title: A systematic review of definitions and classification systems of adjacent segment pathology.
abstract: METHODS
  Systematic review.
  
  
  OBJECTIVE
  To undertake a systematic review to determine how "adjacent segment degeneration," "adjacent segment disease," or clinical pathological processes that serve as surrogates for adjacent segment pathology are classified and defined in the peer-reviewed literature.
  
  
  BACKGROUND
  Adjacent segment degeneration and adjacent segment disease are terms referring to degenerative changes known to occur after reconstructive spine surgery, most commonly at an immediately adjacent functional spinal unit. These can include disc degeneration, instability, spinal stenosis, facet degeneration, and deformity. The true incidence and clinical impact of degenerative changes at the adjacent segment is unclear because there is lack of a universally accepted classification system that rigorously addresses clinical and radiological issues.
  
  
  METHODS
  A systematic review of the English language literature was undertaken and articles were classified using the Grades of Recommendation Assessment, Development, and Evaluation criteria. RESULTS.: Seven classification systems of spinal degeneration, including degeneration at the adjacent segment, were identified. None have been evaluated for reliability or validity specific to patients with degeneration at the adjacent segment. The ways in which terms related to adjacent segment "degeneration" or "disease" are defined in the peer-reviewed literature are highly variable.
  
  
  CONCLUSIONS
  On the basis of the systematic review presented in this article, no formal classification system for either cervical or thoracolumbar adjacent segment disorders currently exists.
  
  
  METHODS
  No recommendations regarding the use of current classification of degeneration at any segments can be made based on the available literature. A new comprehensive definition for adjacent segment pathology (ASP, the now preferred terminology) has been proposed in this Focus Issue, which reflects the diverse pathology observed at functional spinal units adjacent to previous spinal reconstruction and balances detailed stratification with clinical utility. A comprehensive classification system is being developed through expert opinion and will require validation as well as peer review. Strength of Statement: Strong.
authors.affiliation: Indiana Spine Group, Department of Orthopaedic Surgery, Indiana University, Carmel, IN 46032, USA. pkraemer@indianaspinegroup.com
authors.forename: Paul
authors.initials: P
authors.lastname: Kraemer
authors.forename: Michael G
authors.initials: MG
authors.lastname: Fehlings
authors.forename: Robin
authors.initials: R
authors.lastname: Hashimoto
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lee
authors.forename: Paul A
authors.initials: PA
authors.lastname: Anderson
authors.forename: Jens R
authors.initials: JR
authors.lastname: Chapman
authors.forename: Annie
authors.initials: A
authors.lastname: Raich
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Norvell
mesh_terms: D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000175:diagnosis* / Q000473:pathology*; D019651:Plastic Surgery Procedures / Q000379:methods; D012720:Severity of Illness Index; D013123:Spinal Fusion / Q000379:methods; D013131:Spine / Q000473:pathology* / Q000601:surgery