Authors: Peter Gust Passias; Samantha Horn; Tina Raman; Virginie Lafage; Cole Bortz; Frank Segreto; Pawel Jankowski; Frank Schwab; Christopher Shaffrey; Christopher Shaffrey; International Spine Study Group (Brooklyn Heights, NY)

Introduction: Correction of cervical deformity(CD) often involves different types of osteotomies to address sagittal malalignment. Few studies have investigated the effect of osteotomy grade/location on regional and global alignment outcomes. Methods: CD was defined:C2-C7 Cobb>10°, CL>10°, cSVA>4cm, or CBVA>25°. Patients were evaluated for level and type of cervical osteotomy. Osteotomy grading used Ames-ISSG Osteotomy Classification:partial facet resection(grade 1), complete facet resection/ponte(2), partial/complete corpectomy(3), uncovertebral joint resection(4), opening wedge(5), closing wedge(6), vertebral column resection(7). Results: Included: 86 CD patients(61.4±10.6yrs, 66.3%F). A total of 141 osteotomies were performed in the cervical spine; the most common levels were C6(26.2%), C5(24.1%), C7(23.4%), and C4(20.6%). 79 osteotomies were in the thoracic spine; 75% were above T5(commonly T1,T2). 18 major osteotomies were performed(grades 6-7); 50% at T1. Cervical osteotomy patients improved in TS-CL, CL, C2 slope and worsened in T1 slope(25° to 33°,p<0.001) and SVA(9mm to 28mm,p=0.03). Upper thoracic osteotomy patients improved in TS-CL, cSVA, C2-T3, C2-T3 SVA and C2 slope(all p<0.05). Lower-thoracic osteotomy patients didn't significantly improve in cervical or global alignment from pre- to post-op, but did trend towards improvement in TS-CL, cSVA, SVA. Minor osteotomies in the upper thoracic spine showed improvement in cSVA(63mm to 49mm,p=0.022), C2-T3(p=0.007), and SVA(-16mm to 27mm,p<0.001). The greatest amount of C2-T3 angular change occurred for patients with major osteotomy at T2(39.1° change), T3(15.7°), C7(16.9°) and T1(13.5°). Upper thoracic major osteotomy patients showed similar pre- to post-operative radiographic changes as patients with 3+ minor osteotomies, though C2-T3 SVA trended towards greater improvement with a major osteotomy(-22.5mm vs +5.9mm,p=0.058) due to lever arm effect. Conclusion: CD patients undergoing cervical and upper thoracic osteotomies showed improvement in TS-CL, C2 slope. In the upper thoracic spine, multiple minor osteotomies or major osteotomy at a single level achieved similar alignment changes. Major osteotomy at T2 had the greatest overall impact in cervicothoracic/global alignment.