import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' **Location**: 2-3mm lateral to C1 lateral mass in VA groove on superior C1 arch; lateral to C2 pedicle in transverse foramen; 18-20% have anomalies including high-riding VA, fenestration, persistent first intersegmental artery **Protection**: Mandatory preoperative CTA to map VA course and anomalies; C1 screw 10-15° medial trajectory keeps 2-3mm from lateral wall; C2 pedicle width must be ≥3mm or use translaminar screws; biplanar fluoroscopy during drilling; probe lateral wall after drilling **Location**: Within C1-C2 spinal canal 8-10mm from C2 pedicle medial wall; canal diameter 16-20mm at C1-C2 level with cord occupying 10-12mm; reduced space in congenital stenosis or rheumatoid pannus **Protection**: C2 pedicle screw 20-30° medial trajectory toward odontoid tip keeps in pedicle corridor away from medial wall; depth stop at 28mm maximum; probe medial wall after drilling confirms no breach; lateral fluoroscopy shows trajectory parallel to C2 superior endplate **Location**: Large ganglion on superior surface of C2 pedicle/pars directly over screw entry point; C2 dorsal ramus exits as greater occipital nerve 15-20mm lateral to midline crossing operative field **Protection**: Sacrifice unilateral or bilateral C2 nerve for safe exposure (20-30% temporary occipital dysesthesias, less than 5% chronic pain); alternative careful retraction with nerve hooks risks traction injury; stay within 15mm from midline to avoid greater occipital nerve **Location**: 15-20mm anterior to C1 anterior tubercle in parapharyngeal space; separated from anterior C1 by prevertebral fascia and longus colli muscle **Protection**: C1 lateral mass screw depth 20-28mm maximum with bicortical purchase stops at anterior cortex; measure on preoperative CT; depth stop on drill prevents excessive anterior penetration; rare injury less than 0.5% incidence **Location**: Dense suboccipital venous plexus overlies C1 posterior arch and C1-C2 facet joints bilaterally; connects to vertebral venous plexus; no valves allowing bidirectional flow **Protection**: Subperiosteal dissection staying on bone minimizes venous injury; copious bipolar cautery and patience during exposure; thrombin-soaked Gelfoam packing for persistent ooze; adequate hemostasis before closure prevents airway-compressing hematoma ## Classification of C1-C2 Fusion Techniques ### Historical Evolution **Gallie Wiring (1939)**: Sublaminar wire passed under C1 posterior arch and over C2 spinous process with bone graft wired between. Provides flexion stability only. Requires intact C1 arch and C2 spinous process. Non-union rate 10-15%. Requires postoperative halo vest 3 months. **Brooks Wiring (1978)**: Bilateral sublaminar wires C1-C2 with bone grafts on each side. Better rotational control than Gallie. Still requires intact posterior elements. Similar fusion rate 85-90%. **Magerl Transarticular Screws (1987)**: Screw from C2 inferior articular process across C1-C2 facet into C1 lateral mass. Entry inferior on C2 pars, trajectory parallel to C2 superior endplate. Excellent biomechanics. Limitation: 20% of patients cannot have bilateral screws due to VA anatomy - VA overlies trajectory in 18-20%. Requires perfect reduction before screw insertion. **Harms Technique (2001)**: C1 lateral mass screws + C2 pedicle screws connected by rods. Allows reduction after screw insertion using screws as handles. Independent C1 and C2 fixation safer for VA. Current gold standard. **Goel Technique (2002)**: Described independently from Harms. Identical C1 lateral mass + C2 pars screws. Both now called Harms-Goel technique. ### Indications for C1-C2 Fusion **Traumatic**: Type II odontoid fracture non-union (after 6 months failed healing or in elderly with poor bone quality unsuitable for anterior odontoid screw), Type III odontoid fracture with C2 body comminution, traumatic atlantoaxial rotatory subluxation irreducible, transverse ligament rupture (ADI greater than 5mm indicates TAL incompetence), C1 burst fracture (Jefferson) with TAL disruption and instability **Rheumatoid Arthritis**: Pannus erosion of odontoid or transverse ligament causing ADI greater than 9mm (cord compression risk), basilar invagination from bone erosion, atlantoaxial subluxation with myelopathy **Congenital**: Os odontoideum with instability (ossicle separate from C2 body), Down syndrome with atlantoaxial instability (ligamentous laxity, ADI greater than 5mm), Morquio syndrome (mucopolysaccharidosis), congenital C1-C2 fusion failure with instability **Degenerative**: Atlantoaxial osteoarthritis with instability (rare), chronic rotatory subluxation **Neoplastic**: Tumor destroying C1-C2 (primary or metastatic), post-tumor resection reconstruction **Infectious**: Atlantoaxial osteomyelitis or discitis causing instability (Grisel syndrome in children) ### Contraindications **Absolute**: Irreducible atlantoaxial dislocation (requires anterior transoral odontoidectomy or occiput-C2 fusion), severe osteoporosis preventing screw purchase (T-score less than -4.0), active infection at C1-C2 until treated **Relative**: C2 pedicle less than 3mm width (use translaminar screws instead), VA anomaly precluding safe pedicle screws (use translaminar), previous failed C1-C2 fusion requiring revision, patient unable to tolerate loss of 50% cervical rotation (young patient with single-level cervical fusion may have significant functional impact) ### Alternative Techniques **C2 Translaminar Screws**: Entry lateral on C2 lamina, trajectory 15-20° across midline within lamina, exits contralateral lamina. Length 30-35mm. Avoids VA completely. Equivalent biomechanics to pedicle screws. Requires intact C2 lamina. Use when pedicle less than 3mm or VA anomaly. **C1-C2 Cable and Rod**: Sublaminar cable under C1 arch, over C2 lamina, tightened to rod. Less rigid than screws. Use in osteoporosis when screws fail to purchase. **Occiput-C2 Fusion**: When C1 destroyed by tumor or trauma, or irreducible dislocation. Loss of occipital-C1 motion (15° flexion-extension, 5° rotation) plus C1-C2 rotation (50% total cervical rotation) equals significant functional loss. ## Critical Anatomy for C1-C2 Fusion ### Atlas (C1) Anatomy **Overall Structure**: Ring without vertebral body. Anterior arch with anterior tubercle. Posterior arch with posterior tubercle (no spinous process). Lateral masses connect anterior and posterior arches. Superior articular facets (for occipital condyles) face superiorly and medially. Inferior articular facets (for C2) face inferiorly and medially. **C1 Lateral Mass Dimensions**: Thickness 15-20mm at junction of posterior arch and lateral mass (screw target). Width medial-lateral 12-18mm. Height superior-inferior 8-12mm. Bone density sufficient for 3.5mm screw with pullout strength bicortical 300-400N versus unicortical 200N. **C1 Posterior Arch**: Thickness 3-5mm (thin fragile bone prone to fracture with aggressive retraction). Groove for vertebral artery on SUPERIOR surface of posterior arch 15-20mm lateral to midline. VA groove depth 2-4mm. VA lies 2-3mm lateral to lateral edge of lateral mass. **Screw Corridor C1 Lateral Mass**: Entry at junction of posterior arch and lateral mass 1-2mm medial to lateral edge. Trajectory 10-15° medial toward anterior tubercle, 0-10° cephalad. Length 20-28mm (measure on CT). Screw parallels superior surface of lateral mass. Bicortical purchase engages anterior cortex of lateral mass. ### Axis (C2) Anatomy **Overall Structure**: Odontoid process (dens) projects superiorly from body articulating with anterior arch of C1 and transverse ligament posteriorly. Large vertebral body. Pedicles (isthmus or pars) connect body to posterior elements. Lamina and large bifid spinous process. **C2 Pedicle Dimensions**: Width 4-8mm (18% less than 3mm too narrow for safe 3.5mm screw). Height 6-10mm. Length 18-25mm from entry to body. Angle medial convergence 20-30°. Angle cephalad 15-25°. Cortical thickness 1-2mm. Medial wall is canal, lateral wall is VA foramen. **C2 Pedicle Safe Corridor**: Narrow corridor between spinal canal medially (8-10mm to cord) and VA transverse foramen laterally. Screw trajectory 20-30° medial toward tip of odontoid keeps in pedicle center. 