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

Abstract

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. 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). 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. 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. 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 III: retrospective cohort study.