What Is the More Appropriate Proximal Fusion Level for Adult Lumbar Degenerative Flat Back?

Abstract

To determine the optimal proximal fusion level after long instrumented fusion to the sacrum for lumbar degenerative flat back. Data from 70 patients with lumbar degenerative flat back were reviewed retrospectively. Three groups were designated according to the upper instrumented vertebrae (UIV): group 1 (UIV= T10 or above), group 2 (UIV= T11-12), and group 3 (UIV= L1 or below). Pre- and postoperative pelvic parameters, degree of correction, and prevalence of proximal junctional kyphosis (PJK) and its risk factors were evaluated. The prevalence of PJK was 27.1% (average 35.5 months of follow-up). Preoperative pelvic incidence (PI) and sacral slope (SS) in group 1 were higher in the PJK group than in the non-PJK group (P= 0.03 and P= 0.001, respectively). Preoperative thoracolumbar (TL) in group 3 was higher in the PJK group than in the non-PJK group (P= 0.01). Postoperative pelvic tilt (PT) was lower (<20°) in the non-PJK group than in the PJK group (P= 0.025 in group 3). Postoperative TL in group 3 was lower than in the non-PJK group (P= 0.024). If the PI is ≥50°, TL kyphosis is ≥5°, and SS is ≥20°, the UIV should be raised above T10 up to the midthoracic level. If the PI is ≥50°, SS is ≤20°, and thoracic kyphosis (TK) is normal despite TL kyphosis, the UIV should be at T10. Even if the PI is ≥50°, TK is normal, and there is no TL kyphosis, the UIV should be set at L1 or below. Regardless of the UIV, the postoperative PT should be ≤20°.