title: Incidence, risk factors and classification of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis.
abstract: METHODS
  Retrospective case series of surgically treated adult scoliosis patients.
  
  
  OBJECTIVE
  To assess the incidence, risk factors and clinical outcomes of proximal junctional kyphosis (PJK) in a large series of adult idiopathic scoliosis patients undergoing long instrumented spinal fusion (.5 vertebrae). A new classification is also projected.
  
  
  BACKGROUND
  Maintaining both coronal and sagittal balance is essential in the surgical treatment of adult deformity patients. PJK is a well-recognized postoperative phenomenon in adults and adolescents after scoliosis surgery. Despite recent reports, the prevalence, clinical outcomes, and the risk factors of PJK are still controversial.
  
  
  METHODS
  This study is a retrospective review of the charts and radiographs of 157 consecutive patients with adult scoliosis treated with long instrumented spinal fusion. PJK was defined by a proximal junctional angle greater than 108 and at least 108 greater than the corresponding preoperative measurement. Radiographic measurements included sagittal vertical axis (SVA), thoracic kyphosis (TK), lumbar lordosis (LL) and pelvic incidence (PI) on preoperative, immediate postoperative and at follow-up. Bone mineral density (BMD), Body mass index (BMI), age, sex, instrumentation type, surgery type, and fusion to sacrum were reviewed. Postoperative SRS outcome scores and Oswestry Disability Index (ODI) were also evaluated. PJK was graded by the severity and type. Means were compared with Student's t test and χ2 test. P value of less than 0.05 with confidence interval 95% was considered significant.
  
  
  RESULTS
  The average age was 46.9 years (22-81 years) and the average Follow-up was 4.3 years (2-12 years). PJK occurred in 32 patients (20%) and were mostly classified as 1A (Ligamentous & mild) deformity. The SRS outcome scores and ODI did not demonstrate significant differences between PJK group and non-PJK group, four patients had additional surgeries performed for local pain. Fusion to the sacrum and posterior fusion with segmental instrumentation were significant risk for PJK (P = 0.03, P < 0.01). BMD, BMI, age, sex, and instrumentation type showed no difference. Eighty-four percent of PJK group was associated with TK 1 LL 1 PI .458 or preoperation to postoperation SVA more than 50 mm vs. 6.4% of non-PJK group (P < 0.01, P < 0.01).
  
  
  CONCLUSIONS
  Despite the occurrence of PJK in 20% of adult scoliosis patients undergoing long fusion, no significant differences were found in SRS outcome scores and ODI in PJK and non-PJK patients. Fusion to the sacrum and posterior fusion with segmental instrumentation were identified as risk factors. PJK can be minimized by post-operative normalization of global sagittal alignment. A simplified classification based in severity type of PJK showed the majority in class 1A (ligamentous lesion and mild deformity).
authors.affiliation: Hospital for Special Surgery and National Hospital Organization, Murayama Medical Center, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Yagi
authors.forename: King B
authors.initials: KB
authors.lastname: Akilah
authors.forename: Oheneba
authors.initials: O
authors.lastname: Boachie-Adjei
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan; D007738:Kyphosis / Q000145:classification / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology* / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000601:surgery*; D012720:Severity of Illness Index; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation; D011795:Surveys and Questionnaires; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult