Usability of a novel Hounsfield units measurement procedure to quantify intercorporal bone graft remodeling in patients after posterior lumbar interbody fusion: a case series

Background: There is a lack of knowledge about the biological process of intercorporal bone graft remodeling after posterior lumbar interbody fusion surgery and whether this process is associated with changes in back pain and intercorporal fusion status. As an alternative to the commonly used but unreliable fusion criteria, Hounsfield units can be used to quantify biological activity and changes in bone mineral content. However, studies assessing Hounsfield units conducted to date do not provide sufficient details about how the bone grafts were segmented to measure the Hounsfield units to allow for replication, and did not assess individual patient trends in graft changes over time. Using the data of nine patients after posterior lumbar interbody fusion, a novel Hounsfield units measurement procedure was developed and used to explore its usability to quantify the bone graft remodeling process. Case details: We report a case series of nine patients (six male, three female, mean age 64 years, all Caucasian) who all had computed tomography scans performed at 1 and 2 years after posterior lumbar interbody fusion surgery. Overall, seven out of the nine (78%) cases had a 3–41% increase in their bone grafts’ Hounsfield units between 1 and 2 years after surgery. The cases showed large interindividual variability in their Hounsfield units values over time, which coincided with varying levels of back pain and intercorporal fusion status. Conclusion: The Hounsfield units measurement procedure used for this case series may be useful to quantify intercorporal bone graft remodeling in patients after posterior lumbar interbody fusion, and may be used as an adjunct diagnostic measure to monitor bone graft remodeling over time. Future research is warranted to explore how to interpret bone graft Hounsfield units-values and Hounsfield units trajectories in light of clinical variables or intercorporal fusion status.