The Risk of Proximal Junctional Kyphosis Decreases in Patients With Optimal Thoracic Kyphosis.

Study

Design: A retrospective study of surgical outcomes.

Objective: This study aimed to investigate the preoperative risk factors for proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgery. Summary of background data: The cause of PJK is still unclear, although some risk factors have been reported in ASD surgery.

Methods: A total of 185 patients who were followed up for more than two years and underwent ASD surgery were recruited. PJK was defined as a proximal junctional angle ≥20° or reoperation due to PJK within two years after surgery. These patients were divided into PJK and non-PJK groups. Whole-spine standing radiography was performed before and immediately, one year, and two years after the surgery.

Results: The PJK and non-PJK groups comprised 58 and 127 cases, respectively. The incidence of PJK demonstrated significant differences according to preoperative thoracic kyphosis (TK): 37% (TK ≤19°), 33% (TK 20°-29°), 9% (TK 30°-39°), 32% (TK 40°-49°), and 41% (TK ≥50°) (p < .05). Logistic regression analysis suggested that the amount of change in TK before and just after the surgery (ΔTK) was a significant risk factor for PJK (p < .001; odds ratio 1.062, 95% confidence interval 1.029-1.097).

Conclusion: ΔTK was less in the TK group of 30°-39° because the TK of patients who underwent ASD surgery converged to 34.5° just after surgery. Consequently, a lower or higher TK was likely to result in a large ΔTK just after surgery. Therefore, patients who had an optimal TK (30°-39°) had a lower risk of PJK. Level of evidence: Level IV.