The spine or vertebral column comprises a plurality of separate vertebrae. The vertebrae are movable relative to one another, and separated from one another by fibrocartilage called inter-vertebral discs.
In its entirety, the spinal column is highly complex in that it houses and protects critical elements of the nervous system which have innumerable peripheral nerves and arterial and venous bodies in close proximity. In spite of these complexities, the spine is a highly flexible structure, capable of a high degree of curvature and twist through a wide range of motion. The intervertebral discs provide mechanical cushion between adjacent vertebrae. Genetic or developmental irregularities, trauma, chronic stress, tumors, and disease, however, can result in spinal pathologies which either limit this range of motion, or which threaten the critical elements of the nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve immobilization by implanting artificial assemblies in or on the spinal column.
In order to treat certain injuries or conditions of the spinal column an intervertebral device may be placed in the intervertebral disc space to fuse or promote fusion of adjacent vertebrae. Such fusion devices are often used in combination with stabilisation systems wherein a metal rod that is bendable to match the natural curvature of the spine is mechanically attached at strategically selected vertebrae, allowing the rod to be rigidly fixed to the spine. This provides a rigid support to the spinal column. For this, pedicle screws located in the bone structure are typically fixed to a specially designed clamp to attach to a spinal rod. A problem with these stabilisation systems is that parts of the vertebra cannot stably receive a bone screw, or can only receive a bone screw screwed in at a certain angle. Also, for spinal fixings for small animals, within the confined spaces allowed therein, conventional rod anchoring methods are not suitable since the placement of the pedicle screw and the direction of the rod cannot be matched adequately. A system that can be used in small animals is needed, wherein confined spaces make conventional rod anchoring systems unsuitable. Furthermore, many devices for providing positioning of bone screws with respect to a stabilising rod loosen over time, providing an unstable joint. There is therefore a need for a solution that overcomes one or more of these problems.