Diagnosing the Undiagnosed: Osteoporosis in Patients Undergoing Lumbar Fusion.

Study Design: Retrospective analysis.
Objective: The aim of the study was to report the incidence of undiagnosed osteoporosis in patients undergoing lumbar spine fusion using computed tomography (CT) Hounsfield units (HU).
Summary of Background Data: We used a recent technique utilizing HU to estimate bone mineral density (BMD) of the lumbar spine and hypothesized that this technique would reveal a high percentage of undiagnosed osteoporotic patients undergoing transforaminal lumbar interbody fusion (TLIF).
Methods: We reviewed patients older than 50 years undergoing TLIF from a single-center and multiple surgeons. We determined the mean HU of L4 on axial CT. Average HU values for patients with diagnosed lumbar osteoporosis (DEXA BMD <0.75 g/cm) were compared to patients with osteopenia and normal BMD (between 0.75 and 0.9 g/cm and >0.9 g/cm, respectively). The percentage of patients with HU values consistent with osteoporosis, but without any formal evaluation, was also calculated.
Results: Over 10 years, 143 patients older than 50 years underwent TLIF, and 128 had available perioperative lumbar CT scans. Men and Women comprised 60.2% and 39.8% of the population, respectively. Average age was 61.5 years (range: 50.0-83.5 years). Twenty-nine patients had both dual-energy X-ray absorptiometry and CT data available for analysis. There was a significant association with decreased HU in patients with lumbar BMD less than 0.75 g/cm (105.6 HU, 95% confidence interval [CI] 6.76) in comparison to patients with osteopenia (146.0 HU, 95% CI 4.09) and with normal BMD (165.9, 95% CI 21.35). Ten men (7.8%) and 15 women (11.7%) had HU values consistent with osteoporosis. Sixty-four percent of patients with osteoporotic HU values had never been formally evaluated for the disease.
Conclusion: HU may be an alternative to screening preoperative dual-energy X-ray absorptiometry scan and can minimize costs and resource utilization. We found a large proportion of patients older than 50 years undergoing TLIF had HU levels consistent with undiagnosed osteoporosis of the lumbar spine.
Level of Evidence: 4.