The standing T1–L1 pelvic angle: a useful radiographic predictor of proximal junctional kyphosis in adult spinal deformity

Abstract

OBJECTIVE Proximal junctional kyphosis (PJK), which can worsen a patient’s quality of life, is a common complication following the surgical treatment of adult spinal deformity (ASD). Although various radiographic parameters have been proposed to predict the occurrence of PJK, the optimal method has not been established. The present study aimed to investigate the usefulness of the T1–L1 pelvic angle in the standing position (standing TLPA) for predicting the occurrence of PJK. METHODS The authors retrospectively extracted data for patients with ASD who underwent minimum 5-level fusion to the pelvis with upper instrumented vertebra between T8 and L1. In the present study, PJK was defined as ≥ 10° progression of the proximal junctional angle or reoperation due to progressive kyphosis during 1 year of follow-up. The following parameters were analyzed on whole-spine standing radiographs: the T1–pelvic angle, conventional thoracic kyphosis (TK; T4–12), whole-thoracic TK (T1–12), and the standing TLPA (defined as the angle formed by lines extending from the center of T1 and L1 to the femoral head axis). A logistic regression analysis and a receiver operating characteristic curve analysis were performed. RESULTS A total of 50 patients with ASD were enrolled (84% female; mean age 74.4 years). PJK occurred in 19 (38%) patients. Preoperatively, the PJK group showed significantly greater T1–pelvic angle (49.2° vs 34.4°), conventional TK (26.6° vs 17.6°), and standing-TLPA (30.0° vs 14.9°) values in comparison to the non-PJK group. There was no significant difference in the whole-thoracic TK between the two groups. A multivariate analysis showed that the standing TLPA and whole-thoracic TK were independent predictors of PJK. The standing TLPA had better accuracy than whole-thoracic TK (AUC 0.86 vs 0.64, p = 0.03). The optimal cutoff value of the standing TLPA was 23.0° (sensitivity 0.79, specificity 0.74). Using this cutoff value, the standing TLPA was the best predictor of PJK (OR 8.4, 95% CI 1.8–39, p = 0.007). CONCLUSIONS The preoperative standing TLPA was more closely associated with the occurrence of PJK than other radiographic parameters. These results suggest that this easily measured parameter is useful for the prediction of PJK.

The Role of Thoracic Tilt in Identifying Thoracic Compensation and Predicting Proximal Junctional Kyphosis in Degenerative Lumbar Scoliosis

“…A recent study reported that the standing TLPA was closely associated with PJK. 32 However, there was scant analysis of postoperative thoracic inclination in that study. In the present study, higher postoperative TT and postoperative PJA were identified to be risk factors of PJK in the multivariate logistic regression model.…”

“…For patients with DLS who underwent long-segment corrective surgery, the thoracic spine is the major component of the unfused spinal segments, thus playing a paramount role in the development of PJK. A recent study reported that the standing TLPA was closely associated with PJK 32 . However, there was scant analysis of postoperative thoracic inclination in that study.…”

“…Similarly, there was no significant difference of preoperative TK and GTK between the PJK group and the non-PJK group in our study. Therefore, evaluation of thoracic spine has been extended to not only the magnitude of kyphotic angle but also thoracic flexibility, 26–28 thoracic distribution, 22,29,30 and thoracic inclination 31,32 …”

“…Therefore, evaluation of thoracic spine has been extended to not only the magnitude of kyphotic angle but also thoracic flexibility, [26][27][28] thoracic distribution, 22,29,30 and thoracic inclination. 31,32 Reciprocal changes of thoracic shape in degenerative lumbar deformity remain understudied. In this study, the thoracic shape was compared between patients with DLS and asymptomatic elderly controls with matched mean age and PI.…”