Abstract
BACKGROUND: Sagittal spinopelvic parameters remain poorly defined in patients with Scheuermann disease (SD). For example, although pelvic incidence (PI) should approximate lumbar lordosis (LL) by 10°, this is not true in patients with SD. This retrospective radiographic study was conducted to propose a new mathematical relationship between sagittal spinopelvic parameters in skeletally mature patients with SD. METHODS: The following formula (Δ) was proposed [(thoracic kyphosis - 45°) + (thoracolumbar kyphosis - 0°) + (PI - LL) = ± 10°] and validated with standard spino pelvic parameters in patients with skeletally mature SD without prior spine surgery at 2 centers between 2006 and 2015. The T1 pelvic angle (TPA) was used as a measure of global balance with normal maximum of 15°. Subgroup analysis was performed to compare Δ between balanced (TPA ≤ 15°) and unbalanced (TPA > 15°) patients with SD. RESULTS: In patients with SD (n = 30), half were female (n = 15), the average age was 39 years, and the average Δ was 2.4°. A significant correlation was discovered between Δ and both TPA (R (2) = 0.75) and PI (R (2) = 0.69). At TPA of 15°, average Δ was 9.2°. There was also a significant difference between balanced and unbalanced patients (-8.7° ± 11.6° versus 28.2° ± 19.7°, P = .0003). CONCLUSIONS: This study of a new formula (Δ) to evaluate global sagittal balance in patients with SD found that accounting for the kyphosis maintained Δ within ± 10°. Further study is planned to determine whether maintaining and/or restoring a normal Δ is associated with improved outcomes in patients with SD after surgery.