Intervertebral cage

1. An intervertebral cage insertable between vertebrae of a spine comprising:

a main body defined by a pair of upper and lower surfaces and a pair of side surfaces connected thereto; and

a withdrawal prevention portion formed on the upper and/or the lower surfaces of the main body,

wherein the withdrawal prevention portion regulates an insertion direction of the intervertebral cage,

wherein the main body is formed in a hollow body and is made thicker on a rear side in the direction of insertion than on a front side,

wherein the withdrawal prevention portion comprises a plurality of claw portions whose cutting lines are formed in a direction nearly perpendicular to a bisector line nearly bisecting an angle formed by a side surface and a front surface of the main body,

and wherein a screw through hole is formed to pass through surfaces which form a V-shaped groove in a sectional side view in a rear end surface of the main body and are opposed to each other.

2. The intervertebral cage according to claim 1 , wherein the screw through hole is an elongated hole made in a direction perpendicular to a longitudinal direction of the intervertebral cage.

3. The intervertebral cage according to claim 1 , wherein the direction of insertion is regulated in a direction perpendicular to the cutting lines.

4. The intervertebral cage according to claim 1 , wherein the main body has a vertical through hole passing through the upper and lower surfaces, a transverse through hole passing through the side surfaces from one side to the other side, and a hole formed from a front end surface in a direction of insertion of the main body to a rear end surface opposite to the front end surface.