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

OBJECTIVE: To determine the optimal proximal fusion level after long instrumented fusion to the sacrum for lumbar degenerative flat back. METHODS: 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. RESULTS: 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 degrees) 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). CONCLUSIONS: If the PI is >= 50 degrees, TL kyphosis is >= 5 degrees, and SS is >= 20 degrees, the UIV should be raised above T10 up to the midthoracic level. If the PI is >= 50 degrees, SS is <= 20 degrees, and thoracic kyphosis (TK) is normal despite TL kyphosis, the UIV should be at T10. Even if the PI is >= 50 degrees, 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 degrees.