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

Abstract

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.

Plain Language Summary

Decrease in Bone Mineral Density After Lateral Lumbar Interbody Fusion: Spine surgery can sometimes cause bone loss where the surgery is done. This study looked at a specific type of surgery called lateral lumbar interbody fusion (LLIF) and compared 2 ways it can be done: 1 with just the fusion (stand-alone LLIF) and 1 with extra screws and rods in the back (360° constructs). Doctors reviewed patients who had these surgeries between 2016 and 2024 and measured bone density in the bones above and below the surgery before and after the operation. The study included 72 patients, split evenly between the 2 types of surgery. Both groups lost some bone in the nearby bones after surgery. For patients with stand-alone LLIF, the loss was mainly in the bones above the surgery. For those with screws and rods, it happened above and below. However, when researchers compared the 2 groups, the amount of bone loss was about the same. This means that both types of surgery can cause bone loss in nearby bones, but adding screws and rods does not seem to make it worse.