The prevalence of distal junctional kyphosis following posterior instrumentation and arthrodesis for adolescent idiopathic scoliosis

Distal junctional kyphosis (DJK) is a radiographic finding in patients that undergo spinal instrumentation and fusion, since there is an abrupt transition between fixed and mobile spinal segments.The true incidence of DJK is variable in literature and seems that has a multifactorial etiology. A consecutive series of 130 patients (mean age 15.6 years) with adolescent idiopathic scoliosis who underwent posterior spinal fusion and instrumentation were evaluated by analyzing coronal and sagittal angulation and balance measurements from standing radiographs obtained pre-operatively, within 6 weeks post-operation, at two years postoperative and at the latest follow-up. There was 35 male and 95 female. The mean time of follow-up was 36 months. The incidence of DJK at latest follow-up was 6.9% (9 patients). In DJK group, distal junctional angle from pre-operative of -12.5° lordosis (-30 to 0) reached to -5.5° (P=0.015) at 6 weeks postoperation and to -1.4° (-20 to 12°) (P=0.000) at 2 years follow-up,with mean of 12.1° kyphotic change (10-20°). In non DJK group, distal junctional angle from pre-operative angle of -7.5° reached -8.1° at 2 years follow-up (P=0.43). The mean age of DJK group at surgery was 17 years and for non-DJK group was 15.4 years (P=0.022). Distal junctional kyphosis was less common in this study than previous reports and stabilized after two years. The magnitude of coronal cobb angles or multiplicity of coronal curves had no effect in developing DJK that may be prevented by incorporation of the first lordotic disc into the fusion construct.