Criteria for Severe Dynamic Sagittal Imbalance in Adult Spinal Deformity and its Importance

Abstract

Abstract Background To analyze the characteristics of “severe” dynamic sagittal imbalance (DSI) in patients with adult spinal deformity (ASD) and establish criteria for them. Methods In total, 102 ASD patients with four cardinal signs of lumbar degenerative kyphosis were retrospectively analyzed. All patients underwent deformity corrective surgery and were divided into three groups according to the diagnostic criteria. The criteria were based on the Oswestry disability index scores and dynamic features (△Timewalk: time until C7 sagittal vertical axis [C7SVA] reaches ≥ 20 cm after the start of walking) of sagittal imbalance. The paravertebral back muscles were analyzed and compared using T2-weighted axial images. We performed a statistically time-dependent spinopelvic sagittal parameter analysis on full standing lateral lumbar radiographs. Lumbar flexibility was analyzed based on dynamic lateral lumbar radiographs Results Based on the diagnostic criteria, the 102 patients were classified into three groups: mild (△Timewalk ≥ 180 s, 35 patients), moderate (180 s > △Timewalk ≥ 30 s, 38 patients), and severe (△Timewalk < 30 s, 29 patients). There was a significantly higher signal intensity (533.4 ± 237.5, P < 0.05) and larger area of fat infiltration (35.2 ± 5.4, P < 0.05) in the back muscles of the severe group than in the mild (223.8 ± 67.6/22.9 ± 11.9) and moderate groups (294.4 ± 214.7/21.6 ± 10.6). The analysis of lumbar flexibility revealed significantly lower values in the severe group (5.8° ± 2.5°, P < 0.05) than in the mild and moderate groups (14.2° ± 12.4° and 11.4° ± 8.7°, respectively). The severe group had significantly lower lumbar lordosis (LL, 25.1° ± 22.7°, P < 0.05) and Pelvic incidence (PI)-LL mismatch (PI-LL, 81.5° ± 26.6°, P < 0.001) than the mild (8.2 ° ± 16.3°/58.7° ± 18.8°) and moderate (14.3° ± 28.6°/66.8° ± 13.4°) groups. In ROC curve analysis, PI-LL was statistically significant with AUC of 0.810 (95% confidence interval) when the baseline was set at 75.3°. The severe group showed more postoperative complications than the other groups. Conclusions We suggest the following criteria for severe DSI: C7SVA > 20 cm within 30 s after walking or standing, rigid lumbar curve < 10° on dynamic lateral radiographs, and PI-LL mismatch > 75.3°.