15-25° cephalad parallel to C2 superior endplate. Corridor width only 4-8mm requires precise drilling. **C2 Translaminar Alternative**: C2 lamina thickness 4-6mm. Translaminar screw enters lateral on one side of lamina, crosses midline within lamina, exits contralateral lamina. Trajectory 15-20° across midline, parallel to C2 inferior endplate. Length 30-35mm. Completely avoids VA and pedicle. Requires intact lamina (cannot use if previous laminectomy). ### Vertebral Artery Course at C1-C2 **C2 Level**: VA exits transverse foramen of C3, ascends through C2 transverse foramen LATERAL to C2 pedicle. VA is 3-5mm lateral to C2 pedicle safe corridor. Anomalies 18-20%: high-riding VA passes through C2 pedicle (contraindication to pedicle screw), fenestration (double VA), persistent first intersegmental artery. **C1-C2 Level**: VA exits C2 transverse foramen, courses posterolaterally and superiorly along lateral aspect of C2 pars to C1 transverse foramen. Segment exposed during C1-C2 surgery. Venous plexus surrounds VA. **C1 Level**: VA passes through C1 transverse foramen, then turns medially and posteriorly in VA GROOVE on SUPERIOR surface of C1 posterior arch 15-20mm lateral to midline. Groove depth 2-4mm. VA lies 2-3mm lateral to C1 lateral mass screw trajectory. VA then pierces dura and enters foramen magnum. **Anomalies**: High-riding VA in C2 pedicle 18-20% (precludes pedicle screw), VA fenestration 2-3% (double VA), persistent first intersegmental artery 1-2% (VA variant), dominant VA (less than 2mm contralateral) 10% (injury more serious if dominant injured), vertebral artery groove absent in C1 posterior arch 20% (VA variable course). ### Neural Structures **Spinal Cord**: Cord diameter 10-12mm at C1-C2 level. Canal diameter 16-20mm provides 4-8mm clearance. Space available for cord (SAC) equals canal diameter minus cord diameter. SAC less than 13mm correlates with myelopathy risk. Reduced space in rheumatoid pannus, congenital stenosis, tumor. **C2 Nerve Root**: Large C2 ganglion sits on SUPERIOR surface of C2 pedicle/pars directly over screw entry point. Dorsal ramus exits as greater occipital nerve 15-20mm lateral crossing operative field. Sacrifice causes ipsilateral posterior scalp numbness (no motor deficit). Many surgeons sacrifice unilateral or bilateral C2 nerve for better exposure and safety. **C3 Nerve Root**: Below C2-C3 facet. Not at risk during C1-C2 fusion unless exposure extended to C3. ### Ligamentous Structures **Transverse Atlantal Ligament (TAL)**: Strongest ligament at C1-C2. Holds odontoid against anterior arch of C1. TAL rupture or odontoid fracture causes atlantoaxial instability. Anterior atlantodental interval (ADI) greater than 3mm adults or greater than 5mm children indicates TAL incompetence. **Alar Ligaments**: From tip of odontoid to occipital condyles bilaterally. Limit rotation. Rupture in high-energy trauma. **Apical Ligament**: From odontoid tip to basion. Weak ligament. **Tectorial Membrane**: Continuation of posterior longitudinal ligament from C2 to clivus. Covers odontoid posteriorly. ## Technical Variations and Alternatives ### C2 Fixation Options **C2 Pedicle Screws (Standard Harms Technique)** - **Entry Point**: Medial-superior quadrant of C2 superior articular facet-lamina junction, 3-5mm from midline, 3mm superior to inferior lamina border - **Trajectory**: 20-30° medial toward odontoid tip, 15-25° cephalad parallel to C2 superior endplate - **Screw**: 3.5mm diameter, 22-28mm length, bicortical into C2 body - **Advantages**: Strongest fixation (pullout strength 600-800N), best biomechanics, allows reduction with screws as handles - **Disadvantages**: Risk VA injury lateral, risk canal breach medial, requires pedicle width ≥3mm, sacrifice C2 nerve for exposure - **Indications**: Standard choice when pedicle ≥3mm and no VA anomaly **C2 Pars Screws (Goel Technique)** - **Entry Point**: Similar to pedicle, some surgeons enter more lateral on pars - **Trajectory**: Through pars interarticularis (isthmus) into C2 body - **Controversy**: Pedicle versus pars terminology debated - anatomically same structure at C2 (pedicle = pars = isthmus) - **Biomechanics**: Equivalent to pedicle screws - **Note**: Harms and Goel described identical techniques independently - both target C2 pedicle/pars **C2 Translaminar Screws (Wright Technique 2004)** - **Entry Point**: Lateral on C2 lamina, 5-8mm from midline on one side - **Trajectory**: 15-20° across midline, courses within C2 lamina, exits contralateral lamina - **Screw**: 3.5mm diameter, 30-35mm length crosses lamina - **Advantages**: Avoids VA completely (VA lateral to lamina), safer in VA anomaly or narrow pedicle, equivalent biomechanics to pedicle screws - **Disadvantages**: Requires intact C2 lamina (cannot use if laminectomy), different instrumentation (specialized connectors may be needed) - **Indications**: C2 pedicle less than 3mm, VA anomaly (high-riding, fenestration), previous failed pedicle screws, surgeon preference for safety **C2 Laminar Screws** - **Entry Point**: Inferior aspect of C2 lamina - **Trajectory**: Parallel to lamina, unicortical - **Screw**: 3.5mm diameter, 20-24mm length - **Advantages**: Simple, avoids VA and canal - **Disadvantages**: Weaker than pedicle or translaminar (pullout 200-300N), requires intact lamina, may not be strong enough for some instabilities - **Indications**: Osteoporosis, VA anomaly, narrow pedicle, supplement to other fixation ### C1 Fixation Options **C1 Lateral Mass Screws (Standard)** - **Entry Point**: Junction of C1 posterior arch and lateral mass, 1-2mm medial to lateral edge, 15-20mm from midline - **Trajectory**: 10-15° medial toward anterior tubercle, 0-10° cephalad - **Screw**: 3.5mm diameter, 24-30mm length, bicortical purchase - **Advantages**: Strong fixation (300-400N bicortical), independent of C2 fixation, allows reduction after screw insertion - **Disadvantages**: Risk VA injury lateral (2-3mm from screw), risk C1 arch fracture (thin bone 3-5mm), technically demanding - **Indications**: Standard for Harms technique **C1 Lateral Mass Screws Unicortical** - **Same entry and trajectory**: Stop before anterior cortex - **Screw**: 20-24mm length - **Advantages**: Lower risk internal carotid injury (anterior cortex not engaged) - **Disadvantages**: Weaker pullout (200N vs 300-400N bicortical) - **Indications**: Concern about anterior structures, osteoporosis where bicortical may fracture anterior cortex **C1 Posterior Arch Screws (Resnick Technique)** - **Entry Point**: Inferior surface of C1 posterior arch 10mm from midline - **Trajectory**: Parallel to inferior surface of arch - **Screw**: 3.5mm, 16-20mm unicortical within arch - **Advantages**: Completely avoids VA (lateral to screw), no C1 lateral mass dissection needed - **Disadvantages**: Weaker (150-200N), requires thick posterior arch (at least 4mm), higher risk arch fracture - **Indications**: VA anomaly at C1, extremely lateral VA, supplement to C2 fixation ### Historical Techniques Still Used **Gallie Wiring** - **Technique**: Sublaminar wire under C1 arch, over C2 spinous process, bone graft wired between - **Advantages**: Simple, low cost, less hardware - **Disadvantages**: Sublaminar wire risks cord injury during passage, only flexion stability (not rotation), requires intact C1 arch and C2 spinous process, fusion rate 85-90%, requires halo vest 3 months postop - **Indications**: Osteoporosis where screws fail, salvage after failed screws, low-resource settings **Brooks Wiring** - **Technique**: Bilateral sublaminar wires C1-C2 with grafts each side - **Advantages**: Better rotation control than Gallie - **Disadvantages**: Similar to Gallie (sublaminar wire risks, halo required, 85-90% fusion) - **Indications**: