1. Field of the Invention
The present invention relates to an artificial intervertebral disc (i.e., a movable vertebral body spacer) which can be implanted in a portion of a removed intervertebral disc to surgically treat a hernia of the intervertebral disc, or an injury of a cervical vertebra or the like.
2. Description of Related Art
A herniated intervertebral disc causes a patient to feel a severe pain due to the spinal nerves being pressed by a central nucleus pulposus, which is deviated by regressive change in the intervertebral disc. There are several kinds of hernias of intervertebral discs, most of which are those of the lumbar part. There is also a hernia of the intervertebral disc of the neck, which is caused by an external wound resulting from a fall, a traffic accident, or the like. It is also known that a hernia can be suddenly caused at night or at day time.
A hernia of an intervertebral disc, if relatively slight, can be treated by fixing the intervertebral disc, but if it is serious, a surgical operation is necessary. In conventional surgical treatments (i.e., operations), after the injured intervertebral disc is removed, a bone is implanted between upper and lower vertebral bodies. In the bone implantation, either a part of the iliac bone of the patient, or an artificial bone made of alumina or apatite, is used. In these methods, however, the vertebral bodies which are naturally movable per se are immovably fixed and, accordingly, the vertebral bodies can not move relative to each other.
There has been a long need for the development of a movable biomaterial which is implanted between vertebral bodies.