Postoperative Radiographic Early-Onset Adjacent Segment Degeneration after Single-Level L4-L5 Posterior Lumbar Interbody Fusion in Patients without Preoperative Severe Sagittal Spinal Imbalance.

Study Design: Retrospective study.
Purpose: To investigate the relationship between preoperative total spinal sagittal alignment and the early onset of adjacent segment degeneration (ASD) after single-level posterior lumbar interbody fusion (PLIF) in patients with normal sagittal spinal alignment.
Overview of Literature: Postoperative early-onset ASD is one of the complications after L4-L5 PLIF, a common surgical procedure for lumbar degenerative disease in patents without severe sagittal imbalance. A better understanding of the preoperative characteristics of total spinal sagittal alignment associated with early-onset ASD could help prevent the condition.
Methods: The study included 70 consecutive patients diagnosed with lumbar degenerative disease who underwent single-level L4-L5 PLIF between 2011 and 2015. They were divided into two groups based on the radiographic progression of L3-L4 degeneration after 1-year follow-up: the ASD and the non-ASD (NASD) group. The following radiographic parameters were preoperatively and postoperatively measured: sagittal vertebral axis (SVA), thoracic kyphosis (TK), lumbar lordosis, pelvic tilt, and pelvic incidence (PI).
Results: Eight of the 70 patients (11%) experienced ASD after PLIF (three males and five females; age, 64.4±7.7 years). The NASD group comprised 20 males and 42 females (age, 67.7±9.3 years). Six patients of the ASD group showed decreased L3-L4 disc height, one had L3-L4 local kyphosis, and one showed both changes. Preoperative SVA, PI, and TK were significantly smaller in the ASD group than in the NASD group (p <0.05).
Conclusions: A preoperative small SVA and TK with small PI were the characteristic alignments for the risk of early-onset ASD in patients without preoperative severe sagittal spinal imbalance undergoing L4-L5 single-level PLIF.