title: Proximal junctional kyphosis in adult reconstructive spine surgery results from incomplete restoration of the lumbar lordosis relative to the magnitude of the thoracic kyphosis.
abstract: BACKGROUND
  PROXIMAL JUNCTIONAL KYPHOSIS (PJK) IS DEFINED AS: 1) Proximal junction sagittal Cobb angle >≥10°, and 2) Proximal junction sagittal Cobb angle of at least 10° greater than the pre-operative measurement PJK is a common complication which develops in 39% of adults following surgery for spinal deformity. The pathogenesis, risk factors and prevention of this complication are unclear.
  
  
  METHODS
  Of 54 consecutive adults treated with spinal deformity surgery (age≥59.3±10.1 years), 19 of 54 (35%) developed PJK. The average follow-up was 26.8 months (range 12 - 42). Radiographic parameters were measured at the pre-operative, early postoperative (4-6 weeks), and final follow-up visits. Sagittal alignment was measured by the ratio between the C7-plumbline and the sacral-femoral distance. Binary logistic regression model with predictor variables included: Age, BMI, C7-plumbline, and whether lumbar lordosis, thoracic kyphosis and sacral slope were present
  
  
  RESULTS
  Patients who developed PJK and those without PJK presented with comparable age, BMI, pelvic incidence and sagittal imbalance before surgery. They also presented with comparable sacral slope and lumbar lordosis. The average magnitude of thoracic kyphosis was significantly larger than the lumbar lordosis in the proximal junctional kyphosis group, both at baseline and in the early postoperative period, as represented by [(-lumbar )lordosis - (thoracic kyphosis)]; no- PJK versus PJK; 6.6°±23.2° versus -6.6°±14.2°; p≥0.012. This was not effectively addressed with surgery in the PJK group [(-LL-TK): 6.2°±13.1° vs. -5.2°±9.6°; p≥0.004]. This group also presented with signs of pelvic retroversion with a sacral slope of 29.3°±8.2° pre-operatively that was unchanged after surgery (30.4°±8.5° postoperatively). Logistic regression determined that the magnitude of thoracic kyphosis and sagittal balance (C7-plumbline) was the most important predictor of proximal junctional kyphosis.
  
  
  CONCLUSIONS
  Proximal junctional kyphosis developed in those patients where the thoracic kyphosis remained greater in magnitude relative to the lumbar lordosis, and where the sagittal balance seemed corrected, but part of thise correction was secondary to pelvic retroversion.
  
  
  METHODS
  Prognostic case-control study - Level III.
authors.affiliation: Department of Orthopaedic Surgery The University of Iowa, Iowa City, USA.
authors.forename: Sergio
authors.initials: S
authors.lastname: Mendoza-Lattes
authors.forename: Zachary
authors.initials: Z
authors.lastname: Ries
authors.forename: Yubo
authors.initials: Y
authors.lastname: Gao
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Weinstein
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000453:epidemiology*; D008141:Lordosis / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009985:Orthopedics / Q000379:methods / Q000706:statistics & numerical data; D011183:Postoperative Complications / Q000453:epidemiology*; D015995:Prevalence; D011379:Prognosis; D011859:Radiography; D019651:Plastic Surgery Procedures / Q000009:adverse effects / Q000379:methods / Q000706:statistics & numerical data; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery
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