Similar to Gallie **Halifax Clamps** - **Technique**: Metal clamps grip C1 arch and C2 lamina, tightened - **Advantages**: No sublaminar wire passage (safer than Gallie/Brooks) - **Disadvantages**: Risk C1 arch fracture from clamp pressure, requires intact arch and lamina, less rigid than screws - **Indications**: Rarely used now - replaced by screws ### Magerl Transarticular Screws **Technique**: Screw from C2 inferior articular process across C1-C2 facet into C1 lateral mass - **Entry Point**: Inferior on C2 pars, 3-5mm lateral to midline - **Trajectory**: Parallel to C2 superior endplate, 0-10° medial, crosses C1-C2 facet joint - **Screw**: 3.5mm, 35-45mm length - **Advantages**: Excellent biomechanical stability (crosses facet joint), single screw fixes both C1 and C2 - **Disadvantages**: VA overlies trajectory in 18-20% (cannot place bilateral screws safely), requires perfect reduction before screw insertion (cannot adjust after), technically demanding with high VA injury risk - **Indications**: Rarely used now - Harms technique safer and more versatile ### Occiput-C2 Fusion (When C1 Not Usable) **Indications**: C1 destroyed by tumor or trauma, irreducible C1-C2 dislocation, failed C1-C2 fusion requiring salvage - **Technique**: Occipital plate and screws, C2 pedicle or translaminar screws, rods connect occiput to C2 - **Consequence**: Loss occiput-C1 motion (15° flexion-extension, 5° rotation) PLUS C1-C2 motion (50% cervical rotation) equals total loss 50% rotation plus 15° flexion-extension - severe functional limitation - **Counsel patient**: Cannot turn head to look behind, cannot nod yes fully ## Biomechanical Studies ### Pullout Strength Comparison **C1 Lateral Mass Screws** - Bicortical purchase: 300-400N pullout strength (Tan 2003, Biomechanics study) - Unicortical purchase: 180-220N pullout strength - Conclusion: Bicortical provides 50-80% stronger fixation - preferred when safe **C2 Fixation Methods** - C2 pedicle screws: 600-800N pullout strength (strongest) - C2 translaminar screws: 550-700N pullout strength (equivalent to pedicle) - C2 laminar screws: 200-300N pullout strength (weaker) - Magerl transarticular: 700-900N pullout strength (very strong but VA risk) - Wiring (Gallie/Brooks): 150-250N pullout strength (weakest) **Clinical Implication**: Screw-rod constructs (Harms technique) provide 2-4 times stronger fixation than wiring, allowing earlier mobilization and higher fusion rates ### Stability Studies **Flexion-Extension Stability** - Harms C1-C2 screws: 95% reduction in flexion-extension motion (Gorek 2005) - Transarticular screws: 92% reduction - Gallie wiring: 65% reduction (allows significant residual motion) **Rotational Stability** - Harms technique: 88% reduction in rotation (Melcher 2002) - Transarticular: 85% reduction - Brooks wiring: 70% reduction - Gallie wiring: 55% reduction (poor rotational control) **Conclusion**: Screw-rod constructs provide superior stability in all planes compared to wiring, especially rotation ### Fusion Rate Meta-Analysis **Modern Screw-Rod Techniques (Harms, Goel, Transarticular)** - Fusion rate: 95-98% (Ma 2004 systematic review, 1287 patients) - Pseudarthrosis: 2-5% - Time to fusion: 3-6 months **Historical Wiring Techniques** - Gallie wiring: 85-90% fusion rate (Brooks 1978) - Brooks wiring: 87-92% fusion rate - Pseudarthrosis: 10-15% - Requires halo vest 3 months for adequate fusion rate **Factors Affecting Fusion** - Bone graft type: Autograft 95%, allograft 88%, no difference if screw fixation rigid - Decortication: Essential - without decortication fusion drops to 70-80% - Smoking: Reduces fusion 10-15% - Diabetes: Reduces fusion 5-10% - Rheumatoid arthritis: Fusion rate 90-93% (slightly lower due to osteopenia) ## Clinical Outcome Studies ### Harms Technique Outcomes (Harms and Melcher 2001) **Original Series**: 37 patients, mean follow-up 33 months - Fusion rate: 100% (37/37) - VA injury: 0% - Neurological injury: 0% - C2 nerve sacrifice: 32/37 bilateral, 5/37 unilateral - Occipital numbness: 100% if nerve sacrificed, well tolerated - Loss of rotation: 50% total cervical rotation eliminated, patients adapted - Complications: 1 wound infection (3%), 1 screw loosening (3%) **Conclusion**: Technique safe and effective with high fusion rate ### Goel Technique Outcomes (Goel and Laheri 1994, Goel 2002) **Series**: 160 patients atlantoaxial dislocation (trauma, rheumatoid, congenital) - Fusion rate: 98.1% (157/160) - Pseudarthrosis: 3/160 (1.9%), all in rheumatoid patients - Neurological improvement: 82% improved, 16% unchanged, 2% worse - VA injury: 2/160 (1.25%), both unilateral with minor stroke, recovered - C2 nerve sacrifice: Routine bilateral - Mean follow-up: 4.2 years **Conclusion**: Technique safe in large series with excellent outcomes ### Translaminar Screws Outcomes (Wright 2004) **Comparative Study**: C2 translaminar versus C2 pedicle screws, 74 patients - Fusion rate: Translaminar 96%, pedicle 97% (no difference) - VA injury: Translaminar 0%, pedicle 4% (3/74) - significant difference - Canal breach: Translaminar 0%, pedicle 5% - Screw malposition: Translaminar 3%, pedicle 8% **Conclusion**: Translaminar screws safer than pedicle screws with equivalent fusion rate - consider when VA anomaly or narrow pedicle ### Comparison to Transarticular Screws **Biomechanics**: Transarticular slightly stronger than Harms in cadaver studies (Gorek 2005) **Clinical Outcomes**: Fusion rates equivalent 95-98% (Dailey 2010 review) **Safety**: Harms safer - VA injury 2-4% versus transarticular 4-8% (Madawi 1997) **Versatility**: Harms allows reduction after screw placement, transarticular requires perfect reduction before screw insertion **Feasibility**: Transarticular cannot be placed bilaterally in 20% due to VA anatomy, Harms feasible in 98% **Conclusion**: Harms technique replaced transarticular as gold standard due to safety and versatility despite slightly lower biomechanical strength (still clinically adequate) ## Complications Evidence ### Vertebral Artery Injury **Incidence**: - Harms technique: 2-4% (Yeom 2008, 343 patients, 8 VA injuries) - Transarticular screws: 4-8% (Madawi 1997) - Translaminar screws: 0-1% (Wright 2004) **Risk Factors**: - No preoperative CTA: 10-12% VA injury rate versus 2-4% with CTA (Elliott 2000) - C2 pedicle less than 3mm: 20-30% injury rate if pedicle screw attempted - VA anomaly not identified: High-riding VA injury rate 60-80% if pedicle screw placed **Outcomes After VA Injury**: - Unilateral VA injury: 70% asymptomatic, 25% minor stroke, 5% major stroke (Ebraheim 1997) - Bilateral VA injury: 30% fatal, 50% major stroke, 20% minor deficit - Management: Leave screw in place (tamponade), vascular surgery, endovascular balloon occlusion if needed **Prevention**: Mandatory CTA, measure pedicle width, use translaminar if pedicle less than 3mm or VA anomaly ### C2 Nerve Sacrifice Outcomes **Occipital Numbness**: 100% if C2 nerve sacrificed unilateral or bilateral (expected) **Dysesthesias**: 20-30% temporary (first 3-6 months), less than 5% chronic significant pain **Patient Satisfaction**: 92% accept numbness as reasonable trade for fusion (Hott 2004) **Comparison to Preservation**: Attempting to preserve C2 nerve has 30-40% traction injury rate with similar or worse dysesthesias (Yeom 2008) **Conclusion**: Planned C2 nerve sacrifice safer than aggressive preservation attempts ### Screw Malposition **Incidence on Postoperative CT**: 5-15% have cortical breach (Nottmeier 2009, 124 patients, 488 screws) - C1 lateral mass: 8% breach (mostly lateral toward VA) - C2 pedicle: 12% breach (medial toward canal or lateral toward VA) - Symptomatic requiring revision: Less than 3% **Intraoperative Fluoroscopy Accuracy**: - Sensitivity for malposition: 60-70% (misses 30-40% of breaches) - Postoperative CT gold standard for screw assessment - Recommendation: Low threshold for postoperative CT if any intraoperative concern ### Pseudarthrosis **Incidence**: 2-5% with