/BC microspheres were well-incorporated into the concentric disc tears and had undergone endogenous collagen formation in its environment. Treatment levels were revealing for maintenance of disc height without evidence of an ongoing degeneration. The controlled levels were revealing for continued disc degeneration with loss of disc height and evolving injury at the level of the concentric tear.
  
  
  CONCLUSIONS
  This ovine model demonstrates a novel and promising technique for prevention and arrest of lumbar intervertebral disc degeneration.
authors.affiliation: Department of Neurosurgery, University of California, San Diego.
authors.forename: Reid
authors.initials: R
authors.lastname: Hoshide
authors.affiliation: Department of Neurosurgery, University of California, San Diego.
authors.forename: Erica
authors.initials: E
authors.lastname: Feldman
authors.affiliation: Department of Neurosurgery, University of California, San Diego.
authors.forename: Anisha
authors.initials: A
authors.lastname: Narayan
authors.affiliation: Department of Neurosurgery, University of California, San Diego.
authors.forename: William
authors.initials: W
authors.lastname: Taylor
keywords: degenerative disk disease; minimally invasive spine surgery; neurosurgery; orthopedic surgery