1555. Effect of Age Adjusted Alignment Goals and Distal Inclination Angle on the Fate of Distal Junctional Kyphosis in Cervical Deformity Surgery

Authors: Peter Gust Passias; Samantha Horn, BA; Virginie Lafage, PhD; Renaud Lafage, MS; Justin Smith, MD; Breton Line, BS; Themistocles Protopsaltis, MD; Alex Soroceanu, MD; Cole Bortz, BA; Frank Segreto, BS; Haddy Alas, BS; Christopher Ames, MD (Brooklyn Heights, NY)

Introduction: DJK after CD surgery remains a challenge and outcomes are understudied. Methods: CD criteria: C2-C7 Cobb>10°, CL>10°, cSVA>4cm, CBVA>25°. DJK: angle<-10° from end of fusion construct to 2 nd distal vertebra, and change in this angle by<-10° from BL to post-op. Patients(pts) evaluated based on lower end of construct:Cervical(C7 or above), upper thoracic(UT:T1-T6), lower thoracic(LT:T7-T12). Age-adjusted alignment targets were calculated using published formulas for SVA, PI-LL, PT, TPA, LL-TK Results: 76 CD pts included(61.3yr,63%F). By 1Y, 20 pts developed DJK, with 4 requiring reoperation. The breakdown of LIV were:non-DJK pts had 27% cervical LIV, 68% UT, and 5% LT; DJK pts had 25% cervical, 50% UT, 25% LT. There were no differences in BL/1Y parameters for PI, PI-LL, SVA, TPA, PT parameters for actual and age-adjusted targets. DJK pts had worse BL cSVA(55mm v 41mm,p=0.027), more comorbidities and neurologic deficit, but similar frailty. At 1Y, DJK pts had more severe cSVA, C2-T3 SVA, and C2S(p<0.05). Offset between actual and ideal alignment for SVA, PT, TPA, PI-LL and LL-TK were similar between groups, though DJK trended towards larger SVA offset(-34mm v 8,p=0.09). There was no difference in LIV inclination angle between DJK and non-DJK. DJK pts with UT LIV had higher LIV-inclination angle+C2 tilt than non-DJK(61.9° v 41.1°,p=0.02), thus more anterior construct inclination. DJK pts with reop had significantly worse BL-1Y change in cervical parameters and trended towards larger age-adjusted global alignment offsets(SVA offset:reop -77mm v no reop -23mm,p=0.196) compared to non-reop DJK Conclusion: Age-adjusted alignment targets were unable to capture differences in these populations, suggesting the need for cervical-specific goals. DJK pts with upper thoracic LIV had a larger pt-specific LIV inclination angle and a more anterior construct inclination. Orientation of the distal-most instrumented level may have a role in its development, particularly when ending in the upper thoracic region