Adjacent Segment Vertebral Body Bone Density Changes as Measured By Hounsfield Units After Lumbar Spine Fusion

We sought to evaluate Hounsfield units (HU) at the adjacent segment after single-level transforaminal lumbar interbody fusion (TLIF) with preoperative and postoperative computed tomography scans. We performed a retrospective study on a series of patients who underwent L4-5 TLIF, from 2007 to 2017, by 3 spine surgeons at our institution. One-hundred and forty-three total patients were identified, and 41 patients with minimum 1-year follow-up met inclusion criteria. HU values were measured on preoperative and postoperative computed tomography 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 preoperatively and postoperatively. Mean preoperative HU value at L3 did not differ from the postoperative value (134.11 ± 47.14 mg/cm3 vs. 141.21 ± 55.14 mg/cm3, P = 0.34). Similarly, the mean preoperative HU value at the L1 control level region of interest did not differ from the postoperative value (150.17 ± 53.91 mg/cm3 vs. 145.78 ± 58.34 mg/cm3, P = 0.634). The interrater reliability of HU measurements was satisfactory with a resulting intraclass correlation coefficient of 0.76. 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 after L4-5 TLIF. Spinopelvic parameters were not shown to be correlated with HU changes.