Anterior cervical pedicle screw

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Cervical fixation

General

• Strongest fixation in anterior cervical reconstruction.

• This technique is not a replacement for common cervical spine surgeries but rather a technical adjunct for selected cases.

Indications:

• Where biomechanical stability of conventional anterior cervical spine screw and plate systems is limited because:
• Fusion and complication rates in anterior cervical spine surgery correlate directly with mechanical stability.
• Long strut grafts or cages used for reconstruction are biomechanically inferior and vulnerable to failure, often requiring revision.
• There is a high rate of non-union (20–50%) in multilevel Anterior Cervical Discectomy and Fusion (ACDF) or a high failure rate (30–100%) for long-length decompression or corpectomies.

• Need to avoid posterior instrumentation or external bracing (halo)
• Added risks and duration of surgery
• Patient discomfort associated with halo vests.

• Multilevel (4-5 levels) anterior decompression and reconstruction for anterior pathologies in the cervical spine:
• Cervical spondylotic myelopathy and/or radiculopathy.
• Posterior longitudinal ligament ossification.
• Post-traumatic kyphosis.

• Selected cases that demand anterior reconstruction despite severe osteoporosis.

• Revision after conventional plate fixation failure, with C2 levels given as an example.

Technique

• Patient Positioning and Preparation
• Supine position.
• Neck is slightly extended, and the head is fixed with tape.
• Surgical level of the cervical spine is positioned as parallel to the floor as possible to facilitate fluoroscope handling.
• Shoulder girdles are pulled caudally and immobilised by tape.
• Pedicle axis view at the surgical level is confirmed preoperatively.

• Surgical Exposure, Decompression, and Grafting
• The anterior surgical site is exposed, typically one level above and one level below the decompression lesion, through a left oblique incision.
• Following exposure, subtotal corpectomy and decompression are performed.
• Strut grafting is then carried out using either iliac bone or fibula.

• Cervical Pedicle Screw Insertion
• A multiplanar fluoroscope is initially set on the patient's left side to obtain an accurate lateral view of the cervical spine.
• The fluoroscope is then rotated (with the axis of rotation set to a cervical longitudinal axis) until it depicts the approximate circular portion of the pedicle cortex in the transverse plane of the vertebral body, known as the pedicle axis view.
• This view is particularly helpful in lower cervical spine cases where shoulders may obscure good lateral views, as it indicates the pedicle entry point.

• The pedicle axis is usually inclined at 35°–50° from the mid-sagittal plane for C3–7.
• The authors specifically used a screw trajectory angle of 45° for C3–6 and 40° for C7.
• The centre of the cortical circular area visualised with the image intensifier indicates the insertion point of the screw on the vertebral body
• An entry hole is created with a straight awl, typically about 2 mm below the upper end and central to the transverse plane.
• A 1.4 mm guidewire of a cannulated screw is inserted into the pedicle cavity using a drill, maintaining a 45° inclination from the sagittal plane, which conforms to the C-arm beam angle of the fluoroscope.
• The placement of guidewires is confirmed repeatedly using AP, lateral, and pedicle axis views via fluoroscopy
• If a guidewire migrates outside the pedicle, insertion is reattempted to establish the correct pathway.
• After inserting guidewires at each level, tapping is performed.

• Plate Fixation
• The precise length of the anterior plates (axis plate) is selected and bent to conform to the contour of the physiological lordosis
• The diameter of the cannulated (pedicle) screws is 4 mm, and their length typically ranges from 30 to 34 mm.

Images

• Preoperative and postoperative imaging studies of the illustrative case of C6/C7 bilateral dislocation.

• (A-D) Preoperative computed tomography (CT) images showing the C6/C7 right (B) and left (C) facet joint dislocation.

• (E-F) Preoperative (E) and postoperative (F) T2 sagittal magnetic resonance images showing C6/C7 spinal cord compression and decompression.

• (G) Post- operative anteroposterior and lateral radiograph showing the reduction and fixation of anterior pedicle screws and plate.

• (H) Six months’ postoperative sagittal CT images showing C6/C7 fusion and sagittal alignment.

• (I) Six months’ postoperative 3-dimensional CT reconstruction image showing right facet fusion after facetectomy.

• (J-K) Postoperative axial CT images demonstrating good placement of anterior pedicle screws and vertebra screws at C6 (J) and C7 (K).a