Expandable cage for the interbody fusion of lumbar vertebrae

An expandable cage for intercorporal fusion of lumbar vertebrae comprises a main body with two expandable parallel arms. Each arm has a supporting surface pointing outside and configured to contact an adjacent vertebral body, a groove pointing inside and extending along a transverse direction, and a channel pointing inside and extending along a longitudinal direction. An expansion element is instrument actuated and presses the arms apart expanding the cage. The expansion element is between the arms and comprises a cylindrical base body, two opposing radially aligned ribs on the base body, and a rectangular plate. Both the base body and ribs have curved, pair-wise opposed bearing surfaces. Depending on the cage's expansion state, either the base body bearing surfaces or the rib bearing surfaces contact channels provided in the arms, while the plate engages in the grooves of the arms.