Instrumented lumbar fusion surgery is often accompanied by interbody fusion using an autologous bone graft that is supposed to expand and remodel to achieve a rigid and lasting bony construction between two vertebrae. However, there is a dearth of knowledge regarding the process of biological remodelling of intercorporal bone grafts. Also, a valid and reliable assessment of fusion status remains challenging because there is no objective tool available to quantify the bone remodelling process. CT-based Hounsfield Units correlate with Bone Mineral Density and can be used as a proxy to establish trajectories over time to assess changes in bone mineral density from the bone graft.