title: A posterior tether for fusionless modulation of sagittal plane growth in a sheep model.
abstract: METHODS
  This was an in vivo and in vitro investigation of a minimally invasive posterior tether system for fusionless modulation of sagittal plane growth in an immature sheep model.
  
  
  OBJECTIVE
  To determine whether fusionless modulation of spinal growth in the sagittal plane of an immature sheep model can be successfully performed.
  
  
  BACKGROUND
  Scheuermann's disease has been reported to affect 1% to 8% of the pediatric population. Varying degrees of spinal bone growth modulation has been successfully performed in the coronal plane of animal models. This represents the first attempt to modulate spinal growth in the sagittal plane in an animal model. Modulation of spinal growth in the sagittal plane may play a role in the treatment of pediatric kyphosis when brace treatment is unsuccessful.
  
  
  METHODS
  There were nine immature sheep posteriorly tethered and five control animals, all with identical follow-ups. Pedicle screws were placed in adjacent vertebrae, bilaterally, at the thoracolumbar junction and the lower lumbar spine. Polyethylene cords were passed subcutaneously, and tensioned to 20 lbs. Tethers were released in four sheep at 6 months and four at 12 months. At 12 months and 2 weeks, all animals were sacrificed.
  
  
  RESULTS
  At 13 months after surgery, the tethered groups had significantly less kyphosis and vertebral body wedging than the control group. In both the tethered groups, at 13 months after surgery, there was significantly less vertebral body wedging compared with the preoperative values. There was no evidence of facet arthropathy, but heterotopic ossification was seen in several specimens. Tethered spines had significantly less motion than control spines. Histologic evaluation demonstrated no detrimental results.
  
  
  CONCLUSIONS
  Fusionless modulation of sagittal plane growth in an immature sheep model was successfully performed with changes in the overall sagittal profile of the instrumented segments and vertebral body wedging. Increased stiffness of the instrumented segments posttether release was thought to be related to heterotopic ossification. Results suggest that this may be a potential treatment for adolescents with Scheuermann's disease.
authors.affiliation: Woodridge Spine Center, Wheat Ridge, CO 80033, USA. woodridgespine@aol.com
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Lowe
authors.forename: Lucas
authors.initials: L
authors.lastname: Wilson
authors.forename: Jui-Teng
authors.initials: JT
authors.lastname: Chien
authors.forename: Breton G
authors.initials: BG
authors.lastname: Line
authors.forename: Lisa
authors.initials: L
authors.lastname: Klopp
authors.forename: Donna
authors.initials: D
authors.lastname: Wheeler
authors.forename: Fred
authors.initials: F
authors.lastname: Molz
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000379:methods; D001861:Bone Regeneration; D001863:Bone Screws; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000502:physiology; D007738:Kyphosis / Q000628:therapy*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000254:growth & development* / Q000502:physiology; D023421:Models, Animal; D011859:Radiography; D012756:Sheep; D017792:Surgical Stapling / Q000379:methods*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000254:growth & development* / Q000502:physiology