Adjacent Vertebral BMD Decline After Lateral Lumbar Interbody Fusion

Lateral lumbar interbody fusion technology may have a protective effect on the paravertebral and spinal ligaments during surgery, resulting in positive effects on bone mineral density (BMD). However, evidence is lacking on the change in vertebral bone density of patients. The changes in bone density in patients after lumbar fusion surgery are closely related to the occurrence of mechanical complications such as proximal border kyphosis, screw extraction, and adjacent vertebral fractures. Therefore, the aim is to investigate the changes in the volumetric bone mineral density (vBMD) of the adjacent vertebral cancellous bone and endplate at the fusion level in patients undergoing lateral lumbar interbody fusion (LLIF).

The medical records of patients with lumbar degenerative diseases who underwent LLIF surgery in our hospital from March 2018 to October 2021 were retrospectively examined. The volumetric BMD of the cancellous bone and endplate adjacent to the lumbar fusion segment was measured before the operation and during postoperative follow-up. The measured volumetric BMD included the level of the upper/lower instrumented vertebra and the endplate (UIV + 1; LIV + 1; UIV + 1e; and LIV + 1e). Shapiro-Wilk test, one-way ANOVA, Mann-Whitney test, Fisher exact test, univariable, and receiver operating characteristic (ROC) curve analysis were executed in this study.

A total of 32 patients were included in the study, including 27 women and 5 men, with a mean age of 60.1 ± 7.1 years. The preoperative vBMD values in the UIV + 1, LIV + 1, UIV + 1e, and LIV + 1e groups were greater than those at the postoperative follow-up (131.9 ± 34.8 vs. 115.8 ± 30.8; 134.8 ± 37.0 vs. 117.2 ± 32.1, p < 0.001; 312.9 ± 79.3 vs. 287.7 ± 85.2, p = 0.007; 314.7 ± 71.4 vs. 296.1 ± 59.8, p = 0.042). The vBMD changes and rates of change in the cancellous and endplate regions were 16.1% ± 17.7% (11.4% ± 13.0%), 12.2% ± 12.1% (17.3% ± 17.5%), 11.4% ± 18.3% (-25.2% ± 49.2%), and 7.2% ± 18.5% (-18.6% ± 49.8%) in the UIV + 1, LIV + 1, UIV + 1e, and LIV + 1e groups, respectively. There was no significant difference in the preoperative vBMD, postoperative vBMD, or percent vBMD change between UIV + 1 and LIV + 1. However, there was a significant difference in the endplate vBMD at follow-up (p = 0.035).

We evaluated the changes of vBMD of the cancellous bone and endplates adjacent to the vertebral body, cephalad or caudal to the fused level in LLIF patients through QCT, and can provide a new approach for reducing the occurrence of mechanically related complications after vertebral fusion surgery.