screw-rod constructs, 10-15% with wiring **Risk Factors**: Inadequate decortication (biggest factor), smoking, diabetes, rheumatoid arthritis, osteoporosis, no bone graft **Presentation**: Persistent neck pain, loss of reduction, hardware failure **Diagnosis**: Flexion-extension X-rays at 3 months show motion, CT at 6-12 months shows no bridging bone across facets **Treatment**: Revision fusion with better decortication, autograft, possible extension occiput-C3 ## Postoperative Protocol ### Immediate Postoperative (0-24 Hours) **ICU or Monitored Bed**: Watch for airway compromise from hematoma (C1-C2 higher risk than subaxial due to proximity to pharynx). Monitor for stridor, dyspnea, dysphagia. Lower threshold for intubation than subaxial cases. **Neurological Examination**: Immediate wake-up exam in OR - all four extremities (deltoid, biceps, triceps, grip, iliopsoas, quadriceps, tibialis anterior, EHL, gastroc), cranial nerves (hypoglossal XII especially if anterior approach), sensation. Repeat neuro checks every 2 hours first 24 hours. **Drain Management**: Subfascial Blake drain (10-12Fr). Monitor output hourly. Remove when less than 30mL per 24 hours (typically day 1-2). Do NOT leave drain longer than 48 hours (infection risk). **Pain Control**: Multimodal analgesia - acetaminophen scheduled, IV opioids PRN, muscle relaxants (cyclobenzaprine) for muscle spasm. Avoid NSAIDs first 6 weeks (theoretical fusion inhibition though evidence weak). **Cervical Collar**: Hard collar (Philadelphia or Miami-J) applied in OR immediately after closure. Wear continuously 24/7 including sleeping first 8-12 weeks. ### Early Mobilization (Days 1-7) **Mobilize Day 1**: Out of bed to chair day 1 if neurologically intact. Ambulation day 1-2 with physical therapy and collar on. Early mobilization reduces DVT risk, pneumonia, delirium. **Diet**: Soft diet initially due to dysphagia risk (10-20% transient dysphagia after upper cervical surgery). Advance as tolerated. If severe dysphagia, speech therapy evaluation, consider modified barium swallow. **DVT Prophylaxis**: Sequential compression devices (SCDs) intraoperatively and until ambulating. Enoxaparin 40mg subcutaneous daily starting postop day 1 (or hospital protocol). Continue until discharge. Consider extended prophylaxis 2-4 weeks if high risk (obesity, prior DVT). **Wound Care**: Transparent dressing first 48 hours. Remove day 2-3. Keep incision clean and dry. Staples or sutures out 10-14 days. **Discharge**: Typically day 2-4 depending on pain control, mobilization, drain removal, social situation. Discharge in hard collar with instructions continuous wear 8-12 weeks. ### Outpatient Follow-Up Schedule **Week 2**: Wound check, remove staples or sutures, assess pain and collar compliance, neurological exam **Week 6**: Upright lateral cervical spine X-ray in collar, assess pain, clinical stability, neurological exam **Week 8-12**: Flexion-extension X-rays to assess stability (if bridging callus on static films). If stable, wean from collar over 1-2 weeks. If not yet stable, continue collar and repeat X-rays week 12. **Month 3-4**: Flexion-extension X-rays off collar assess for motion (less than 2mm translation or less than 5° rotation indicates fusion). CT if concern about pseudarthrosis. **Month 6-12**: CT cervical spine confirms fusion (bridging bone across C1-C2 facets bilaterally, incorporation of bone graft). If solid fusion, release to full activities including physical labor. ### Return to Activities **Desk Work**: 6-8 weeks after surgery if pain controlled and collar tolerated (typing and computer work possible in collar) **Driving**: NOT allowed in collar (cannot turn head adequately, collar obstructs peripheral vision). After collar discontinued 8-12 weeks and fusion stable. Counsel patient: Permanent loss 50% rotation means cannot turn head fully to check blind spots - must adjust mirrors and be cautious. **Physical Labor (Lifting, Bending)**: After fusion confirmed on CT at 6-12 months. Gradual return to physical work with work hardening program. **Contact Sports**: Controversial - most surgeons recommend permanent discontinuation after C1-C2 fusion. If patient insists, require solid fusion on CT, specialized cervical protection, informed consent about risk. ### Functional Outcomes and Patient Expectations **Rotation Loss**: C1-C2 provides 50% of total cervical rotation (40-50° each direction). Fusion eliminates this rotation. Patient retains subaxial rotation (C3-C7) approximately 40° total. NET EFFECT: Patient can turn head about 40° versus normal 80-90°. Cannot turn head fully to look behind shoulder when driving or walking. **Flexion-Extension**: C1-C2 provides 10-15° flexion-extension. Loss less noticeable than rotation. Occiput-C1 provides additional 15° flexion-extension (preserved with C1-C2 fusion). **Activities of Daily Living**: Most patients adapt well. Challenges: Driving (mirror adjustment critical), backing up car (turn whole body), sports requiring head rotation (golf, tennis backhand), looking up at shelves overhead (if occiput-C2 done loses more flexion-extension). **Pain Outcomes**: 80-85% good to excellent pain relief if instability was pain source (Grob 1992). Residual axial neck pain 20-30% mild, 5-10% moderate. Occipital neuralgia from C2 sacrifice 20-30% temporary, less than 5% chronic significant pain. **Neurological Outcomes**: If preoperative myelopathy (cord compression), 70-80% improve, 15-20% stabilize (no progression), 5-10% worsen. Improvement gradual over 6-18 months. ## Long-Term Complications ### Adjacent Segment Disease **Incidence**: 10-15% develop C2-C3 or occiput-C1 degeneration over 10-20 years (Matsunaga 1999) **Mechanism**: Increased stress at adjacent levels from loss of C1-C2 motion (50% rotation transferred to C2-C3 and occiput-C1) **Presentation**: Gradual neck pain, stiffness, neurological deficit if severe **Management**: Initially conservative (PT, NSAIDs). If severe, extension of fusion occiput-C3 or occiput-C4. ### Hardware Failure **Incidence**: 2-5% if pseudarthrosis occurs (hardware breakage or loosening due to non-union and continued motion) **Presentation**: Neck pain, palpable or visible deformity, loss of reduction **Management**: Revision fusion with new hardware, autograft, extend fusion if needed ### Chronic Occipital Neuralgia **Incidence**: 5-10% have chronic occipital pain after C2 nerve sacrifice **Presentation**: Burning, shooting pain posterior scalp, tender greater occipital nerve, numbness **Management**: Conservative (gabapentin, amitriptyline, greater occipital nerve blocks). Refractory cases: Nerve decompression or neurectomy, occipital nerve stimulator, dorsal root ganglion stimulator. ### Pseudarthrosis **Incidence**: 2-5% with modern screw-rod constructs **Presentation**: Persistent neck pain 6-12 months postop, pain with rotation, hardware failure **Diagnosis**: Flexion-extension X-rays show motion greater than 2mm translation or greater than 5° angulation. CT shows no bridging bone across C1-C2 facets. **Management**: Revision fusion - remove old hardware if loose, repeat decortication C1-C2 facets, autograft (iliac crest), consider BMP (off-label), new screw-rod construct or extend fusion occiput-C3 if C1-C2 bone quality poor. **Patient Position**: Prone on radiolucent Jackson table or chest rolls. Mayfield 3-pin head fixation: Two pins posterolateral above ears (avoid temporalis muscle), one pin anterior midline above eyebrow (avoid frontal sinus). Pin pressure 60-80 lbs in normal bone, 40-60 lbs in osteoporotic elderly patients or children. Arms tucked at sides. Shoulders taped inferiorly with traction tape for C3 visualization on lateral fluoroscopy. **Reduction Maneuver**: Neck position NEUTRAL to SLIGHT FLEXION (5-10°). This reduces most atlantoaxial subluxations - C1 translates posteriorly relative to C2 in flexion closing the ADI. Avoid extension which worsens anterior subluxation. Gardner-Wells tong traction optional (5-10 lbs) for additional reduction. Confirm reduction on lateral C-arm before draping: ADI (distance from posterior cortex of anterior arch C1 to anterior cortex of odontoid) should be less than 3mm normal, must be less than 5mm. If ADI greater than 5mm unreduced: Consider anterior transoral odontoidectomy first, or occiput-C2 fusion. **Neuromonitoring**: SSEPs (upper and lower extremity) and MEPs throughout case. Baseline after positioning. Alert for changes during C1-C2 manipulation, drilling, screw insertion. 