Postoperative Decrease in Volumetric Bone Mineral Density in Patients Undergoing Anterior or Lateral Lumbar Interbody Fusion: Stand-Alone Versus 360° Constructs.

Background: Studies have shown that various types of spine surgery can be a contributing factor in bone loss, but the influence of lateral lumbar interbody fusion (LIF) on postoperative bone loss remains unclear. Purpose: We sought to investigate the influence of spine surgery, measured by quantitative computed tomography (QCT), on the adjacent vertebrae, and to evaluate the bone loss between stand-alone LIF (SA-LIF) and LIF supplemented with posterior pedicle screw-rod fixation (360° constructs). Methods: We conducted a retrospective review of the records of patients who underwent SA-LIF and 360° constructs between 2016 and 2024. Inclusion criteria were (1) the interval between surgery and the secondary CT was 2 to 12 months; (2) the interval between the preoperative and postoperative CT was a minimum of 2 months; (3) the patient did not undergo additional spine surgery between those 2 CT scans; and (4) volumetric bone mineral density (vBMD) measurements of 1 level above the upper vertebra (UV+1) were possible in all cases. We excluded levels with a corpectomy, planned staged surgery, more than 4 levels of fusion, and poor QCT imaging quality. Postoperative changes in vBMD in the vertebrae at UV+1, UV+2, and 1 level below the lower vertebra (LV-1) were measured. Pre- and postoperative vBMDs were compared. Postoperative vBMD changes were also compared between the 2 groups. Results: Out of 191 patients who underwent the anterior or lateral interbody fusion in the specified time period, 72 patients met our inclusion criteria (36 SA-LIF; 63.3 ± 15.1 years, 36 360° constructs; 58.6 ± 11.3 years). UV+1 and UV+2 showed significant decreases in the SA-LIF group, and UV+2 and LV-1 decreased significantly in the 360° group. In the ANCOVA adjusted for age, the percent change in vBMD at each adjacent level showed no significant difference between the 2 groups. Conclusion: Both SA-LIF and 360°construct surgeries negatively affected the postoperative vBMD values at adjacent levels. There was no statistically significant difference in bone loss between the 2 groups, suggesting that additional surgical invasiveness caused by screw insertion may not affect the severity of postoperative bone loss. Level of Evidence: Level III: retrospective cohort study.