title: Proximal junctional kyphosis and failure after spinal deformity surgery: a systematic review of the literature as a background to classification development.
abstract: METHODS
  Systematic review of literature.
  
  
  OBJECTIVE
  To perform a comprehensive English language systematic literature review of proximal junctional kyphosis (PJK) and proximal junctional failure (PJF), concentrating on incidence, risk factors, health related quality of life impact, prevention strategy, and classification systems.
  
  
  BACKGROUND
  PJK and PJF are well described clinical pathologies and are a frequent cause of revision surgery. The development of a PJK classification that correlates with clinical outcomes and guides treatment decisions and possible prevention strategies would be of significant benefit to patients and surgeons.
  
  
  METHODS
  The phrases "proximal junctional," "proximal junctional kyphosis," and "proximal junctional failure" were used as search terms in PubMed for all years up to 2014 to identify all articles that included at least one of these terms.
  
  
  RESULTS
  Fifty-three articles were identified overall. Eighteen articles assessed for risk factors. Eight studies specifically reviewed prevention strategies. There were no randomized prospective studies. There were 3 published studies that have attempted to classify PJK. The reported incidence of PJK ranged widely, from 5% to 46% in patients undergoing spinal instrumentation and fusion for adult spinal deformity. It is reported that 66% of PJK occurs within 3 months and 80% within 18 months after surgery. The reported revision rates due to PJK range from 13% to 55%. Modifiable and nonmodifiable risk factors for PJK have been characterized.
  
  
  CONCLUSIONS
  PJK and PJF affect many patients after long segment instrumentation after the correction of adult spinal deformity. The epidemiology and risk factors for the disease are well defined. A PJK and PJF scoring system may help describe the severity of disease and guide the need for revision surgery. The development and prospective validation of a PJK classification system is important considering the prevalence of the problem and its clinical and economic impact.
  
  
  METHODS
  N/A.
authors.affiliation: *Department of Neurological Surgery, University of California, San Francisco †Department of Neurological Surgery, Northwestern University, Feinberg School of Medicine, Chicago, IL ‡University of Nevada, School of Medicine, Las Vegas, NV §Silicon Valley Spine Institute, Campbell, CA ¶Norwich Orthopedic Group, North Franklin, CT ∥Private Practice, Amarillo, TX **Bronson HealthCare Midwest Spine & Scoliosis Specialists, Kalamazoo, MI ††Instituto de Patologia da Coluna, Sao Paulo, Brazil ‡‡Otto-von-Guericke-Universität Magdeburg, Magdeburg, Germany §§College of Medicine, Kyung Hee University, Seoul, South Korea ¶¶Chirurgia del Rachide, Padova, Italy ∥∥Cedars Sinai Medical Center, Los Angeles, CA ***Royal North Shore Hospital, University of Sydney, Sydney, Australia †††Oregon Health and Science University, Portland, OR; and ‡‡‡Hey Clinic, Raleigh, NC.
authors.forename: Darryl
authors.initials: D
authors.lastname: Lau
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Clark
authors.forename: Justin K
authors.initials: JK
authors.lastname: Scheer
authors.forename: Michael D
authors.initials: MD
authors.lastname: Daubs
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Coe
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Paonessa
authors.forename: Michael O
authors.initials: MO
authors.lastname: LaGrone
authors.forename: Michael D
authors.initials: MD
authors.lastname: Kasten
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Amaral
authors.forename: Per D
authors.initials: PD
authors.lastname: Trobisch
authors.forename: Jung-Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Daniel
authors.initials: D
authors.lastname: Fabris-Monterumici
authors.forename: Neel
authors.initials: N
authors.lastname: Anand
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Cree
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hart
authors.forename: Lloyd A
authors.initials: LA
authors.lastname: Hey
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Ames
mesh_terms: D005260:Female; D006801:Humans; D007738:Kyphosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012600:Scoliosis / Q000503:physiopathology / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects / Q000191:economics / Q000295:instrumentation / Q000379:methods*; D013131:Spine / Q000601:surgery*; D016896:Treatment Outcome