Risk Factors of Proximal Junctional Kyphosis in Adolescent Idiopathic Scoliosis – the Spinous Processes and Proximal Rod Contouring

Proximal Junctional Kyphosis (PJK) as one of the most discussed problems after corrective surgery in adolescent idiopathic scoliosis (AIS), is still not fully clarified and seems to be multifactorial. Biome-chanical and few clinical studies have shown the influence of destruction of posterior ligaments by re-section of spinous processes and some parameters concerning rod contouring as risk factors for PJK. To verify these results 192 patients with AIS and corrective surgery via posterior approach between 2009 and 2017 were included. Radiographic parameters were analyzed preoperatively (preOP), postoperatively (postOP), and with a mean follow up (FU) of 27 months. The participants were divided into two groups (PJK group and non-PJK group). The incidence of PJK was 15.6%. Contrary to the results of biomechanical studies, we could not find any significant influence of the spinous process resection. However, the PJK group had significantly larger preOP T4-T12 kyphosis (31.1°±13.93° vs. 23.3°±14.93°, p=.016). Furthermore, the PJK group showed a significantly larger rod contour angle (RCA) (8.0°±4.44° vs. 5.9°±3.28°, p=.003) and mismatch of postOP proximal junctional angle (PJA) and RCA (3.5°±5.72° vs. 0.9°±4.86°, p=.010) compared to the non-PJK group. An increase of the mismatch of postOP PJA and RCA (OR=1.14, p=.008) and a high RCA are risk factors for PJK and need to be focused on by surgeons.