What is the entry point in the dorsal and lumbar spine for spine fixation surgery?

From the Guidelines

The entry point for pedicle screw placement in spine fixation surgery differs between the dorsal (thoracic) and lumbar spine, with the thoracic spine entry point typically at the junction of the lateral third and medial two-thirds of the transverse process and facet joint, and the lumbar spine entry point generally at the junction of the transverse process, pars interarticularis, and the mamillary process. In the context of spine fixation surgery, the choice of entry point is critical to avoid damaging nearby neural structures. The provided evidence 1 discusses various surgical approaches, including posterior, lateral, and posterolateral approaches, but does not specifically address the entry points for pedicle screw placement in the dorsal and lumbar spine. However, based on general medical knowledge and the importance of avoiding neural structure damage, the following anatomical landmarks are typically used to guide surgeons:

• Thoracic spine: junction of the lateral third and medial two-thirds of the transverse process and facet joint, slightly inferior to the superior facet
• Lumbar spine: junction of the transverse process, pars interarticularis, and the mamillary process, slightly lateral and inferior to the facet joint The trajectory for screw insertion also varies:
• Thoracic pedicle screws are typically directed more medially (0-10 degrees)
• Lumbar screws are directed more laterally (10-15 degrees medially) The sagittal trajectory should follow the angle of the superior endplate. Preoperative imaging, including CT scans, helps determine the appropriate screw size and trajectory based on individual patient anatomy 1. It is essential to note that the evidence provided does not directly address the question, but based on the available information and general medical knowledge, the recommended entry points and trajectories can help minimize the risk of complications and improve patient outcomes.

From the Research

Entry Point in Dorsal and Lumbar Spine

• The entry point for dorsal and lumbar spine fixation surgery is crucial for the success of the procedure 2.
• A keyhole approach for endoscopically assisted pedicle screw fixation in lumbar spine instability has been developed, which reduces surgical traumatization and destabilization of adjacent motion segments 2.
• The screw entry point into the pedicles is localized by endoscopic dissection of the mamilloaccessory ligament, bridging the mamilloaccessory notch 2.
• Alternative posterior fixation techniques, such as cortical bone trajectory (CBT) screws, transfacet screws, and translaminar screws, have been developed to reduce surgical time, soft-tissue dissection, and neurologic risk 3, 4.
• These alternative techniques may be preferred in certain lumbar degenerative cases, particularly among patients with osteoporosis 4.
• Pedicle screw fixation is the preferred method of posterior fusion in lumbar spinal surgery, providing three-column support of the vertebrae 3.
• The technique of pedicle screw fixation involves the insertion of screws into the pedicles of the vertebrae, which requires precise localization of the screw entry point 2, 5.
• The use of pedicle screw fixation in traumatic fractures of the thoracic and lumbar spine has been studied, and the results suggest that it is a effective method of treatment 5.
• However, the choice of pedicle screw fixation technique depends on various factors, including the type of fracture, the patient's condition, and the surgeon's preference 5, 6.

Surgical Techniques

• The surgical technique for posterior lumbar fusion involves the insertion of cages or grafts between vertebrae to achieve solid bone fusion 6.
• Instrumentation methods, such as pedicle screw placement, require meticulous preparation to ensure safe insertion and optimal outcomes 6.
• The use of alternative posterior fixation techniques, such as CBT screws and transfacet screws, may reduce the risk of complications and improve patient outcomes 4.
• The choice of surgical technique depends on the individual patient's needs and the surgeon's expertise 6.

Safety Considerations

• The safety of pedicle screw fixation depends on precise localization of the screw entry point and careful insertion of the screws 2, 5.
• The use of alternative posterior fixation techniques may reduce the risk of complications, such as neurologic injury and implant failure 4.
• The surgeon's experience and expertise are crucial factors in ensuring the safety and success of the procedure 6.