Intervertebral spacer to be placed between two adjacent, upper and lower cervical vertebrae, the spacer comprising a spacer body and retention member for retaining the spacer body in position against said vertebrae. The retention member includes a strap and fastener member that are removable and self-blocking, enabling the ends of the strap to be secured to the spacer body. The spacer body including: a spacer part having two opposite ends, a portion of the first end configured to be inserted between the vertebrae and top and bottom flanges connected via their bases to the second end of the spacer part and extending on either side thereof, each flange presenting an anterior face facing towards the spacer part and configured to bear against the posterior portion of the lamina of the upper or lower vertebra, respectively.