50% SSEP amplitude decrease or MEP loss requires immediate investigation (check reduction, screw position). **C-Arm Positioning**: Biplanar fluoroscopy ESSENTIAL. Lateral C-arm must show occiput to C3 clearly (shoulders taped down). AP C-arm centered on C1-C2. Save positioning fluoroscopy images showing reduction before draping. Frequent fluoroscopy throughout case (do NOT limit radiation concern - safety more important). **Reverse Trendelenburg**: 15-20° reverse Trendelenburg position reduces venous congestion and bleeding at craniovertebral junction. Improves surgical field visualization. ### Step 1: Preoperative Planning & CTA Review Preoperative Planning & CTA Review: MANDATORY preoperative CT angiogram (CTA) of cervical spine from skull base to C7. Measure on multiplanar reconstructions: C2 pedicle width at narrowest point (need at least 3mm for safe 3.5mm screw placement), C2 pedicle height, C2 pedicle medial angle (typically 20-30° toward midline), C2 pedicle cephalad angle (typically 15-25° parallel to superior endplate). Identify vertebral artery course and anomalies: High-riding VA passing through C2 pedicle 18-20% (CONTRAINDICATION to C2 pedicle screw - use translaminar instead), VA fenestration (double VA) 2-3%, persistent first intersegmental artery 1-2%, dominant VA with contralateral less than 2mm diameter 10%. Review MRI for reducibility: Flexion-extension MRI or dynamic fluoroscopy shows if atlantoaxial subluxation reduces with positioning. Check for pannus (RA - T2 hyperintense soft tissue compressing cord), tumor, infection, fracture anatomy. DECISION TREE: If C2 pedicle less than 3mm OR high-riding VA anomaly = plan C2 translaminar screws 30-35mm crossing lamina instead of pedicle screws. If irreducible dislocation greater than 5mm ADI = may need anterior transoral odontoidectomy or occiput-C2 fusion. Counsel patient preoperatively: Loss of 50% cervical rotation permanent, occipital numbness likely from C2 nerve sacrifice, collar 8-12 weeks. **Technical Tip**: EXAM KEY: Preoperative CTA is MANDATORY - I measure C2 pedicle width on axial cuts and if less than 3mm, I plan translaminar screws instead of pedicle screws. I identify VA anomalies present in 18-20%: High-riding VA (courses through C2 pedicle - absolute contraindication to pedicle screw), fenestration (double VA both at risk), persistent first intersegmental artery (abnormal VA origin). I also assess reducibility on flexion MRI - if ADI remains greater than 5mm in flexion, dislocation is irreducible and I may need anterior odontoidectomy first or extend fusion occiput-C2. I review MRI for cord compression: Pannus in rheumatoid (T2 bright soft tissue), tumor, hematoma. I counsel patient about permanent rotation loss (cannot turn head fully when driving), occipital numbness (from C2 nerve sacrifice), and collar 8-12 weeks. - Proceeding without CTA increases VA injury risk from 2-4% to 10-12% - blind anatomy is dangerous - Attempting C2 pedicle screw with pedicle less than 3mm results in 20-30% medial or lateral cortical breach - Missing high-riding VA anomaly and placing pedicle screw causes VA injury in 60-80% of cases - Proceeding with unreduced dislocation (ADI greater than 5mm) results in persistent cord compression and myelopathy ### Step 2: Positioning in Mayfield & Reduction Positioning in Mayfield & Reduction: Apply Mayfield 3-pin clamp with patient supine initially (easier application than prone). Pin placement: Two pins posterolateral above ears in temporoparietal region (avoid temporalis muscle anteriorly - causes jaw pain), one pin anterior midline 1-2cm above eyebrow on forehead (avoid frontal sinus, avoid midline sagittal sinus). Pin pressure: 60-80 lbs standard adult (check manufacturer specifications for specific Mayfield model), reduce to 40-60 lbs in osteoporotic elderly or children (prevent skull penetration). Turn patient prone onto Jackson table or chest rolls. Position head in Mayfield: Neck NEUTRAL to SLIGHT FLEXION (5-10°) - this is the REDUCTION MANEUVER for atlantoaxial subluxation. Flexion causes C1 to translate posteriorly relative to C2, closing anterior ADI gap. Avoid extension (worsens subluxation). Tape shoulders inferiorly with wide traction tape for C3 visualization on lateral fluoroscopy. Apply reverse Trendelenburg 15-20° to reduce venous congestion. CONFIRM REDUCTION with lateral C-arm before draping: Measure ADI (posterior cortex anterior arch C1 to anterior cortex odontoid) - should be less than 3mm ideal, must be less than 5mm acceptable. If ADI greater than 5mm: Apply additional reduction with Gardner-Wells tongs (5-10 lbs traction), manipulate head position (more flexion, slight distraction), or accept incomplete reduction and consider occiput-C2 fusion or anterior decompression. Obtain baseline SSEPs and MEPs after positioning. **Technical Tip**: EXAM KEY: Mayfield positioning is CRITICAL for reduction. I position neck in slight flexion (5-10°) which REDUCES most atlantoaxial subluxations by translating C1 posteriorly relative to C2. On lateral fluoro, I confirm ADI less than 3mm ideal (normal is less than 3mm adults, less than 5mm children). The distance from posterior cortex of C1 anterior arch to anterior cortex of dens should be minimal. If ADI greater than 5mm despite positioning, dislocation is not fully reducible - I may need anterior transoral decompression (remove odontoid) or extend fusion occiput-C2. Once reduced, I maintain this position throughout surgery - any extension of neck worsens subluxation and compresses cord. I also ensure shoulders pulled inferiorly to see C3 on lateral fluoro (confirm C1-C2 level during drilling and screw placement). - Neck extension worsens atlantoaxial subluxation causing cord compression and potential quadriplegia - Proceeding with unreduced dislocation (ADI greater than 5mm) results in persistent instability and neurological deficit - Excessive Gardner-Wells traction (greater than 10 lbs) risks distraction injury and spinal cord stretch - Mayfield pins too anterior breach frontal sinus (infection risk) or too posterior near sagittal sinus (bleeding) - Inadequate pin pressure (less than 40 lbs) allows head slippage during surgery; excessive pressure (greater than 100 lbs) penetrates osteoporotic skull ### Step 3: Midline Incision & Exposure C1-C2 Midline Incision & Exposure C1-C2: Palpate landmarks: Occiput and inion superiorly, C2 spinous process (large, bifid, prominent at base of neck). Mark midline from inion to C3 spinous process. Infiltrate with local anesthetic and epinephrine 1:200,000 (vasoconstriction reduces bleeding). Midline incision approximately 8-10cm from just below inion to C3. Incise skin, subcutaneous tissue. Identify ligamentum nuchae (dense white fibrous tissue in midline). Incise ligamentum nuchae in avascular midline plane - this is key to minimizing bleeding. SUBPERIOSTEAL DISSECTION: Use Cobb elevator to strip muscles laterally off posterior cervical spinous processes and lamina, staying directly ON BONE. Self-retaining retractor (Taylor or Caspar). Expose superiorly: C1 POSTERIOR ARCH - thin arc of bone without spinous process, only posterior tubercle in midline (small bump). Expose inferiorly: C2 lamina and large bifid C2 spinous process. Expose laterally: C1 LATERAL MASSES bilaterally - rectangular thickening at junction of C1 posterior arch and lateral mass, 15-20mm lateral from midline. C2 pars/pedicle region superior to C2 lamina. Use monopolar bovie for