Reportage in the orthopedic surgery operating theatre in Pasteur 2 Hospital, Nice, France. Medullary liberation and arthrodesis in a patient suffering from lumbar stenosis caused by arthritis. The operation consists of freeing boney elements from the vertebral canal that are compressing it, and consolidating the spine with an arthrodesis. This operation is carried out using the pre-op 3D imagery O-Arm system. The scanner locates the fixed marker and creates new boney markers.