Selection of distal fusion level in posterior instrumentation and fusion of Scheuermann kyphosis: is fusion to sagittal stable vertebra necessary?

PURPOSE: Distal junctional kyphosis (DJK) is a major instrumentation-related complication after the surgical correction of Scheuermann kyphosis (SK). The exact criteria to avoid DJK have been controversial. It has been recommended to include the SSV into the fusion by some authors, while others suggest that fusion to FLV is sufficient. The purpose of this study was to investigate the occurrence of DJK in relation to distal fusion level selection in SK surgery by investigating the relationship between the sagittal stable vertebra (SSV), first lordotic vertebra (FLV), and the lowest instrumented vertebra (LIV). METHODS: 54 patients (mean age: 21.2 years, range 12-43; male/female: 20/34) with SK who were treated by posterior segmental instrumentation and fusion were prospectively evaluated. Patients were allocated into 3 groups according to distal fusion level. In group 1, SSV was chosen as LIV (n = 20), and in group 2, LIV was the FLV (n = 16). Third group consisted of 18 patients in whom SSV and FLV was the same vertebra. Distal junctional angle, sagittal plane analysis, and clinical outcomes according to SF-36 were evaluated. RESULTS: Mean preoperative kyphosis angles were 77.2°, 73.4°, and 76.7° in groups 1, 2, and 3, respectively (p = 0.281), which decreased to 38.1°, 37.3°, and 37.8° postoperatively at final follow-up (p = 0.988). Mean follow-up time was 28.3 months. Correction amounts were similar between the groups (p = 0.409). 3 patients in SSV group, 5 patients in FLV group, and 3 patients in SSV-FLV group developed DJK, which was statistically insignificant. The C7 sagittal plumbline, lumbar lordosis, and pelvic parameters were not significantly different before or after surgery between the groups. Preoperative and postoperative results of SF-36 questionnaire were similar in all the groups. None of the patients who had DJK required revision surgery during the follow-up time. CONCLUSION: Proper selection of distal fusion level is important in order to prevent DJK after SK surgery. According to this study, it is not necessary to extend the fusion down to the SSV. Fusion to FLV is sufficient and saves a level.