Large Difference Between Proximal Junctional Angle and Rod Contouring Angle is a Risk Factor for Proximal Junctional Kyphosis

Abstract

Objective: To assess the role of the difference between the proximal junctional angle (PJA) and rod contouring angle (RCA) (PJA-RCA) in the development of postoperative proximal junctional angle (PJK) in Lenke I and II adolescent idiopathic scoliosis (AIS) patients.

Methods: We performed a retrospective analysis of 84 Lenke I and II AIS patients who underwent posterior segmental spinal instrumentation and fusion between 2012 and 2018 (minimum follow-up of 1.5 years and an average follow-up of 2 years) at a single institution. The full-spine x-ray films taken at the preoperative, postoperative, and final follow-ups were measured for each patient. The radiographic parameters were compared between the PJK and non-PJK groups, and binary logistic regression with forward elimination (conditional) was also performed to identify the risk factors for the occurrence of PJK.

Results: Among the 84 patients (mean age: 14.63 ± 1.33 years), the overall incidence of PJK was 23.81%. The PJK group showed a larger preoperative pelvic incidence (55.66° ± 8.66° vs. 50.29°±8.27°, P = 0.045), thoracic kyphosis (TK) (32.44° ± 5.60° vs. 27.19° ± 5.14°, P = 0.007) and sagittal vertical axis (SVA) (40.99 ± 21.82 mm vs. 18.13 ± 28.64 mm, P = 0.013) than the non-PJK group. Postoperatively, the PJK group showed a larger decrease in the TK (-10.62° ± 3.19° vs. -5.56° ± 1.17°, P < 0.001) and SVA (-24.28 ± 18.22 mm vs. -10.83 ± 15.02 mm, P = 0.007). In addition, the PJK group had significantly larger postoperative PJA (9.83° ± 2.64° vs. 5.77° ± 3.06°, P < 0.001) and postoperative PJA-RCA (6.56° ± 3.69° vs. 1.55° ±3.32°, P < 0.001). The proportion of patients with a PJA-RCA value greater than 5° was significantly larger in the PJK group (65.00% vs. 18.75%, P < 0.001). At the last follow-up, the PJK patients had significantly larger TK (35.11° ± 5.51° vs. 26.53° ± 4.71°, P < 0.001) and SVA (22.83 ±23.12 mm vs. 3.46 ±26.24 mm, P = 0.038). Binary logistic regression analysis showed that decreases in TK and postoperative PJA-RCA were the primary contributors to PJK in patients with AIS.

Conclusions: Large postoperative PJA-RCA and decreased TK are risk factors for PJK in Lenke I and II AIS patients, especially those with PJA-RCA greater than 5°, and the occurrence of PJK should be highly considered.

Keywords: Adolescent idiopathic scoliosis; Proximal junctional angle; Proximal junctional kyphosis; Rod contouring angle.