Spinal instrumentation refers to different types of devices and implants used during spine surgery. When spinal instrumentation is used during spine surgery, the goal is to stabilize the spine in order to prevent motion while fusion occurs between two or more vertebrae. Bone graft is commonly used in instrumented surgical procedures to stabilize the spine and enhance fusion. Some types of graft help stimulate new bone growth which is essential for a successful fusion.
Types of instrumentation can include pedicle screws, rods, connectors, plates, and interbody cages.
The pedicle is a tube of bone that connects to the back of a vertebral body and extends out posteriorly. Each vertebral body has two pedicles that help form the ring of bone around the spinal cord. Pedicle screws anchor into the pedicles to hold rods and connectors in place. A rod fits into the pedicle screw heads on either side of the spine, connecting vertebrae and preventing movement. Horizontal connectors (similar to cross-bracing) attach to the rods to further stabilize the construct.
Pedicle screw constructs can be used in the lumbar spine (lower back) to help fuse one or more vertebral levels to treat conditions such as herniated disc, degenerative disc disease, spondylolisthesis, and trauma. Longer constructs can extend up to the thoracic (mid-back) and even cervical (neck) spine to treat scoliosis, kyphosis, and other spinal deformities.
Note: In the thoracic spine, pedicle hooks are often used instead of screws because the thoracic pedicles are small and present difficult angles.
Once fusion takes place, the pedicle screw construct no longer serves a purpose. Usually by then, bone has grown around the screws, making a second surgery for removal difficult and unnecessary unless an implant breaks or some other difficulty occurs.
Metal plates are usually used in anterior cervical fusion (front of the neck) surgery to stabilize the vertebrae during fusion and to hold graft material in place. Newer cervical plate designs allow slight movement and settling of the bone graft. It is theorized that these new plates improve the probability for successful fusion.
In lumbar interbody fusion, plates are sometimes used on the front or side of the vertebral body. Small screws hold the plates in place.
Interbody cages are implants to help restore disc height and provide a space that can be filled with bone graft material. Interbody means between two intervertebral bodies. Interbody devices can be used in the cervical and lumbar spine. These devices help limit movement and assist with stabilizing the spine as fusion occurs.
The earliest cage designs were metal thimble- or cylinder-shaped cages with threads that allowed them to be screwed into place in the front of the vertebrae. Two cages were filled with graft material and placed side-by-side.
Cages have evolved to include different shapes and sizes that allow them to be inserted between the intervertebral bodies from the anterior (front), posterior (rear), and side (lateral). They can be made of metal, plastic, carbon fiber, and donor bone. In making a decision about which type of cage or interbody device to use, your surgeon considers the level to be treated, number of levels and amount of weight the cage must bear.
Spinal instrumentation is frequently combined. Of course, this decision depends on the patient's disorder, health and size, as well as many other considerations. Common combinations include an interbody cage with a pedicle screw construct, or an interbody cage with an anterior plate.
Deciding what type of instrumentation to use is based on your surgeon's recommendation. Considerations include the spinal level(s) to be surgically treated, bone graft options, and weight-bearing demands of the level(s).
Spine surgery is an important decision. While the final decision is yours to make, the benefits and potentials risks and complications require careful consideration. We look forward to answering your questions and helping you to resolve your concerns about any treatment offered by Piedmont Spine Center.