Disparities in Presentation and Outcomes of Symptomatic Proximal Junctional Kyphosis Based on Over and Under Correction in Adult Spinal Deformity Corrections: A Multicenter Analysis

Introduction: Age-adjusted alignment goals were devised to mitigate overcorrection in older ASD patients. To date, the assessment of over and under-correction in age-adjusted targets and factors determinant of PJK and PJK requiring reoperation remains to be elucidated.

Methods: ASD patients fused from at least L1 and proximal to sacrum with 2Y data were included. Radiographic PJK(radPJK) was defined by Lafage et al. criteria: >22° change from baseline in PJA & PJA >28°. RadPJK and reoperation for PJK(reopPJK) were evaluated by summation of the SAAS components(TPA, PT, PI-LL). SAAS score was matched(M) if between -1 and 1, under(U) if <-1, and overcorrected(O) if >1. Score was adjusted by one point for each 20-year deviation from target. Greater SAAS mismatch was evaluated by 1 and 2 standard deviations(SD) from the mean postoperative SAAS score.

Results: 1065 patients met inclusion. O had earlier onset of radPJK and reopPJK relative to those U(p <.05). Multivariable analysis depicted increased O to have a progressively higher likelihood of radPJK, with O having 1.8x higher odds of radPJK and 5x higher odds of reopPJK compared to U(all p<.05). Increasing age and frailty in O were significant factors increasing the likelihood of reopPJK, whereas lower PI was for U. SAAS score of >2(0.3 SD) and >5(1.1 SD) increased the likelihood of radPJK and reopPJK respectively, while U to <-6 was for reopPJK. In those requiring reopPJK, U had worse ODI, SRS22r pain, appearance, and satisfaction at the time of occurrence(p <.05). Reoperation improved HRQLs, however to a lesser extent for those mismatched in SAAS. U had a lower MCID rate at 2Y for ODI, SRS22r activity, pain, appearance, and satisfaction(p <.05). PJK prophylaxis affected HRQLs to a greater extent in O relative to U, with 1.5x higher rate of reaching MCID(p <.05).

Conclusion : Under-correction required greater malalignment based on age-adjusted targets, than overcorrection for the development of symptomatic PJK. Those overcorrected were more likely to have earlier and more severe PJK requiring reoperation, while those under-corrected presented with worse disability.