The association between locomotive function and incidence of proximal junctional kyphosis following adult spine deformity surgery.

Background And Objectives: This retrospective review study aimed to determine whether functional mobility test (FMT) results are related to the incidence of proximal junctional kyphosis (PJK) after surgical correction of adult spinal deformity (ASD).

Methods: A total of 157 patients who underwent reconstructive spinal surgery for ASD between July 2019 and December 2021 were included in this study. Three types of FMTs were performed preoperatively: timed-up-and-go (TUG) test, five times sit-to-stand (STS) test, and alternate step (AS) test. The primary outcome measure was the occurrence of PJK at 1 year after surgery. Oswestry disability index (ODI) and EuroQOL-5-dimension (EQ-5D) scores were surveyed as patient-reported outcome measures of the surgery.

Results: The occurrence of PJK was observed in 41 of the 157 patients (26.1%) at 1 year after surgery. Among the three functional mobility tests, STS test results were significantly higher in the patients who developed PJK. The receiver operating characteristics curve drawn with the STS test had an area under the curve of 0.69 and the optimal cutoff value was suggested as 22 seconds. Multivariate logistic regression analysis identified the STS test along with age and preoperative ODI score as the significant predictors of PJK (p = 0.026, 0.005 and 0.001, respectively).

Conclusions: A longer test time on the STS test result was associated with a higher occurrence of postoperative PJK. A cutoff value of 22 s can be suggested. Preoperative surveillance of these patients and providing additional efforts and surgical procedures for the prevention of PJK are anticipated to improve the surgical outcome of ASD correction.