An intervertebral spacer , comprising: a main body comprising: an exterior proximal wall , an exterior distal wall , a first exterior lateral wall , a second exterior lateral wall , an upper surface , a lower surface , a first interior lateral wall extending from the upper surface to the lower surface, a second interior lateral wall extending from the upper surface to the lower surface, an interior proximal wall extending from the upper surface to the lower surface and adjacent the first interior lateral wall and the second interior lateral wall, an interior distal wall extending from the upper surface to the lower surface and adjacent the first interior lateral wall and the second interior lateral wall, a longitudinal axis extending through planes containing the upper surface and the lower surface and through a geometric centre of the main body, and an interior cavity cooperatively defined by the interior proximal wall, the interior distal wall, the first interior lateral wall, and the second interior lateral wall, the first exterior lateral wall being at least partially disposed on a plane that is outwardly directed at a first exterior angle (ψ1) with respect to a first outer plane on which the lower surface is at least partially disposed, extending from the lower surface, the first interior lateral wall being at least partially disposed on a plane that is outwardly directed at a first interior outward angle (θ1) with respect to the first outer plane, extending from the lower surface to the upper surface; the first exterior lateral wall defining a first chamfered portion and a first groove , the second exterior lateral wall defining a second chamfered portion and a second groove , the first exterior lateral wall being at least partially disposed on a plane that is outwardly directed at a first connecting angle (κ1) with respect to the first outer plane, extending from the lower surface to the first chamfered portion. an exterior proximal wall , an exterior distal wall , a first exterior lateral wall , a second exterior lateral wall , an upper surface , a lower surface , a first interior lateral wall extending from the upper surface to the lower surface, a second interior lateral wall extending from the upper surface to the lower surface, an interior proximal wall extending from the upper surface to the lower surface and adjacent the first interior lateral wall and the second interior lateral wall, an interior distal wall extending from the upper surface to the lower surface and adjacent the first interior lateral wall and the second interior lateral wall, a longitudinal axis extending through planes containing the upper surface and the lower surface and through a geometric centre of the main body, and an interior cavity cooperatively defined by the interior proximal wall, the interior distal wall, the first interior lateral wall, and the second interior lateral wall, the first exterior lateral wall being at least partially disposed on a plane that is outwardly directed at a first exterior angle (ψ1) with respect to a first outer plane on which the lower surface is at least partially disposed, extending from the lower surface, the first interior lateral wall being at least partially disposed on a plane that is outwardly directed at a first interior outward angle (θ1) with respect to the first outer plane, extending from the lower surface to the upper surface; the first exterior lateral wall defining a first chamfered portion and a first groove , the second exterior lateral wall defining a second chamfered portion and a second groove , the first exterior lateral wall being at least partially disposed on a plane that is outwardly directed at a first connecting angle (κ1) with respect to the first outer plane, extending from the lower surface to the first chamfered portion. <EOS>