Distal junctional kyphosis of adolescent idiopathic thoracic curves following anterior or posterior instrumented fusion: Incidence, risk factors, and prevention

Study Design. This is a retrospective multicenter analysis of a subset of 375 patients with thoracic adolescent idiopathic scoliosis (AIS) treated with either anterior (238) or posterior (137) fusion with preoperative or postoperative distal junctional kyphosis (DJK) >= 10 degrees. Objectives. To determine the incidence of DJK before and after surgery in patients with AIS undergoing either anterior or posterior thoracic fusion, and provide recommendations for prevention. Summary of Background Data. DJK following surgical treatment for AIS may result in pain, imbalance, and unacceptable deformity. The true incidence of DJK following selective anterior or posterior instrumentation and fusion is unknown, as are "risk factors" for its development. Methods. Mean age at surgery was 14.4 years (range 9.1-20.9) in the anterior group and 14.7 years (range 10.2-20.7) in the posterior. Analysis included the Cobb and instrumented levels of the thoracic curves, and sagittal measurements, all on preoperative and 2-year follow-up standing 36-in radiographs. Results. In the anterior group, the incidence of preoperative DJK was 4.2%, and postoperative DJK was 7.1%. In the posterior group, the incidence of preoperative DJK was 5.0% and 14.6% after surgery. When postoperative DJK developed in the posterior group, mean postoperative T10-L2 was +17 degrees kyphosis compared to +2 degrees in the posterior group without DJK (P < 0.001). When postoperative DJK developed in the anterior group, mean postoperative T10-L2 was +12 degrees kyphosis compared to +2 degrees for the anterior group without DJK (P = 0.006). DJK was significantly more likely to occur in the posterior group if the Cobb was instrumented to less than Cobb +1 (P < 0.001). Conclusions. It appears that both posterior and anterior instrumentation for thoracic curves must include the junctional level to prevent postoperative DJK when postoperative DJK is present. The presence of increased kyphosis after surgery in the T10-L2 region seen in both anterior and posterior groups that had postoperative DJK develop constitutes a "risk factor" for the development of DJK.