The Long-term Fate of Asymptomatic Proximal Junctional Kyphosis following Long Instrumented Fusion in Elderly Patients with Sagittal Imbalance.

STUDY DESIGN Retrospective study. OBJECTIVE To investigate the long-term fate of asymptomatic PJK focusing on the elderly patients with sagittal imbalance by comparing the patients with and without PJK. SUMMARY OF BACKGROUND DATA Most of previous studies demonstrated that PJK does not negatively affect the clinical outcome compared to that of the patients without PJK. The question "will the asymptomatic PJK remain asymptomatic even in long-term follow-up?" has not been answered yet because the previous results were based on the short follow-up duration. METHODS Patients > 60 years old who underwent ≥4-level fusions to the sacrum for sagittal imbalance were followed up for over five years. The radiographic and clinical outcomes were compared between PJK (n = 30) and non-PJK groups (n = 43). PJK was defined by proximal junctional angle (PJA) > 10°. Only patients with > 3 years of follow-up duration after PJK development were included in PJK group. The clinical outcome measures included visual analog scale (VAS) for the back and leg, Oswestry disability index (ODI), and Scoliosis Research Society (SRS)-22 scores. RESULTS The mean age was 69.2 years. Total follow-up duration was 92.4 months. Time between PJK development and the last follow-up was 67.4 months in PJK group. Although there were no differences between the two groups in terms of pelvic incidence-lumbar lordosis mismatch, pelvic tilt, or sacral vertical axis, PJA significantly increased from 6.5° postoperatively to 21.2° at the final follow-up in the PJK group. The clinical outcomes were worse (such as VAS for the back, ODI, and SRS-22 scores) in the PJK group than in non-PJK group, except for the satisfaction domain. Three (10%) of 30 patients underwent a revision surgery for PJK progression. CONCLUSIONS Even if PJK was asymptomatic at initial development, it progressed radiographically with time and eventually gave a negative impact on the clinical outcomes in long-term follow-up.Level of Evidence: 3.