The invention provides an intervertebral implant for the lumbo-sacral joint, the implant consisting in a spacer suitable for being placed between the fifth lumbar vertebra and the sacral vertebra articulated thereto, the body of said spacer presenting in its top face a groove extending in the midplane of the spacer and suitable for receiving the spinous process of said lumbar vertebra. A longitudinal housing oriented orthogonally to said groove is formed in the bottom face and is suitable for receiving the top portion of the sacral vertebra. The longitudinal housing is defined by an extension and by a tab of width narrower than the width of the body of the spacer. The section of the housing in the midplane of the space is generally U-shaped, being inclined relative to the bottom of the groove.