Proximal Junctional Kyphosis: Inter- and Intra-observer Reliability of Radiographic Measurements in Adult Spinal Deformity.

STUDY DESIGN: Reliability study of radiographic measures of proximal junctional kyphosis in adult spinal deformity patients. OBJECTIVE: Assess impacts of level of proximal endpoint and vertebral fracture on reliability of measurement of junctional kyphosis. SUMMARY OF BACKGROUND DATA: Radiographic assessment is important in determining management of patients with Proximal Junctional Kyphosis (PJK) or Proximal Junctional Failure (PJF). No study to date has evaluated the reliability of radiographic measurement of the junctional kyphotic angle after surgery for Adult Spinal Deformity (ASD). METHODS: Post-operative radiographs from 52 ASD patients were divided into four categories based on the level of the upper instrumented vertebra (UIV) and the presence or absence of PJF: upper thoracic without failure (UT), thoracolumbar without failure (TL), upper thoracic with PJF (UTF) and thoracolumbar with PJF (TLF). Nine surgeon reviewers performed radiographic measurements of kyphosis between UIV+2 and UIV twice at least 4-weeks apart. Intraclass correlation coefficients (ICC) were calculated to determine inter- and intra-observer reliability. RESULTS: Inter-observer reliability for measurements of UT, TL, UTF, TLF were all almost perfect with ICC scores of 0.917, 0.965, 0.956, 0.882, and 0.932, 0.975, 0958, 0.989, for sessions 1 and 2 respectively. Similarly, ICC\u27s for kyphosis measurements for the TL and TLF group had almost perfect agreement with means of 0.898 (range: 0.817-0.969) and 0.976 (range: 0.931-0.995), respectively. ICC\u27s for measurements for the UT and UTF groups all had substantial or almost perfect agreement with means of 0.801 (range: 0.662-0.942) and 0.879 (range: 0.760-0.988), respectively. CONCLUSION: This study demonstrates high inter- and intra-observer reliability of proximal junctional kyphosis measurement following instrumented fusion for ASD, independent of the presence or absence of PJF. Although slightly lower for upper thoracic than for thoracolumbar proximal endpoints, all ICC\u27s consistently reached at least substantial agreement and near perfect agreement for most. LEVEL OF EVIDENCE: 4