Reproducibility Measuring the Angle of Proximal Junctional Kyphosis Using the First or the Second Vertebra Above the Upper Instrumented Vertebrae in Patients Surgically Treated for Scoliosis

Study Design. A historical cohort study. Objective. To evaluate the reproducibility of this measure in proximal junctional kyphosis (PJK) and to determine whether differences exist between first and second vertebrae angles. Summary of Background Data. There are no previous studies on the precision and accuracy of selecting the first or the second vertebra above the upper instrumented vertebrae to determine the degree of spinal angulation after surgery. In several studies, the first or the second vertebrae above the upper instrumented vertebrae (UIV) have been selected to measure the angle of PJK in a surgical setting. However, to our knowledge, no studies have addressed the reliability of this measure. We aimed to evaluate the reproducibility of this measure in PJK and to determine whether differences exist between first and second vertebrae angles. Methods. A total of 38 randomly ordered radiologic digital images were obtained at 2 different times from 19 consecutive patients (aged 18.4 ± 6.0 years at intervention) surgically treated for scoliosis. Using these images in a blinded manner, 2 surgeons independently measured angles at both the first and second vertebrae above the UIV. The measures were repeated in different periods to test intra- and intersurgeon concordances. Results. For 152 measures, intrasurgeon concordance correlation coefficients ranged from 0.78 to 0.92 (high to very high reproducibility) and comparative intersurgeon concordance correlation coefficients ranged from 0.55 to 0.80 (moderate to high reproducibility). No differences were found between the first and the second vertebrae angles. Conclusion. Good reproducibility and agreement using the first and second vertebrae above the UIV to measure the angle of PJK was found in this study.