Literally this means a false joint. It is another term that describes what happens when a bone does not fuse properly following some spinal surgeries. It is also called a "non-union," or failure to fuse, and can be painful. It sometimes requires revision surgery in order to make a solid fusion.

lack or failure of fusion.

A form of non-union in which there is the formation of a false joint with some cartilage covering the ends of the bones and a cavity containing fluid that resembles a normal joint.