Fig. 2

A 49-year old male patient with AS. a The preoperative X-ray showed that the parietal vertebrae were located at L2, which belonged to the lumbar lordosis group. b Single-segment pedicle subtraction osteotomy (PSO) was conducted at L1. Lumbar lordosis, global kyphosis, and sagittal vertical axis improved from the preoperative –25°, 79°, and 104.21 mm to –53°, 61°, and 30.34 mm, respectively. c At the last follow-up in the 30th-month post-operation, no apparent orthopedic loss was observed, and lumbar lordosis, global kyphosis, and sagittal vertical axis were –49°, 51°, and 31.76 mm, respectively