C1-C2 Posterior Fusion (Harms/Goel-Harms Technique)

Indication. Symptomatic atlantoaxial (C1-C2) instability that has failed or is unsuitable for non-operative care, demonstrated by an abnormal ADI (greater than 3 mm in adults, greater than 5 mm in children), cord compression, or a clearly unstable injury. The common pathologies are: - Traumatic: Type II odontoid fracture non-union (after 6 months of failed healing, or in the elderly with poor bone quality unsuitable for an anterior odontoid screw), Type III odontoid fracture with C2 body comminution, irreducible atlantoaxial rotatory subluxation, transverse ligament rupture (ADI greater than 5 mm indicates ligament incompetence), and Jefferson (C1 burst) fracture with transverse ligament disruption and instability.

• Rheumatoid arthritis: pannus erosion of the odontoid or transverse ligament with an ADI greater than 9 mm (cord compression risk), basilar invagination from bone erosion, and atlantoaxial subluxation with myelopathy.
• Congenital: os odontoideum with instability (a separate ossicle detached from the C2 body), Down syndrome atlantoaxial instability from ligamentous laxity (ADI greater than 5 mm), and Morquio syndrome (mucopolysaccharidosis).
• Degenerative / other: atlantoaxial osteoarthritis with instability (rare), chronic irreducible rotatory subluxation, tumour destroying C1-C2 (primary or metastatic) requiring reconstruction, and infectious instability such as Grisel syndrome in children. Contraindications. Absolute: an irreducible atlantoaxial dislocation (needs anterior transoral odontoidectomy or occiput-C2 fusion first), severe osteoporosis preventing screw purchase (T-score less than -4.0), and active infection at C1-C2 until treated. Relative: a C2 pedicle less than 3 mm wide (use translaminar screws), a vertebral artery anomaly precluding safe pedicle screws (use translaminar), a previous failed C1-C2 fusion requiring revision, or a young patient who cannot accept the loss of 50% of cervical rotation. The one decision that matters — which C2 screw. Every Harms-Goel fusion begins with the same C1 lateral mass screws; the real choice is the C2 fixation, dictated by the preoperative CT:

Consent specifically for the permanent loss of about 50% of cervical rotation (difficulty driving, checking blind spots, and rotation sports), likely occipital numbness if the C2 nerve is sacrificed, a 1-2% risk of an airway-threatening haematoma, a 2-4% vertebral artery injury risk with a small chance of posterior circulation stroke, and 8-12 weeks in a hard collar. Setup. Prone on a radiolucent Jackson table or chest rolls with Mayfield 3-pin head fixation. Biplanar fluoroscopy and SSEP/MEP neuromonitoring are essential throughout. Plan 150 minutes of anaesthetic time.

The goal is to stabilise a reducible atlantoaxial instability by placing independent C1 lateral mass and C2 pedicle screws, link them with rods, compress across the C1-C2 facets, decorticate and graft those facets, and confirm reduction on imaging — all while protecting the vertebral artery, the spinal cord and the venous plexus. The exposure and screw trajectories below are the heart of the operation.

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Rehabilitation | Phase | Timing | Immobilisation | Activity | |-------|--------|----------------|----------| | 1 | 0-24 h | Hard collar on in theatre; ICU airway monitoring | Bed to chair day 1 if neurologically intact | | 2 | Days 1-7 | Hard collar 24/7 | Ambulate day 1-2 with therapy; soft diet (10-20% transient dysphagia); DVT prophylaxis; discharge day 2-4 | | 3 | Weeks 2-6 | Hard collar 24/7 | Remove staples week 2; upright lateral X-ray in collar at week 6 | | 4 | Weeks 8-12 | Wean collar if flexion-extension films stable | Desk work from 6-8 weeks (possible in collar) | | 5 | Months 6-12 | Off collar once CT confirms fusion | Driving after collar off and fusion stable; heavy labour after CT fusion | A hard collar (Philadelphia or Miami-J) is worn continuously for 8-12 weeks — longer than subaxial fusions (typically 6 weeks) because the biomechanical stress at C1-C2 is high. Driving is not allowed in a collar and only resumes once the collar is discontinued and the fusion is stable; counsel the patient about the permanent 50% rotation loss (they must adjust mirrors and turn the whole body to check blind spots). Contact sports are generally discontinued permanently. About 80-85% achieve good-to-excellent pain relief when instability was the pain source (Grob 1992). Complications

Historical evolution. Atlantoaxial fixation has progressed through four generations. Gallie wiring (1939) passed a sublaminar wire under the C1 arch and over the C2 spinous process with graft between — a posterior tension band giving flexion stability only, with 85-90% fusion and a 3-month halo. Brooks wiring (1978) added bilateral sublaminar wires for better rotational control but similar fusion. Magerl transarticular screws (1987) crossed the C1-C2 facet into the C1 lateral mass with excellent biomechanics, but the vertebral artery overlies the trajectory in 18-20%, so bilateral screws cannot be placed safely in 20%, and perfect reduction is required before screw insertion. The Harms technique (2001) — C1 lateral mass plus C2 pedicle screws linked by rods — became the gold standard because it allows reduction after screw insertion, is safer for the vertebral artery, and is feasible in 98% of patients. Goel (1994) described the same segmental construct independently and earlier; the two are now called the Harms-Goel technique. Why it works: pathoanatomy. The atlas is a ring without a vertebral body; its lateral masses (15-20 mm thick at the arch junction) are the screw target, and the vertebral artery runs in a groove on the superior surface of the posterior arch only 2-3 mm lateral to that target. The axis carries the odontoid; its pedicle (pars/isthmus — the same structure) is a narrow 4-8 mm corridor between the spinal canal medially and the transverse foramen laterally. The transverse atlantal ligament (TAL) is the prime C1-C2 stabiliser — its rupture or an odontoid fracture allows anterior C1-on-C2 translation, measured by the ADI (normal less than 3 mm adults, less than 5 mm children; greater than 5 mm means TAL incompetence; greater than 9 mm in rheumatoid disease risks cord compression). Fusing C1-C2 sacrifices the 40-50° of rotation each way that the C1-C2 articulation contributes — half of all cervical rotation — while preserving occiput-C1 motion (15° flexion-extension, 5° rotation).

Fusion rates and biomechanics. In the pooled Elliott meta-analysis (2012), screw-rod constructs fused in about 97% (97.4% with bracing versus 97.9% without — no significant benefit from a postoperative collar), against 94-95% for transarticular screws. The Harms construct reduces flexion-extension motion by 95% and rotation by 88% (Melcher 2002; Gorek 2005), versus 65%/55% for Gallie wiring. Intraoperative fluoroscopy materially under-detects vertebral artery violations: Yeom (2008) found 21% of C2 pedicle screws caused vertebral artery groove violations on postoperative CT and one C1 screw caused arterial occlusion — none detected intraoperatively or on plain films — which is why a low threshold for postoperative CT is advised. Vertebral artery anatomy is the whole game. Anomalies are common and significantly more so in atlantoaxial instability: a high-riding vertebral artery (present in about 20% of CT scans, and narrowing the mean C2 pedicle width to only 2.53 mm versus 5.83 mm in controls, Kothari 2019), fenestration (2-3%), a persistent first intersegmental artery (1-2%), and a dominant vertebral artery (10%). Byun (2022) confirmed these anomalies are significantly more frequent in patients with atlantoaxial instability, with a correspondingly narrower C2 safe zone — reinforcing the rule of a mandatory preoperative CT angiogram before any screw-rod fixation.