Proximal junctional kyphosis in adolescent idiopathic scoliosis following segmental posterior spinal instrumentation and fusion - Minimum 5-year follow-up

Study Design. A retrospective study. Objective. To analyze the long-term proximal junctional change in adolescent idiopathic scoliosis (AIS) following segmental posterior spinal instrumentation and fusion 5 years or more after surgery. Summary of Background Data. No study has concentrated on time-dependent long-term proximal junctional change in AIS following segmental posterior spinal instrumentation and fusion after 5 years postoperation. Risk factors for developing proximal junctional kyphosis (PJK) are unknown. Methods. A total of 193 consecutive AIS patients with a minimum 5-year follow-up (Average, 7.3 years; range, 5-16.7 years) treated with segmental posterior spinal instrumentation and fusion were evaluated. Radiographic measurements analyzed included sagittal Cobb angle at the proximal junction on preoperative, early postoperation, 2-year postoperation, and final follow-up (>= 5 years) by standing long cassette radiographs. Postoperative Scoliosis Research Society (SRS)-24 outcome scores were also evaluated. Abnormal PJK was defined as the final proximal junctional sagittal Cobb angle between the lower endplate of the uppermost instrumented vertebra and the upper endplate of two vertebrae supra-adjacent, which was >10 degrees and at least 10 degrees greater than the preoperative measurement. Results. The incidence of PJK at 7.3 years postoperation was 26% (50 of 193 patients). The average proximal junctional angle increased 15.2 until 2 years postoperation and then increased 1.7 degrees until final follow-up in the PJK group (n=50). Factors that were statistically significant for PJK development were as follows: a thoracoplasty procedure (P=0.001), preoperative hyperkyphotic thoracic alignment (T5-T12>40 degrees) (P=0.015), and hybrid instrumentation (proximal hooks and distal pedicle screws) compared with the hooks only group (P=0.029). The number of fused vertebrae more than 11 was also related with PJK (P=0.08). The level of the uppermost instrumented vertebra did not affect the PJK incidence. SRS-24 outcome scores did not demonstrate any significant differences (P=0.54 for total score and P=0.49 for self-image subscale) between the PJK and non-PJK groups. Conclusion. The incidence of proximal junctional kyphosis at 7.3 years postoperation was 26% and did not progress significantly after 2 years postoperation. Risk factors for developing PJK were an associated thoracoplasty, hybrid instrumentation (proximal hooks and distal pedicle screws), and a preoperative larger sagittal thoracic Cobb angle (T5-T12>40 degrees). The SRS-24 outcome instrument was not affected by PJK.