title: An injectable nucleus pulposus implant restores compressive range of motion in the ovine disc.
abstract: METHODS
  Investigation of injectable nucleus pulposus (NP) implant.
  
  
  OBJECTIVE
  To assess the ability of a recently developed injectable hydrogel implant to restore nondegenerative disc mechanics through support of NP functional mechanics.
  
  
  BACKGROUND
  Although surgical intervention for low back pain is effective for some patients, treated discs undergo altered biomechanics and adjacent levels are at increased risk for accelerated degeneration. One potential treatment as an alternative to surgery for degenerated disc includes the percutaneous delivery of agents to support NP functional mechanics. The implants are delivered in a minimally invasive fashion, potentially on an outpatient basis, and do not preclude later surgical options. One of the challenges in designing such implants includes the need to match key NP mechanical behavior and mimic the role of native nondegenerate NP in spinal motion.
  
  
  METHODS
  The oxidized hyaluronic acid gelatin implant material was prepared. In vitro mechanical testing was performed in mature ovine bone-disc-bone units in 3 stages: intact, discectomy, and implantation versus sham. Tested samples were cut axially for qualitative structural observations.
  
  
  RESULTS
  Discectomy increased axial range of motion (ROM) significantly compared with intact. Hydrogel implantation reduced ROM 17% (P < 0.05) compared with discectomy and returned ROM to intact levels (ROM intact 0.71 mm, discectomy 0.87 mm, postimplantation 0.72 mm). Although ROM for the hydrogel implant group was statistically unchanged compared with the intact disc, ROM for sham discs, which received a discectomy and no implant, was significantly increased compared with intact. The compression and tension stiffness were decreased with discectomy and remained unchanged for both implant and sham groups as expected because the annulus fibrosus was not repaired. Gross morphology images confirmed no ejection of NP implant.
  
  
  CONCLUSIONS
  An injectable implant that mimics nondegenerate NP has the potential to return motion segment ROM to normal subsequent to injury.
authors.affiliation: Department of Neurological Surgery, University of Pennsylvania, Philadelphia PA 19106, USA. neil.malhotra@uphs.upenn.edu
authors.forename: Neil R
authors.initials: NR
authors.lastname: Malhotra
authors.forename: Woojin M
authors.initials: WM
authors.lastname: Han
authors.forename: Jesse
authors.initials: J
authors.lastname: Beckstein
authors.forename: Jordan
authors.initials: J
authors.lastname: Cloyd
authors.forename: Weiliam
authors.initials: W
authors.lastname: Chen
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Elliott
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D017586:Diskectomy / Q000379:methods; D005780:Gelatin / Q000008:administration & dosage; D006801:Humans; D006820:Hyaluronic Acid / Q000008:administration & dosage / Q000737:chemistry; D007403:Intervertebral Disc / Q000502:physiology* / Q000601:surgery*; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology / Q000601:surgery; D008159:Lumbar Vertebrae; D010084:Oxidation-Reduction; D019736:Prostheses and Implants; D016059:Range of Motion, Articular / Q000502:physiology*; D015203:Reproducibility of Results; D012756:Sheep; D059145:Total Disc Replacement / Q000379:methods
chemical_list: D005780:Gelatin; D006820:Hyaluronic Acid