Height, Not Weight, is an Independent Predictor of Proximal Junctional Kyphosis After Adult Spinal Deformity Surgery

Study Design. – Retrospective review of prospectively collected, multicenter data. Objective. – To assess associations between patient height and weight independently and interactively with the incidence of proximal junctional kyphosis (PJK) after surgical treatment of adult spine deformity. Summary of Background Data. – Body mass index has traditionally been used to assess the influence of body composition on surgical outcomes, but the individual effects of height and weight have not been studied in relation to PJK. Methods. – We compared baseline demographic characteristics, radiographic measurements, and perioperative variables between patients who developed PJK after adult spinal deformity surgery between 2008 and 2020 and those who did not. Using a generalized additive model with a logistic link function, we modeled height and weight and their interaction as smooth terms to capture potential nonlinear effects on PJK risk. Multivariate analysis was adjusted for age, history of osteoporosis, upper instrumented vertebra, number of levels fused, and postoperative pelvic incidence minus lumbar lordosis and T1 pelvic angle. Results. – Of 904 included patients, the median age was 65 years (interquartile range: 58–71), and 76% were female. PJK developed in 131 patients (14%). Baseline characteristics, including frailty, comorbidities, and radiographic measures, did not differ significantly between the PJK and non-PJK groups. Taller height was a predictor of PJK (P=.03). In contrast, weight was not an independent predictor, and there was no significant interaction between height and weight. The incidence of PJK peaked at a height of approximately 179 cm before plateauing. Conclusions. – Taller height, but not weight, was associated with developing PJK after adult spinal deformity surgery. These findings underscore the importance of considering patient height during surgical planning.