Distal Junctional Kyphosis (DJK) Adolescent Idiopathic Thoracic Curves Following Anterior or Posterior Instrumented Fusion: Incidence, Risk Factors and Prevention

• a - DePuy Spine

Purpose: Purpose: Analyze pre and postoperative radiographic parameters of patients with thoracic adolescent idiopathic scoliosis (AIS) associated with DJK.

Objectives: Determine the incidence of DJK pre and postoperatively in AIS patients undergoing either anterior or posterior thoracic fusion. Identify “risk factors” for development of DJK and provide recommendations for prevention.

Summary of Background Data: The incidence of DJK is unknown as are risk factors.

Methods: This is a retrospective multicenter analysis of a subset of 379 patients with thoracic AIS treated by either anterior (139) or posterior (240) fusion with pre or postoperative DJK > 9°. Analysis included the Cobb and instrumented levels of the thoracic curves, sagittal measurements including T2-T5, T5-T12, T2- T12, T10-L2, T12-S1, and C7 plumbline, on preoperative and two-year follow-up standing radiographs.

Results: The mean age at surgery was 14.4 years (9.1-20.9) in the anterior group and 14.7 years (10.2-21.7) in the posterior group and the mean preoperative curve was 52° in the anterior and 54° in the posterior. 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 14.4% postoperatively. Of the measurements analyzed, T5-T12 and T10-L2 correlated positively with DJK. The T10-L2 region in the posterior group with preoperative DJK had a mean of + 20° preoperative kyphosis compared with -2° lordosis in the group as a whole. When postoperative DJK developed in the posterior group there was a +16° change and +2° change in the group as a whole (p=0.05). In the anterior group with preoperative DJK the mean preoperative T10-L2 was +8° compared to 0° for the anterior group as a whole. When postoperative DJK developed the mean postoperative T10-L2 was +12° kyphosis compared to +2° for the anterior group as a whole (p=0.007), and the mean change was an increased kyphosis of +6° and +2°, respectively (p=0.05). In the posterior group with postoperative DJK the mean preoperative sagittal T5-T12 was 31.2°, which was significantly higher than the preoperative measurement of 23.4° for the group without DJK (p=0.02). The distal instrumented levels in the anterior group with preoperative DJK was to Cobb +1 as opposed Cobb +0 in the group as a whole (p=0.07). In the posterior group with preoperative DJK, instrumentation was Cobb +2 compared to Cobb +1 in the group as a whole (p=0.09). In comparing each group without DJK, the posterior group was instrumented to Cobb >+1 and the anterior group was instrumented to Cobb +0 (p<0 .0001).

Conclusion: The incidence of DJK was twice as high in patients undergoing posterior versus anterior fusion for thoracic AIS. The presence of increased kyphosis preoperatively in the T5-T12 region, seen in the posterior group, and in the T10-L2 region seen in both groups constitute risk factors for the development of DJK and an indication for considering extension of distal fusion levels. It appears that posterior instrumentation for thoracic curves must extend a level longer distally than anterior instrumentation to prevent DJK when preoperative DJK is present.

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