Should the C7-T1 Junction Be Feared? The Effect of a T1 Upper Instrumented Vertebra on Development of Proximal Junctional Kyphosis

Purpose: Proximal junctional kyphosis is an infrequent complication in AIS; however, equipoise remains on the effects of ending a fusion proximally at the C7-T1 junction on the future development of PJK. The purpose of this study was to determine the rate of PJK in patients with AIS who had a UIV of T1 vs those with a UIV of T2 at 5 years of follow-up. Methods: A query was performed of a prospective, multi-center AIS database of patients who received a PSF with at least 5 years of follow-up. Patients with a T1 UIV (n = 29) were compared to those with a T2 UIV (n = 58). PJK was defined as a proximal junctional angle (PJA) > 10 degrees. Results: There was no difference between the T1 and T2 UIV cohorts in preoperative T2-T12 kyphosis or pelvic incidence; however preoperatively, T1 UIV patients had a significantly decreased PJA at − 3° ± 4.5° as compared to T2 UIV patients 1.6° ± 6.5° (p = 0.0014). No patients with a T1 UIV experienced PJK at 5-years of follow-up, while 16% of patients with a T2 UIV experienced PJK (p = 0.025). No patients in the T2 UIV cohort required revision surgeries for their PJK. There was no difference found in total SRS22 scores, however at 5 years of follow-up, T2 UIV patients had better Pain domain scores (4.4 ± 0.6) vs T1 UIV patients (4.0 ± 0.6; p = 0.004). Conclusion: While T1 is an uncommon UIV in AIS, at 5 years of follow-up, a T1 UIV did not result in PJK, nor did it result in a clinically significant change in patient-reported outcome scores.