Relationship between postoperative pelvic rotation and osteotomy site and angle in thoracolumbar kyphosis of ankylosing spondylitis

English Keywords:Ankylosing spondylitis  Thoracolumbar kyphosis  Pelvic rotation  Osteotomy site  Osteotomy angle

English Abstract:

  【Abstract】 Objectives: To explore the relationship between pelvic rotation, osteotomy site and osteotomy angle in patients with thoracolumbar kyphosis of ankylosing spondylitis(AS). Methods: 13 AS patients with thoracolumbar kyphosis, who underwent double-level pedicle subtraction osteotomy(PSO) between August 2017 and April 2021, were retrospectively analyzed. There were 11 males and 2 females, aged 43.5±8.5 years(29-58 years). A total of 26 PSO osteotomy were performed. The osteotomy angle was 35.6°±9.0°, the operative time was 434.2±117.1min, and the intraoperative blood loss was 2480.5±1486.3mL. The follow-up time was 29.0±4.0months(24-38months). The global kyphosis(GK), thoracic kyphosis(TK), lumbar lordosis(LL), sagittal vertical axis(SVA), horizontal distance between hip axis and hilus pulmonis(HDHH), pelvic tilt(PT), sacral slope(SS), and pelvic incidence(PI) were measured on the preoperative, two weeks postoperative, and final follow-up full-length lateral radiographs of the spine. The changes in PT(ΔPT) at two weeks after operation and final follow-up from the preoperative PT value were recorded, namely, postoperative pelvic rotation angle, which were recorded as two weeks-postoperative ΔPT and final follow-up ΔPT, respectively. The osteotomy angle was measured and recorded on the thoracolumbar CT two weeks after operation. The distances and angles between hip axis(HA), hilus pulmonis(HP) and the osteotomy apex were measured in the plane coordinate axis with the hip axis as the origin established on the preoperative full-length lateral spine X-ray film. The coordinate of the apex and the distances to and angles with HA and HP were used to represent the osteotomy site. The functional relationship between the pelvic rotation angle and the osteotomy site and osteotomy angle was calculated, and the ΔPT value calculated by the formula was obtained. Paired t test was used to verify the accuracy of the formula by comparing the ΔPT calculated by the formula with the ΔPT of 2 weeks after operation and the ΔPT of the final follow-up. Results: The GK, LL, SVA, HDHH, SS, and PT were 94.8°±15.1°,-17.0°±24.9°, 29.4±6.9cm, 10.3±8.8cm, 5.7°±10.3°, and 43.6°±14.5°, respectively before operation, which were 34.0°±18.5°, 34.1°±15.1°, 10.4±4.5cm, 1.7±4.7cm, 24.6°±7.1°, and 24.5°±8.3° two weeks after operation, and 34.2°±18.0°、36.9°±19.4°、9.8±4.0cm、1.2±3.3cm、24.8°±7.3°, and 25.1°±7.8° at final follow-up. The above indexes two weeks after operation were significantly different from those before operation(P<0.05). The TK and PI were 51.6°±19.4° and 49.3°±10.5° before operation, and 45.8°±18.7° and 48.8°±12.0° two weeks after surgery, with no significant difference(P>0.05). There was no significant difference in GK, TK, LL, SVA, HDHH, PI, SS, and PT between two weeks after operation and final follow-up(P>0.05). The formula-calculated ΔPT, two-weeks postoperative ΔPT, and final follow-up ΔPT were 17.8°±8.9°, 19.2°±8.6°, and 18.5°±8.4°, respectively, with no significant statistical differences between(P>0.05). Conclusions: There is an function relationship between the pelvic rotation after osteotomy in AS patients with thoracolumbar kyphosis and the site and angle of osteotomy.