Occipito-Cervical Stabilization Using Occipital Condyle Screw

Overview

The Occipito-Cervical (OC) junction is the most cephalad portion of the spinal axis, with anatomical osseous complex that allows significant mobility while maintaining biomechanical stability. OC instability is a rare disorder with potentially life-threatening consequences. Instability may manifest as disabling pain, cranial nerve dysfunction, paralysis, or even sudden death. The most common acute presentation is secondary to major trauma. Other pathologic processes that may lead to chronic instability include rheumatoid arthritis, infections, tumors, and even congenital malformations; OC fusion in aforementioned cases each according is then indicated. Stabilization of the OC junction remains a challenge, owing to the regional anatomy and poor occipital bone purchase. OC stabilization techniques have undergone continuous refinement. Early techniques involving simple posterior only bone grafts demonstrated a high rate of failure and have largely been replaced by rigid posterior fixation systems using rods/screws or plates, providing superior biomechanical stability and higher rates of fusion. One of the very modern modalities of fixation methods is the Occipital Condyle Screw (OCS) as a sole cranial anchor; believing that decreasing the length of lever arm of the construct, increasing the length of the screw purchase, and decreasing stresses addressed on the rod with no need to excessively bend it for the occipital slope may enhance the construct rigidity, and leaving a greater clear metal-free area of the occiput for graft contact may have a real potential benefits in fusion rates.

Clinical Evaluation: of patients with 1- Visual Analogue Scale (VAS), 2- Neck Disability Index (NDI), 3- Modified Japanese Orthopaedic Association Cervical Myelopathy Score (mJOA.CMS), 4- American Spinal Injury Association Score (ASIAs). Immediate preoperative functional scoring, and 6 weeks, 3 months, 6 months, and 1 year postoperative. Surgical Technique: The patient is handled in prone position after successful general anaesthesia with supported head to ensure that the Occipito-Cervical junction maintains in neutral position. The Occipito-Cervical junction is then exposed through a traditional midline longitudinal posterior skin incision extends from the external occipital protuberance to the C3-C4 level. The nuchal ligament is divided in the midline, and the occipital and cervical musculature is dissected subperiosteally. The suboccipital and cervical paraspinous muscles are retracted laterally to expose the underlying bony architecture. The posterior arch of C1 is exposed and the dissection is continued laterally in a subperiosteal manner to identify the horizontal segment of the vertebral arteries (VAs) which is enveloped in a dense venous plexus. The atlanto-occipital joint capsule is to be approx. 3 mm. Cranial to the superior margin of tht VA. Attention is then focused on the foramen magnum. Using curettes, the atlanto-occipital membrane is gently dissected from the foramen magnum laterally until the medial aspect of the occipital condyle is reached. At this point, the dissection continues laterally, maintaining bone contact to prevent injury to the horizontal segment of the VA along the condylar fossa, until the posterior condylar foramen and emissary vein are identified. The condylar foramen and vein represent the lateral extent of the dissection. At this stage, the operative field is prepared for instrumentation. Inserting the cervical screws first provides useful information about the axial location of the occipital condyles. The condylar entry point (CEP) is defined using a combination of radiographic and anatomic landmarks. The CEP is located (4 to 5 mm) lateral to the posteromedial edge of the condyle, and (2 mm) above the atlanto-occipital joint line. Pilot hole is then made at the entry point using an awl with slight cranial angulation to avoid injury to the horizontal segment of the VA. The pilot hole is then drilled under image-guidance in a convergent trajectory with (12 to 22 degrees) of medial angulation and (5 degrees) cranial angulation in the sagittal plane with the tip of the drill directed toward the basion, advancing slowly until the anterior cortical edge of the condyle is breached. The hole is tapped, and a (3.5 mm) polyaxial screw of an appropriate length (30 to 34 mm) is inserted bicortically into the occipital condyle. Approximately (12 mm) portion of the screw remains superficial to the posterior cortex of the condyle, allowing the polyaxial portion of the screw to lie above the posterior arch of C1, minimizing any chance of irritation of the VA by the rods. Radiological Evaluation: 1- Preoperative: Plain X-ray (PXR) Antero-posterior (AP) and Lateral (Lat.) views to study the upper cervical instability indices and measurements, Multi-Slice Computed Tomography (MSCT) to study the boney Occipito-Cervical architecture for any fractures or anomalies, CT Angiography (CTA) to study the vertebral artery for anomaly especially in the horizontal segment of the VA, and Magnetic Resonance Imaging (MRI) to study the spinal cord for any compression signs. 2- Postoperative: Immediate (PXR) AP. and Lat. views for overall global assessment of the reduction and the construct installation. Then at 3 months, 6 months, and 1 year after surgery with flexion extension lateral view bending stress films for assessment of stability. Immediate (MSCT) to study the crucial screws placement estate for any breaches or successfulness, and after 1year for assessment of the fusion rate achieved. Serial Follow-Up: after 6 weeks for clinical evaluation and functional scoring. At 3 and 6 months for radiological evaluation of stability, clinical evaluation and functional re-scoring. At 1 year for evaluation of fusion rate, clinical evaluation and over all resultant functional scores.