Mismatch Between Proximal Rod Contouring and Proximal Junctional Angle A Predisposed Risk Factor for Proximal Junctional Kyphosis in Degenerative Scoliosis

Study Design. A retrospective study. Objective. To investigate whether the mismatch between proximal junctional angle (PJA) and the proximal rod contouring contributed to the occurrence of postoperative proximal junctional kyphosis (PJK) in degenerative scoliosis. Summary of Background Data. PJK is one of the complications in the treatment of degenerative scoliosis, the postoperative PI-LL mismatch and the increased rod stiffness are supposed to be the etiology of PJK. However, the impact of rod contouring on PJK has not been fully illustrated. Methods. A retrospective study was performed on 27 consecutive degenerative scoliosis patients (three males and 24 females) who underwent corrective surgery with more than 2-year follow-up. Radiographic parameters included proximal rod contouring angle (PRCA) and PJA at the three time-points. The subjects were divided into two groups: PJK group and non-PJK group with the definition of PJK as a PJA more than 10 degrees. The mismatch between PRCA and post-op PJA, defined as the difference between PRCA and postop PJA of more than 5 degrees, was then compared with PJK and non-PJK group. Results. The patients' mean age was 60.48 +/- 6.47 years old with a mean Cobb angle of 40.89 +/- 14.33 degrees. Twelve patients, with a mean PJA of 18.67 +/- 5.31 degrees at the last followup, were stratified into the PJK group, while the remaining 15 patients, with a mean PJA of 5.33 +/- 2.47, were placed into the non-PJK group. A significant difference in the mismatch between post-op PJA and PRCA was observed between PJK and non-PJK group (8.83 +/- 5.07 degrees vs. 4.07 +/- 2.91 degrees, P = 0.005). Meanwhile the difference of mismatch between preop PJA and PRCA showed no statistical significance (5.16 +/- 4.24 degrees vs. 3.00 +/- 2.48 degrees, P = 0.109). Conclusion. Mismatch between rod contouring and postoperative proximal spinal curve may be a predisposed risk factor for PJK in degenerative scoliosis.