The mechanism in junctional failure of thoraco-lumbar fusions. Part II: Analysis of a series of PJK after thoraco-lumbar fusion to determine parameters allowing to predict the risk of junctional breakdown.

PURPOSE

To identify risk factors, in 12 patients with junctional breakdown (JBD) after thoraco-sacral fusions and to test a software locating maximal bending moment on full spine EOS images.

METHODS

Twelve patients underwent long fusions for lumbar degenerative pathologies. Preop EOS images were compared to first postop EOS showing JBD. Parameters analyzed were: spinopelvic parameters [pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), sagittal vertical axis (SVA), spinosacral angle (SSA), lordosis, and kyphosis], proximal junctional angle (PJA), odontoid-hip axis angle (ODHA), and CIA. A new software estimated the location of maximum bending moment (M ) before and after JBD.

RESULTS

All patients except one had a JBD located between T10 and L1, diagnosed at average follow-up of 18.58 months. JBD was a fracture in six patients, severe adjacent disc degeneration in the remaining. Average PI was 52°. PT increased, SS decreased after JBD versus preop (p > 0.05). Average PJA was 34.5°. Global lordosis (GLL), upper lordosis (ULL), L4-S1 lordosis, and thoracic kyphosis (TK) were increased (p < 0.05). Lower lumbar lordosis (LLL), was not increased postJBD (p = 0.6). SVA, SSA, ODHA, and C7 slope were not modified (p > 0.05). CIA average value decreased by 7.5% after JBD. T1-T5 alignment was correlated to C7 slope before (R  = 0.77075) and after JBD (R  = 0.85409). ODHA decreased after JBD (p > 0.05). Most JBD occurred at or one level away from preoperative M location.

CONCLUSION

This study confirms the importance of harmonious distribution of lumbar (GLL, ULL, and ILL) and thoracic curves (TK, T1-T5 segment) in thoraco-sacral fusions. All patients showed an exaggerated ULL, resulting in a posterior shift and increased lever arm at the thoraco-lumbar junction, leading to JBD.