- Evidence of severe cervical spinal deformity based on Ames classification: C2-C7 SVA > 8cm, Horizontal Gaze < -10 or > 25, T1S-CL > 20, myelopathy (JOA score <10) or severe adult spinal deformity based on SRS-Schwab classification (PI-LL > 20, PT >30, SVA > 90 mm)