Objectives:

To evaluate Hounsfield units (HU) at the adjacent segment after single-level transforaminal lumbar interbody fusion (TLIF) with pre- and post-operative CT scans.

Methods:

We performed a retrospective study on a series of patients who underwent L4-5 transforaminal lumbar interbody fusion (TLIF), from 2007 to 2017, by three spine surgeons at our institution. 143 total patients were identified and 41 patients with minimum 1-year follow-up met inclusion criteria. HU values were measured on preoperative and postoperative CT at the adjacent L3 segment and at L1 as a control arm. Lumbar lordosis, pelvic tilt, pelvic incidence, sacral slope, and sagittal vertical axis were also collected pre and postoperatively.

Results:

Mean pre-operative HU value at L3 did not differ from the post-operative value (134.11 +/- 47.14 mg/cm³ vs. 141.21 +/- 55.14 mg/cm³, p = 0.34). Similarly, the mean pre-operative HU value at the L1 control level ROI did not differ from the post-operative value (150.17 +/- 53.91 mg/cm³ vs. 145.78 +/- 58.34 mg/cm³, p = 0.634). The inter-rater reliability of HU measurements was satisfactory with a resulting intraclass correlation coefficient of 0.76.

Conclusion:

As measured by HU, we did not observe a change in bone density or other signs of adjacent segment disease at the L3 vertebral body 12 months following L4-5 TLIF. Spinopelvic parameters were not shown to be correlated with HU changes.