Advancements in the posterial fixation with axial isthmus screws / 中华骨科杂志

ABSTRACT

Axial pedicle screw fixation technique, as a classic posterior fixation technique, is the first choice and gold standard of posterior axial screw fixation. Since it can pass through the whole vertebrae and play the role of three-column fixation, it has excellent biomechanical properties and is widely used in cervical spine surgery. However, with the deepening of clinical research, some scholars found that the application of axial pedicle screws was limited in patients with pedicle hypoplasia, high-riding vertebral artery and irreducible atlantoaxial dislocation. At the same time, in order to expose bone markers during screw placement, the muscle dissection of pedicle screws is wider compared with that of isthmus screws. Isthmus screw fixation, as a complementary technique for pedicle screw technique, has gradually attracted the attention of scholars in recent years and has been applied in the surgical treatment of various types of cervical spine diseases. The entry point of axial isthmus screw is closer to the midline of the spine and the inferior facet joint than pedicle screw, to avoid extensive muscle dissection during the operation, so that the paravertebral muscles can be protected, which make the surgery more minimally invasive and the invasion of the operation further reduced. At the same time, compared with the lateral mass or pedicle screw of the atlas combined with axial pedicle screw fixation, the lateral mass or pedicle screw of the atlas combined with axial isthmus screw fixation can increase the anteroposterior and vertical distance between the heads of C 1 and C 2 screws due to the change of screw entry points, which can provide a wider operative space for the three dimensional reduction of atlantoaxial dislocation. However, since the axis is a transitional vertebra between the upper and lower cervical spine which has complexity and variability in anatomical structure, many scholars have limited understanding of this new technique. There are no unified standards for screw placement and surgical details, which are mostly based on the personal experience of clinicians. Meanwhile, the biomechanical properties, surgical complications and long-term efficacy of this technique have received little attention and concern, resulting in the limitation of clinical application and promotion for this technique. This review evaluates the relative advantages of axial isthmus screws according to existing literature reports, and analyzes the anatomy, biomechanics, clinical applications and surgical complications of axial isthmus screw fixation technique, aiming to provide a reference for the safety and feasibility of axial isthmus screw placement.