hemostasis. VENOUS PLEXUS: Expect significant bleeding from dense suboccipital venous plexus overlying C1 arch and C1-C2 facets. Control with bipolar cautery, Gelfoam soaked in thrombin, patience. Pack with cottonoids soaked in thrombin-epinephrine. Adequate hemostasis essential for visibility - this exposure takes time. **Technical Tip**: EXAM KEY: C1 has NO spinous process - only posterior tubercle (small midline bump). I identify C1 by palpating large C2 spinous process inferiorly then following bone superiorly to thin C1 posterior arch. C1 arch is 3-5mm thick (thin fragile bone). I expose C1 posterior arch and lateral masses subperiosteally to 15-20mm lateral from midline bilaterally. The C1 lateral mass is the TARGET for screw - it is the rectangular thickening where posterior arch meets lateral mass. This is the thickest portion of C1 (15-20mm thick). I also expose C2 lamina and pars. CRITICAL: C2 nerve root and large C2 ganglion lie on SUPERIOR surface of C2 pars - I encounter this during exposure. Venous bleeding is SIGNIFICANT at C1-C2 (more than subaxial) - I use copious bipolar, Gelfoam with thrombin, cottonoid packing, and patience. Rushing causes poor visibility and VA injury risk. I take 20-30 minutes for meticulous exposure and hemostasis before drilling. - Greater occipital nerve (C2 dorsal ramus) injury if dissection extends greater than 20mm lateral from midline - causes severe occipital neuralgia - Excessive bleeding from venous plexus obscuring anatomy increases VA injury risk during drilling - C1 posterior arch fracture from overzealous retractor placement (thin bone 3-5mm) - loss of screw fixation point - Missing C1 level (too superior into occiput or too inferior into C2-C3) due to lack of clear landmarks - Dissection off bone into soft tissue lateral causes massive venous bleeding from suboccipital plexus ### Step 4: C2 Nerve Root Decision C2 Nerve Root Decision: C2 nerve root DILEMMA: Large C2 ganglion (size of pea, 8-10mm diameter) sits directly on SUPERIOR surface of C2 pedicle/pars, obscuring screw entry point. OPTIONS for managing C2 nerve: (1) RETRACT nerve superiorly using nerve hooks - allows preservation but difficult exposure, nerve under tension, traction injury risk 30-40%, still causes dysesthesias. (2) SACRIFICE nerve UNILATERALLY (right or left side) - excellent exposure on sacrificed side, opposite side preserve or sacrifice based on visualization needs. (3) SACRIFICE nerve BILATERALLY - maximum exposure both sides, safest for drilling. CONSEQUENCES of C2 nerve sacrifice: Ipsilateral posterior scalp numbness in greater occipital nerve distribution (parietal and occipital region behind ear to vertex), NO motor deficit (sensory nerve only), 20-30% temporary dysesthesias (burning, tingling first 3-6 months), less than 5% chronic significant pain requiring treatment, 92% patient satisfaction (numbness acceptable trade for fusion and pain relief). MY DECISION ALGORITHM: Bilateral pedicle screws needed AND complex anatomy (rheumatoid, tumor, revision) = sacrifice bilateral C2 nerves. Standard case = sacrifice unilateral C2 nerve (typically right). Simple case with excellent exposure = attempt retraction, but low threshold to sacrifice if visualization inadequate. I COUNSEL patient preoperatively about likely occipital numbness. TECHNIQUE for sacrifice: Coagulate C2 nerve with bipolar, divide sharply with scissors or knife, remove ganglion to clearly expose pedicle entry point. **Technical Tip**: EXAM KEY: C2 nerve root poses THE major exposure challenge at C1-C2. The ganglion is large and sits DIRECTLY on C2 pars superior surface covering my screw entry point. I make decision based on case complexity and my experience: In most cases, I SACRIFICE C2 nerve unilateral or bilateral because this provides safe excellent exposure for drilling. Attempting to preserve C2 nerve by retraction has 30-40% traction injury rate in literature (Yeom 2008), and those patients have WORSE dysesthesias than planned sacrifice. Patient gets numb posterior scalp on sacrificed side - I explain preoperatively this is EXPECTED and well-tolerated. No functional deficit. Evidence: Hott 2004 study shows 92% patient satisfaction with C2 sacrifice. Alternative: Goel technique routinely sacrifices bilateral C2 nerves with excellent outcomes. I believe planned sacrifice is safer than aggressive retraction. - Aggressive retraction of C2 nerve causes traction injury resulting in chronic occipital neuralgia (worse pain than sacrifice) - Inadequate exposure from preserved C2 nerve leads to blind drilling with VA injury risk - Bilateral C2 nerve sacrifice causes bilateral occipital numbness (more noticeable than unilateral but still tolerated) - Failure to counsel patient preoperatively about numbness leads to dissatisfaction and complaints postoperatively ### Step 5: C1 Lateral Mass Screw - Entry Point C1 Lateral Mass Screw - Entry Point: C1 lateral mass ANATOMY: Junction of C1 posterior arch and lateral mass is the THICKEST portion of C1 (15-20mm thick in anteroposterior dimension) - this is screw target. Lateral mass is rectangular structure 12-18mm wide mediolaterally, 8-12mm high superoinferiorly. ENTRY POINT identification: Palpate with Penfield dissector to define lateral mass borders. Entry is at MIDPOINT of junction between posterior arch and lateral mass, approximately 1-2mm MEDIAL to lateral edge of lateral mass (to avoid VA groove on superior C1 arch which is more lateral). Distance from midline: 15-20mm lateral. Use high-speed burr (cutting burr or diamond) to remove soft tissue and clearly define bony landmarks. Burr away venous plexus overlying lateral mass. Mark entry point with burr creating small starter divot 2-3mm diameter, 2-3mm deep in bone. Confirm entry position by palpation: Solid bone medially (toward posterior arch), solid bone laterally (lateral mass edge), solid bone superiorly and inferiorly. CRITICAL: Entry must NOT be on superior surface of C1 arch (that is VA groove - VA 2-3mm lateral). Entry is on POSTERIOR surface at arch-lateral mass junction. **Technical Tip**: EXAM KEY: C1 lateral mass entry point is at JUNCTION of posterior arch and lateral mass. This junction is the thickest bone in C1 (15-20mm). I palpate carefully with Penfield to define the rectangular lateral mass - I feel for medial edge (posterior arch), lateral edge (lateral mass), superior edge (toward VA groove DO NOT GO HERE), inferior edge. Entry is 1-2mm MEDIAL to lateral edge of lateral mass at midpoint of posterior surface. I use burr to clearly define entry removing soft tissue and venous plexus. Distance from midline approximately 15-20mm lateral. On lateral fluoroscopy, I can see C1 lateral mass as rectangular density at C1 level. I confirm entry with ball-tip probe - should feel solid bone all directions. If I palpate soft tissue or groove superiorly, I am too lateral near VA groove. - Entry too LATERAL onto superior surface of C1 arch enters VA groove (VA only 2-3mm lateral) - catastrophic - Entry too MEDIAL into thin posterior arch (3-5mm thick) causes arch fracture during drilling - Entry too SUPERIOR above posterior arch into soft tissue and venous plexus - no bony purchase - Entry too INFERIOR below arch-lateral mass junction onto C1-C2 facet capsule - misses lateral mass ### Step 6: C1 Lateral Mass Screw - Trajectory & Drilling C1 Lateral Mass Screw - Trajectory & Drilling: C1 screw TRAJECTORY: 10-15° MEDIAL toward midline (target is anterior tubercle of C1 on midline), 0-10° CEPHALAD (slight upward angle). Visualize trajectory on LATERAL FLUOROSCOPY: Aim toward C1 ANTERIOR TUBERCLE which appears as anterior bump on C1 ring on lateral view. Screw should parallel superior surface of C1 lateral mass. Use 2.5mm or 3.0mm drill bit with DEPTH STOP set at 28mm (prevents excessive anterior penetration toward internal carotid). Hand-held drill (preferred for tactile feedback) or power drill on slow speed. Drill trajectory 10-15° medial under lateral fluoroscopy