"Risk factors for early-onset adjacent segment disease at L5-S1 segment after isolated L4-5 lumbar fusion surgery".

PURPOSE: This study aimed to elucidate the pre- and postoperative radiological risk factors for L5-S1 adjacent segment disease (ASD) after isolated L4-5 posterior or transforaminal lumbar interbody fusion (PLIF/TLIF) surgeries.

METHODS

A total of 152 patients with degenerative lumbar diseases who underwent isolated L4-5 PLIF/TLIF were retrospectively investigated and followed up for at least one year (mean 4.9 years) after surgery. Age, sex, body mass index (BMI), and JOA score for low back pain at surgery were recorded. Pre- and postoperative radiographic lumbosacral parameters were measured as follows: slippage at the L4-5 segment (Meyerding grade 1-4), pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), lumbar lordosis (LL), PI-LL, distal lumbar lordosis (DL), L1-sagittal vertical axis (L1SVA), L4-sagittal vertical axis (L4SVA), and the amount of distraction of the L4-5 disc height (ΔDH). Preoperative degeneration of the L5-S1 disc was evaluated according to Pfirrmann's classification and intervertebral vacuum phenomenon (VP).

RESULTS

L5-S1 ASD was found in 9 patients at 1 year postoperatively. Univariate analyses revealed that lower BMI; Meyerding grade > 1; preoperative L1SVA > L4SVA; and postoperative DL, L1SVA > L4SVA, and ΔDH were the risk factors for L5-S1 ASD. Multivariable Logistic analysis revealed that postoperative L1SVA > L4SVA was an independent risk factor for L5-S1 ASD.

CONCLUSION

The anterior shift of the lumbar loading axis with failed compensation indicated by L1SVA > L4SVA may be associated with the pathology of early-onset L5-S1 ASD after isolated L4-5 PLIF/TLIF.