The spinal column is a bio-mechanical structure composed primarily of ligaments, muscles, bones, and connective tissue that forms a series of vertebral bodies stacked one atop the other and intervertebral discs between each vertebral body. The spinal column provides support to the body and provides for the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs; complex physiological motion between these parts; and protection of the spinal cord and the nerve roots.
Common spinal column disorders include degenerative disc disease, facet arthritis, and other conditions such as spondylolysis, spondylolisthesis, scoliosis, fractured vertebra, ruptured or slipped discs, tumors, or infections and other disorders caused by abnormalities, disease or trauma. Patients who suffer from one of more of these conditions often experience extreme pain, and can sustain permanent neurologic damage if the conditions are not treated appropriately.
The stabilization of the vertebra and the treatment for above described conditions is often aided by a surgically implanted fixation device which holds the vertebral bodies in proper alignment and reduces the patient's pain and prevents neurologic loss of function. Spinal fixation is a well-known and frequently used medical procedure. Spinal fixation systems are often surgically implanted into a patient to aid in the stabilization of a damaged spine or to aid in the correction of other spinal deformities. Existing systems often use a combination of rods, plates, pedicle screws, bone hooks locking screw assemblies and connectors for fixing the system to the affected vertebrae. The system components may be rigidly locked together in a variety of configurations to promote fusion for a wide variety of patient anatomies.
Posterior fusion and fixation may be the optimal approach for patients in whom the construct requires an extension to the upper cervical or thoracic spine, and to the occiput. Overall, posterior stabilization is generally preferred for posterior and circumferential cervical injuries. Several kinds of posterior fixation systems have been devised. Examples include sublaminar wiring with rod/plate fixation, laminar hook with rod fixation, and pedicle screw with a rod fixation system. However, the sublaminar wiring system has a restriction because the lower cervical laminae are smaller and weaker than upper thoracic vertebrae; and, laminar hooks are not preferred because they cannot be fixed in the narrow spinal canal. Alternatively, posterior screw fixation systems provide excellent stability and strength for patients without any external support.
Advancements in posterior cervical fixation have progressed from a wiring procedure to hook and plate-screw systems; and more recently to the versatile rod-screw system.
In some fixation systems, the plates are mounted to the skull with several small screws along the full length and width of the plate. As a result, the spinal rods must be bent in multiple planes away from the vertebrae in order to reach the occipital region. This bending of the rod may potentially weaken the overall assembly, and result in longer operations; and also makes it more difficult to reposition the elements of the stabilization system.
Therefore, there is a need for a posterior cervical fixation system that includes the easy installation of rods which would reduce the risk of implant failure and loss of alignment; and provide for easy adaptation for extension to the occiput or cervical/thoracic spine.