title: Biomechanical study of the spinal cord in thoracic ossification of the posterior longitudinal ligament.
abstract: BACKGROUND
  Ossification of the posterior longitudinal ligament (OPLL) in the thoracic spine produces myelopathy. This is often progressive and is not affected by conservative treatment. Therefore, decompressive surgery is usually chosen.
  
  
  OBJECTIVE
  To conduct  a stress analysis of the thoracic OPLL.
  
  
  METHODS
  The three-dimensional finite element spinal cord model was established. We used local ossification angle (LOA) for the degree of compression of spinal cord. LOA was the medial angle at the intersection between a line from  the superior posterior margin at the cranial vertebral body of maximum OPLL to the top of OPLL with beak type, and a line from the lower posterior margin at the caudal vertebral body of the maximum OPLL to the top of OPLL with beak type. LOA 20°, LOA 25°, and LOA 30° compression  was applied to the spinal cord in a preoperative model, the posterior decompressive model, and a model for the development of kyphosis.
  
  
  RESULTS
  In a preoperative model, at more than LOA 20° compression, high stress distributions in the spinal cord were observed. In  a posterior decompressive model, the stresses were lower than in the preoperative model. In the model for development of kyphosis, high-stress distributions were observed in the spinal cord at more than LOA 20° compression.
  
  
  CONCLUSIONS
  Posterior decompression was an  effective operative method. However, when the preoperative LOA is more than 20°, it is very likely that symptoms will worsen. If operation is performed at greater than LOA 20°, then correction of kyphosis by fixation of instruments or by forward decompression should be considered.
authors: Yamaguchi University Graduate School of Medicine, Ube, Yamaguchi, Japan. n005uk@yamaguchi-u.ac.jp
authors: Norihiro
authors: N
authors: Nishida
authors: Yoshihiko
authors: Y
authors: Kato
authors: Yasuaki
authors: Y
authors: Imajo
authors: Syunichi
authors: S
authors: Kawano
authors: Toshihiko
authors: T
authors: Taguchi
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D019299:Decompression, Surgical / Q000379:methods; D006801:Humans; D007738:Kyphosis / Q000601:surgery; D008954:Models, Biological; D017887:Ossification of Posterior Longitudinal Ligament / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery; D013904:Thoracic Vertebrae / Q000503:physiopathology* / Q000601:surgery