Abstract
Background: There are several risk factors for proximal junctional kyphosis (PJK) in adolescent idiopathic scoliosis (AIS) surgery. Decreased rod contouring angle (RCA) has been proposed as a risk factor for PJK, but the role of difference between proximal junctional angle (PJA) and RCA (PJA-RCA) has not been fully investigated. The aim of this study was to assess the role of PJA-RCA for the development of postoperative PJK in AIS. Methods: We performed a retrospective analysis of 96 AIS patients who underwent posterior segmental spinal instrumentation and fusion between the years 2012 and 2018 (minimum 1.5-year and average 2-year follow-up) at a single institution. Each patient was measured on preoperative, postoperative and final follow-up long-cassette standing radiographs. The PJA-RCA was regarded as a new definition that reflects the match degree between proximal rod contouring and vertebra curvature, and radiographic parameters were compared between PJK and non-PJK group. Results : Among the 96 patients with a mean age of 14.00 years (± 0.82), the overall incidence of PJK was 22%. PJK group showed a significantly greater preoperative SVA (P = 0.032) and larger correction of SVA (P = 0.007) than non-PJK group. At the last follow-up, PJK patients had significantly greater LL (P = 0.046). Patients in the PJK group had significantly greater preoperative PJA-RCA than the non-PJK group (4.07±3.30 vs. 1.42±4.28, P = 0.024). However, RCA was not significantly different between two groups (3.88 ± 4.34 vs. 2.86 ± 3.36, P = 0.405). In addition, Pearson correlation coefficient showed a significant correlation between the change of SVA and the last follow-up PJA (r = -0.208, P = 0.042). Preoperative PJA-RCA and postoperative PJA-RCA demonstrated similar results which showed a strong correlation with the last follow-up PJA (r = 0.528 and r = 0.532 respectively, P < 0.000). Conclusions: As a new reflex of improper rod contouring, large PJA-RCA is a risk factor for PJK in AIS, and PJK might be a compensation mechanism rather than complication when spine is shifted and overcorrected. Keywords: adolescent idiopathic scoliosis, proximal junctional kyphosis, proximal junctional angle, rod contouring angle.
Effects of multilevel posterior ligament dissection after spinal instrumentation on adjacent segment biomechanics as a potential risk factor for proximal junctional kyphosis: a biomechanical study