The transpedicular approach is a specific surgical technique in spine procedures, translating literally to “across the pedicle.” This approach is fundamental to modern spinal fixation because it allows surgeons to anchor instrumentation directly into the strongest part of the vertebral column. It is a method of access, primarily used to place screw-like implants deep into the vertebral body for stabilization. The transpedicular technique provides three-column spinal stability, addressing issues from the front, middle, and back of the spine through a single posterior incision.
Understanding the Spinal Pedicle
The pedicles are two short, thick segments of bone that extend backward from the vertebral body, acting as a bridge to the posterior bony arch of the vertebra. They are dense, cylindrical structures that enclose the spinal canal, which houses the spinal cord and nerve roots. This composition of compact bone makes the pedicle the structurally robust component of the vertebra, capable of withstanding significant mechanical stress.
The pedicle’s unique location makes it the ideal anchor point for spinal instrumentation, especially pedicle screws. This bone transfers mechanical loads between the weight-bearing anterior vertebral body and the posterior elements, like the facet joints and lamina. Understanding the precise dimensions and angulation of each pedicle is important, as these characteristics vary significantly across different levels of the spine.
Primary Use in Spinal Stabilization
The transpedicular approach is predominantly used for spinal stabilization, achieved through the placement of pedicle screws. These screws act as fixed points connected by rods, creating a rigid internal brace to hold two or more vertebrae together. This construct is the basis of spinal fusion, a procedure designed to stop motion between unstable vertebral segments. Fusion is necessary to treat instability caused by degenerative disc disease, spinal deformity like scoliosis, or spondylolisthesis, where one vertebra slips over another.
The technique is also employed to stabilize severe vertebral fractures, particularly burst fractures where bone fragments push into the spinal canal. In trauma cases, the transpedicular approach is used for fixation and posterior decompression. By carefully drilling through the pedicle, surgeons access the vertebral body from behind to remove bone fragments compressing the spinal cord. This provides the necessary stability for healing while allowing for internal reduction of the fracture.
Guiding the Transpedicular Trajectory
The success of the transpedicular approach hinges on accurately determining the specific entry point and trajectory for each screw. The entry point on the back of the spine is typically found at the intersection of a vertical line along the lateral edge of the superior facet and a horizontal line through the transverse process. Once the outer layer of bone is breached, specialized instruments create a channel, or pilot hole, that follows the natural anatomical path of the pedicle.
The trajectory, or angle, of the screw must be carefully planned because the pedicle angles inward toward the center of the vertebral body. This transverse angle increases from the upper lumbar region to the lower lumbar spine, where it can reach nearly 30 degrees. To ensure a safe and precise path, advanced imaging guidance is frequently used, including real-time fluoroscopy, which provides a live X-ray view during the procedure. Sophisticated systems, such as CT navigation and robotic assistance, rely on pre-operative scans to map the exact three-dimensional route, increasing the accuracy of screw placement.
Safety and Risk Factors
The primary safety consideration in the transpedicular approach is the close proximity of the spinal cord and nerve roots to the placement site. The pedicle forms the boundaries of the narrow passage that contains the delicate neural structures. A slight deviation in the screw’s trajectory can lead to malpositioning, where the implant breaches the bone wall of the pedicle.
Unrecognized screw misplacement is a risk that can result in direct irritation or injury to the nerve root or spinal cord. This injury may cause symptoms such as new or worsening pain, numbness, or motor weakness in the limbs. A small percentage of patients may experience transient or permanent nerve root injury attributable to the screw’s position. Furthermore, a misplaced screw compromises the fixation strength, potentially leading to construct failure and inadequate spinal stabilization.