Thoracolumbar deformity arthrodesis to L5 in adults: The fate of the L5-S1 disc

Study Design. A retrospective clinical and radiographic analysis of long adult deformity fusions terminating at L5. Objectives. To define the results of thoracolumbar fusions to L5 in adult deformity patients with critical evaluation for potential subsequent L5-S1 disc degeneration and L5 implant loosening. Summary of Background Data. Few studies have reported the results of long adult fusions to L5 and the potential for subsequent advanced L5-S1 disc degeneration is unknown. Materials and Methods. Thirty-four consecutive patients fused from the thoracic spine to L5 at a single institution were evaluated at a mean follow-up of 5.6 years (2.1-14.3 years). SRS-24 functional outcome questionnaire results were obtained for all patients at most recent follow-up. Results. By latest follow-up, subsequent advanced L5-S1 disc degeneration (SAD) developed in 19 of 31 patients (61%) assessed as having "healthy" discs before surgery. SAD was associated with a forward shift in sagittal balance (P = 0.02) and need for revision surgery (P= 0.02). Risk factors for the development of SAD were preoperative positive sagittal balance (P = 0.01), younger age (P = 0.03), and the presence of even mild radiographic degeneration before surgery (P = 0.004). Loss of L5 implant fixation occurred in six patients (18%) and was associated with deep seating of L5 within the pelvis (P = 0.0001). Inferior SRS-24 outcome measures were associated with preoperative advanced L5-S1 disc degeneration and the development of postoperative sagittal imbalance. Conclusions. Subsequent L5-S1 DDD developed in 61% of patients after long adult fusions to L5 and was associated with a significant loss of sagittal alignment and an increased likelihood for or definite need for another operation. Loss of L5 implant fixation is not uncommon, especially in patients with a deep-seated L5 vertebra.