guidance. On lateral fluoro, drill bit should advance parallel to C1 superior surface toward anterior tubercle. DEPTH: 20-28mm to reach anterior cortex (measure on preoperative CT for each patient - C1 size varies). FEEL for anterior cortex resistance (hard stop). After drilling to depth, PROBE 4 walls with ball-tip probe: LATERAL wall (MOST critical - breach here is VA 2-3mm lateral), medial wall (breach into C1 canal less critical - wide canal 16-20mm), superior wall, inferior wall. CRITICAL CHECK: Any soft tissue felt laterally indicates VA breach - ABORT screw on that side and consider alternative fixation (contralateral C1 screw plus C2 bilateral, or occiput-C2 fusion). **Technical Tip**: EXAM KEY: C1 lateral mass screw trajectory is 10-15° MEDIAL toward anterior tubercle, slight cephalad 0-10°. I drill under LATERAL FLUOROSCOPY watching real-time. On lateral view, my drill bit should parallel C1 superior surface and aim anteriorly toward anterior tubercle (visible as bump on anterior C1 ring). Depth 20-28mm - I measure on each patient's preoperative CT (C1 size varies - women and Asians smaller). I drill until I FEEL anterior cortex resistance. After drilling, I probe 4 walls with ball-tip probe. LATERAL wall is CRITICAL - if I feel soft tissue or no bone laterally, I have breached into VA groove and MUST abort screw. Medial breach less critical (C1 canal is wide 16-20mm). I prefer BICORTICAL purchase engaging anterior cortex for maximum pullout strength (300-400N bicortical vs 200N unicortical). - Lateral breach into VA groove causes VERTEBRAL ARTERY injury (2-4% incidence) - posterior circulation stroke risk, death if bilateral - Excessive cephalad angle (greater than 15°) causes breach superior into occiput or soft tissue - Insufficient medial angle (less than 10°) directs screw laterally toward VA - Drill too deep (greater than 30mm) risks internal carotid artery anterior (15-20mm from anterior tubercle) - rare but catastrophic - Drill without depth stop risks runaway into pharynx or carotid ### Step 7: C1 Lateral Mass Screw Insertion C1 Lateral Mass Screw Insertion: Select screw size: Diameter 3.5mm (standard) or 4.0mm (if large lateral mass greater than 18mm wide). Length 24-30mm based on probing depth and preoperative CT measurement (typically 26-28mm). Thread screw TYPE: Fully threaded preferred for bicortical purchase. Insert C1 lateral mass screw by HAND initially to feel cortical engagement - should feel resistance at posterior cortex (entry), then smooth passage through cancellous bone of lateral mass, then second resistance at anterior cortex (bicortical purchase). Hand-tighten until screw head is FLUSH or slightly recessed (1mm) into posterior arch surface. Avoid screw head proud (elevated) which makes rod placement difficult. Use screwdriver with tactile feedback. Confirm on BIPLANAR FLUOROSCOPY: (1) LATERAL view: Screw parallels C1 superior surface, tip at or just beyond anterior cortex of lateral mass, screw aimed toward anterior tubercle. (2) AP view: Screw converges medially from entry point, tip medial to entry. Repeat for CONTRALATERAL C1 screw. Final fluoroscopy both C1 screws: AP shows bilateral symmetric screws converging medially (due to 10-15° medial trajectory), lateral shows both screws parallel to C1 ring. Save images to PACS. **Technical Tip**: EXAM KEY: C1 lateral mass screws are 3.5mm diameter, 24-30mm length (most commonly 26-28mm). I insert BICORTICAL for best pullout strength (300-400N vs 200N unicortical). I hand-tighten to feel two cortices - posterior at entry and anterior at tip. Screw head should be flush or slightly recessed. On final fluoroscopy, LATERAL view is most important: Screws should parallel C1 superior surface, NOT be in VA groove (superior aspect of C1 arch). AP view shows symmetric bilateral screws converging medially as expected. Common error: Screws too lateral on AP view or too superior on lateral view indicates VA risk. Optimal trajectory: Medial convergence visible on AP, parallel to C1 superior surface on lateral. - Screw too lateral (visible on AP or lateral fluoro) indicates VA groove penetration or impingement - Screw too long (greater than 30mm) risks internal carotid anterior (rare case reports of ICA injury) - Screw too short (less than 24mm unicortical) risks inadequate pullout strength and screw loosening - Overtightening screw fractures thin C1 posterior arch (3-5mm thick bone) - loss of fixation - Screw head proud (elevated) prevents rod seating and requires screw removal and re-insertion ### Step 8: C2 Pedicle Screw - Entry Point C2 Pedicle Screw - Entry Point: C2 pedicle (also called pars or isthmus - same structure anatomically) ENTRY POINT: MEDIAL and HIGH on C2 superior articular facet. THREE LANDMARKS: (1) 3-5mm from midline (medial to C2 lateral mass), (2) 3mm superior to inferior border of C2 lamina, (3) Medial-superior QUADRANT of junction between C2 superior articular process and lamina. Palpate C2 superior articular facet (ridge of bone). Entry is where lamina meets superior facet medially and superiorly. C2 nerve ganglion must be retracted or sacrificed (usually sacrificed as per Step 4) to clearly visualize entry. Use high-speed burr to remove soft tissue and create starter hole 2-3mm deep at entry point. Confirm entry with ball-tip probe - should palpate solid bone medially (lamina), laterally (pedicle), inferiorly (lamina), superiorly (pars). On LATERAL FLUOROSCOPY, entry point should be at junction of C2 lamina and superior articular process (SAP) when viewing C2 from side. Entry too lateral misses pedicle and goes into C2 lateral mass (weak purchase). Entry too medial is direct into spinal canal. Preoperative CT reviewed again: C2 pedicle width (need at least 3mm for safe 3.5mm screw), pedicle medial angle (typically 20-30°), pedicle cephalad angle (15-25°). **Technical Tip**: EXAM KEY: C2 pedicle entry point is MEDIAL and HIGH - I use three landmarks to find it: (1) 3-5mm from midline (very medial on C2), (2) 3mm superior to inferior lamina edge, (3) Medial-superior quadrant of C2 superior facet-lamina junction. This is where pedicle begins. C2 ganglion MUST be removed (usually sacrificed) to see entry clearly - attempting entry with nerve in place is blind and dangerous. I use burr to clearly define entry creating small starter hole. On lateral fluoro, entry should be at lamina-SAP junction. Preoperative CT confirms pedicle width - if less than 3mm, I abandon pedicle screw and use translaminar screws instead. Pedicle trajectory is steep: 20-30° medial and 15-25° cephalad - this is HIGH-RISK drilling. - Entry too LATERAL misses pedicle, goes into C2 lateral mass or facet (weak unicortical purchase) - Entry too MEDIAL is direct entry into spinal canal - quadriplegia risk - Entry too INFERIOR into C2-C3 facet joint causes facet violation and pain - Inadequate C2 nerve removal obscures entry point leading to blind drilling ### Step 9: C2 Pedicle Screw - Trajectory & Drilling C2 Pedicle Screw - Trajectory & Drilling: C2 pedicle TRAJECTORY: 20-30° MEDIAL toward tip of odontoid (dens), 15-25° CEPHALAD parallel to C2 superior endplate. This trajectory keeps screw in narrow pedicle corridor (4-8mm wide) between spinal canal medially and VA transverse foramen laterally. Use 2.5mm or 3.0mm drill bit with depth stop at 28mm. Drill under BIPLANAR FLUOROSCOPY (AP and lateral SIMULTANEOUSLY) - this is critical for C2 pedicle. On LATERAL fluoro: Screw should parallel C2 SUPERIOR ENDPLATE (15-25° cephalad), heading anteriorly into C2 body. On AP fluoro: Screw should converge MEDIALLY toward MIDLINE ODONTOID TIP. Watch both views continuously during drilling. TECHNIQUE: Start drill at entry, aim medially 20-30° and cephalad 15-25°, advance slowly (1-2mm increments) checking biplanar fluoro after each advance. Drill should stay centered in pedicle on AP view (between medial and lateral cortex). Depth 20-28mm reaches C2 body for bicortical purchase. FEEL for resistance: Hard cortical