Spontaneous interbody fusion after controlled injuries to the spine: an experimental study in rabbits

To evaluate the rationale of spontaneous spine fusion after a spinal injury, the authors conducted an experimental study that consisted of three types of controlled injuries to a rabbit spine model. The first was injury to the intervertebral disk (type I injury). The second was injury of the intervertebral disk along with injury to one of the adjacent vertebral end plates (type II). In type III injury, both the opposing end plates were injured along with the intervertebral disk. In 38 rabbits, a total of 82 injuries of these three types were inflicted. Twenty-six injuries were of type I (n = 22 rabbits), 26 were type II (n = 24 rabbits), and 30 were type III (n = 26 rabbits). Spontaneous fusion occurred only in type III injuries. From the 30 type III injuries, fusion occurred in 20 (66.6%). For an autofusion to occur, both epiphyseal plates may be injured. In the clinical situation, this observation suggests that a radiographically obscure lesion of both neighboring vertebrae may proceed to autofusion of that spinal segment observed later.