Risk of Distal Junctional Kyphosis in Scheuermann's Kyphosis is Decreased by Selecting the LIV As Two Vertebrae Distal to the First Lordotic Disc

Purpose: To determine whether (1) distal junctional kyphosis (DJK) is decreased by selecting the stable sagittal vertebra (SSV), versus the vertebra below the 1st lordotic disc (1stLD), as the lowest instrumented level (LIV); (2) DJK is decreased if the LIV is two versus one vertebrae distal to the 1stLD.

Methods: A multi-institution prospective database was queried for SK patients who underwent posterior-only instrumentation and fusion with > 2 year follow-up. DJK was defined as > 10° change in the distal junctional angle postoperative from the preoperative junctional angle. Statistical analysis was performed using t test, chi-square test and logistic regression.

Results: Of 94 patients included, 38 (40%) developed radiographic DJK. 31 (39%) patients in whom the LIV was at or distal to the SSV developed DJK, whereas 7 (47%) in whom the LIV was proximal to the SSV developed DJK. 20 (59%) patients in whom the LIV was one vertebra below and 10 (22%) in whom the LIV was two vertebrae below the 1stLD developed DJK. Logistic regression demonstrated a significant increase in DJK development if the LIV was one vertebra below the 1stLD (OR = 3.2 (1.28-8.18)). There was not a significant relationship between DJK development and LIV position relative to the SSV.

Conclusion: In SK surgery, LIV selection/fusion to two vertebrae below the 1stLD decreased the development of DJK. A significant relationship was not found between DJK development and location of distal fusion level in regards to the SSV, possibly due to the small number of patients who had LIV proximal to SSV.