The spinal column is a highly complex system of bones and connective tissues that provides support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one atop the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces experienced by the spinal column. A vertebral canal containing the spinal cord and nerves is located behind the vertebral bodies.
There are many types of spinal column disorders including scoliosis (abnormal lateral curvature of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnormal backward curvature of the spine, usually in the lumbar spine), spondylolisthesis (forward displacement of one vertebra over another, usually in a lumbar or cervical spine) and other disorders caused by abnormalities, disease or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like. Patients that suffer from such conditions usually experience extreme and debilitating pain, as well as diminished nerve function.
An exemplary spinal treatment for some of the above problems involves a technique known as spinal fixation. In spinal fixation, surgical implants are used for fusing together and/or mechanically immobilizing vertebrae of the spine. Spinal fixation may also be used to alter the alignment of adjacent vertebrae relative to one another so as to change the overall alignment of the spine. The spine may be immobilized by using orthopedic rods, commonly referred to as spine rods, that run generally parallel to the spine. This may be accomplished by exposing the spine posteriorly and fastening bone screws to the pedicles of the appropriate vertebrae. The pedicle screws are generally placed two per vertebra and serve as anchor points for the spine rods. Clamping elements adapted for receiving a spine rod therethrough are then used to join the spine rods to the screws. The aligning influence of the rods forces the spine to conform to a more desirable shape. In certain instances, the spine rods may be bent to achieve the desired curvature of the spinal column.
A number of apparatuses, sometimes referred to as jig assemblies, are used to adjust the position and orientation of the vertebra and their respective spine rods prior to setting the spine rod in the desired final position. Known jig assemblies are typically connected to the pedicle screws and around the rod in order to adjust the position of the rod and vertebra. During the adjustment process, the rod is firmly engaged against the pedicle screws so that the screws and vertebra move in an articulating relationship with the positional adjustment of the rod. Most jigs have one or more components that can lock the rod in a fixed position. Once the adjustment procedure is completed and the rod is set in a desired position, the rod is tightened against the pedicle screws to fix the screws and their respective vertebra in the desired position. To facilitate access to the rod for tightening, the typical jig assembly must be removed from the screws. This has the disadvantage of leaving the rod temporarily unsecured and unrestrained, potentially allowing the rod and vertebra to shift out of the set position. In addition, this methodology requires a number of steps, including the step of removing the jig from the screws prior to tightening the rod. Therefore, known jig assemblies have certain characteristics that may be undesirable for spinal reduction procedures.