Evaluation of Proximal Junctional Kyphosis in Adolescent Idiopathic Scoliosis Following Pedicle Screw, Hook, or Hybrid Instrumentation

Study Design. Retrospective review. Objective. To compare the incidence of and risk factors for proximal junctional kyphosis (PJK) in adolescent idiopathic scoliosis (AIS) following posterior spinal fusion using hook, pedicle screw, or hybrid constructs. Summary of Background Data. Proximal junctional kyphosis is a recently recognized phenomenon in adults and adolescents after AIS surgery. The postoperative effect on PJK with the use of hooks, hybrid constructs, or screws has not been compared in a multicenter study to date. Methods. From a multicenter database, the preoperative and 2-year follow-up radiographic measurements from 283 patients with AIS treated with posterior spinal fusion using hooks (group 1, n = 51), hybrid constructs (group 2, n = 177), pedicle screws (group 3, n = 37), and pedicle screws with hooks only at the top level (group 4, n = 18) were compared. Results. The average proximal level kyphosis at 2 years after surgery was 8.2 degrees (range -1 to 18) in the all screw constructs, representing a significant increase when compared with hybrid and all hook constructs, 5.7 degrees (P = 0.02) and 5.0 degrees (P = 0.014), respectively. Conversely, average postoperative T5-T12 kyphosis was significantly less (P = 0.016) in the screw group compared with the all hook group. Of potential interest, but currently not statistically significant, was the trend towards a decrease in proximal kyphosis in constructs with all pedicle screws except hooks at the most cephalad segment, 6.4. The incidence of PJK (assuming PJK is a kyphotic deformity greater than 15) was 0% in group 1, 2.3% in group 2, 8.1% in group 3, and 5.6% in group 4 (P = 0.18). Patients with PJK had an increased body mass index compared with those who did not meet criteria for PJK (P = 0.013). Conclusion. Adjacent level proximal kyphosis was significantly increased with pedicle screws, but the clinical significance of this is unclear. A potential solution is the substitution of hooks at the upper-instrumented vertebrae, but further investigation is required.