A Single Sagittal Parameter for Decision Making in Adult Spinal Deformity

Objective: Decision-making in adult spinal deformity (ASD) remains challenging with complex algorithms and scores inhibiting every day use. Thus, there is an appetite for a simplified parameter to be identified that can guide surgical decision-making. This study therefore questions whether a simplified sagittal modifier (SSM) or relative spinopelvic alignment (RSA) could offer a reliable tool to determine operative intervention in patients with ASD. Methods: Multicenter, prospective study of consecutive ASD patients. Inclusion criteria were ASD patients presenting with at least one criteria: Cobb ≥ 20°; SVA ≥ 5 cm; TK ≥ 60° or PT ≥ 25°. A total of 1238 patients (431 non-operative and 807 operative) were classified according to their SSM and RSA. A Chi2 test was performed for surgical indication (operated or not). p<0.05 value was considered significant. Results: For non-operative patients: 235 (55%) were classified as aligned with SSM and 323 (75%) with the RSA; 157 (36%) vs. 39 (9%) respectively as moderate and 39 (9%) vs. 69 (16%) respectively as severe malalignment. For operative patients: 252 (31%) vs. 388 (48%) respectively were classified as aligned, 289 (36%) vs. 96 (12%) respectively as moderate and 266 (33%) vs. 323 (40%) respectively as severe malalignment with each respective modifier. Both modifiers were significant (p<0.01) for decision-making. Conclusions: Both the SSM and RSA are significantly correlated to the intention to surgically treat patients with ASD. RSA is a simple and powerful parameter that is more discriminant than SSM in decision-making. RSA should be considered as a parameter that can guide the decision for surgical intervention in patients with ASD.