Fig. 1

The pre-and postoperative radiographs of a 15-year-old female patient with low PI (PI = 28°) who developed PJK after surgery. She underwent T6-L3 instrumentation. The thoracolumbar junction is corrected from kyphosis to lordosis. Postoperative TK was significantly reduced, while the PJA was significantly increased and PJK occurred at 2 years’ follow-up. Other sagittal parameters did not change significantly (a to c). In the coronal plane, the major thoracolumbar curve was corrected from 48.2° to 3.3°, which remained stable (3.7°) at a two-year follow-up. The UIV was T6 and the LIV was L3 (d to f). The apex of thoracic kyphosis was T7 (a). PI, pelvic incidence; SS, sacral slope; LL, lumbar lordosis; TK, thoracic kyphosis; GTK, global thoracic kyphosis; PJA, proximal junctional angle; TLK, thoracolumbar junctional kyphosis angle; SVA, sagittal vertical axis