Medical devices suitable for implantation in spaces between bones are described. An example medical device suitable for use as an intervertebral spacer includes a main body having an exterior proximal wall, an exterior distal wall, a first exterior lateral wall, a second exterior lateral wall, an upper surface, a lower surface, an interior proximal wall, an interior distal wall, a first interior lateral wall, a second interior lateral wall, and a longitudinal axis. The interior proximal wall, the interior distal wall, the first interior lateral wall, and the second interior lateral wall cooperatively define an interior cavity. The first and second exterior lateral walls are outwardly directed at an angle from the lower surface to the upper surface relative to the longitudinal axis.