bone at entry, softer cancellous in pedicle and body, then hard anterior cortex if bicortical. After drilling, PROBE 4 walls: MEDIAL wall (most important - breach is spinal canal), LATERAL wall (breach is VA), superior and inferior walls. Gentle probing - if any soft tissue or no bone, indicates breach. **Technical Tip**: EXAM KEY: C2 pedicle drilling is HIGHEST-RISK step - VA lateral, canal medial, narrow corridor 4-8mm. I use BIPLANAR fluoroscopy watching AP and lateral SIMULTANEOUSLY. Trajectory 20-30° MEDIAL toward odontoid tip on AP, 15-25° CEPHALAD parallel to C2 superior endplate on lateral. I drill slowly, 1-2mm at a time, checking fluoro continuously. On AP, screw must converge toward midline odontoid - if screw trajectory is lateral or parallel, I am missing pedicle going lateral toward VA. On lateral, screw must parallel superior endplate - if screw trajectory is horizontal or inferior, I am missing pedicle. After drilling, I probe MEDIAL wall (breach = canal = quadriplegia) and LATERAL wall (breach = VA = stroke). Depth 20-28mm bicortical into C2 body gives best purchase. - Medial breach into spinal canal causes spinal cord injury and quadriplegia (less than 1% but catastrophic) - Lateral breach into VA transverse foramen causes vertebral artery injury (2-4%), posterior circulation stroke - Inferior trajectory misses pedicle, breaches inferior cortex into C2-C3 or C2 nerve - Insufficient medial angle (less than 20°) directs screw laterally toward VA foramen - Drilling without continuous biplanar fluoroscopy is blind and dangerous - trajectory errors not recognized until breach ### Step 10: C2 Pedicle Screw Insertion (or Translaminar Alternative) C2 Pedicle Screw Insertion (or Translaminar Alternative): C2 PEDICLE SCREW insertion: Select screw 3.5mm diameter (standard) or 4.0mm (if pedicle greater than 6mm wide), length 22-28mm based on drilling depth. Fully threaded screw preferred. Insert by hand initially to feel cortical engagement. Should feel resistance at posterior cortex (entry), smooth passage through pedicle and into C2 body, then resistance at anterior cortex if bicortical. Hand-tighten until screw head flush. Confirm on BIPLANAR fluoroscopy: (1) AP view: Screw converges medially toward odontoid, tip medial to entry, screw entirely within pedicle-body shadow (not breached laterally into facet or medially into canal). (2) LATERAL view: Screw parallels C2 superior endplate, tip in anterior C2 body or at anterior cortex. Repeat for contralateral C2 pedicle screw. ALTERNATIVE if C2 pedicle less than 3mm or VA anomaly: C2 TRANSLAMINAR SCREWS (Wright technique). Entry lateral on C2 lamina 5-8mm from midline on one side. Trajectory 15-20° across midline, courses within C2 lamina substance, exits contralateral lamina. Parallel to C2 inferior endplate on lateral fluoro. Screw 3.5mm diameter, 30-35mm length crosses lamina. Advantage: Completely avoids VA (lateral to lamina) and pedicle. Biomechanics equivalent to pedicle screws for C1-C2 fusion stability. Requires intact C2 lamina. **Technical Tip**: EXAM KEY: C2 pedicle screws are 3.5mm diameter, 22-28mm length. I insert bicortical into C2 body for best purchase (600-800N pullout). On final fluoroscopy, AP view most important: Screws should converge medially toward odontoid - this confirms medial trajectory kept screw in pedicle away from lateral VA. Lateral view confirms screws parallel superior endplate. If pedicle less than 3mm on preoperative CT or high-riding VA anomaly, I use C2 TRANSLAMINAR screws instead: Entry lateral on lamina one side, screw crosses midline within lamina, exits contralateral lamina. Length 30-35mm. Translaminar completely avoids VA (safer) with equivalent biomechanics. Studies (Wright 2004): Translaminar 0% VA injury vs pedicle 4%, fusion rate equivalent 96-97%. - C2 pedicle screw medial breach (visible on AP fluoro screw crosses midline excessively) indicates canal penetration risk - C2 pedicle screw lateral breach (visible on AP fluoro screw lateral to pedicle shadow) indicates VA risk - Screw too long (greater than 30mm) risks anterior structures (vertebral artery anteriorly, esophagus, carotid) - Translaminar screw breach superior (visible on lateral fluoro) into spinal canal causes cord injury - Translaminar screw requires intact lamina - cannot use if previous laminectomy or lamina fracture ### Step 11: Reduction Verification & Rod Contouring Reduction Verification & Rod Contouring: VERIFY C1-C2 REDUCTION on lateral fluoroscopy before rod placement. Measure ADI (should be less than 3mm reduced). If subluxation persists (ADI greater than 3mm): Use screw heads as JOYSTICKS to manipulate C1-C2 into reduction. Can compress C1-C2 (push C1 posterior or C2 anterior), distract slightly, translate. Screw-rod technique advantage over transarticular or wiring: Reduction AFTER screw placement using screws as handles. Provisional reduction achieved, proceed to rods. MEASURE rod length: Distance from C1 screw tulip to C2 screw tulip (typically 25-35mm depending on patient size and C1-C2 height). Select 3.5mm diameter cervical rod (standard) or 4.0mm rod (if 4.0mm screws used). CONTOUR rod to match C1-C2 anatomy: Slight LORDOSIS (C1 anterior to C2 on lateral view - natural cervical lordosis). Gentle curve without sharp bends (stress riser). Use rod bender to create smooth curve. Rod should lie naturally against both screw tulip heads without excessive force. Pre-contour BEFORE insertion - difficult to bend rod once inserted. **Technical Tip**: EXAM KEY: Before rod insertion, I verify reduction on lateral fluoro - ADI should be less than 3mm. If not reduced, I use screw tulips as HANDLES to manipulate C1-C2: I can compress (push C1 posterior using C1 screw heads, or push C2 anterior using C2 screws), distract, translate. This is major advantage of Harms technique over Magerl transarticular (which requires perfect reduction before screw insertion). Once reduced, I measure rod length from C1 to C2 screw tulips - typically 25-35mm (shorter than subaxial rods). I contour rod to slight lordosis matching natural C1-C2 alignment. Rods too straight cause kyphosis. I use smooth bends, no sharp angles. Some systems have offset connectors if screw heads not perfectly aligned. - Proceeding with unreduced C1-C2 (ADI greater than 3mm) results in persistent instability, pain, possible non-union - Over-distraction widens C1-C2 gap reducing facet contact and fusion surface (non-union risk) - Rod contour too kyphotic or lordotic causes cervical malalignment and adjacent segment stress - Rod too short does not span C1-C2 adequately; rod too long extends beyond screws complicating insertion ### Step 12: Rod Placement & Compression Rod Placement & Compression: Insert pre-contoured rod into C1 screw tulip (superior) first using rod holder. Maneuver rod down into C2 screw tulip (inferior) using rod holder and persuader (pusher). May require slight manipulation of screw tulip positions using reduction tabs or towers. Provisionally tighten set screws at both C1 and C2 screws (finger-tight, not final torque) to hold rod in place. Repeat for contralateral rod. Once bilateral rods provisionally placed, apply COMPRESSION across C1-C2 using compression instrument on rod. Compression closes C1-C2 FACET JOINT (lateral atlantoaxial joint) improving fusion surface contact. Compress 3-5mm watching lateral fluoroscopy - ADI should decrease, C1-C2 facets should approximate. Compression also reduces any residual subluxation. CRITICAL for fusion: Compression brings posterior elements together and closes facet joints where fusion occurs. After compression applied and held, FINAL tighten all set screws (C1 bilateral, C2 bilateral = 4 set screws total) to manufacturer specified torque (typically 4-6 Nm for cervical systems using torque-limiting screwdriver). Check construct stability manually by gently stressing - should feel RIGID with no motion. Final fluoroscopy AP and lateral: C1-C2 reduced, screws in good position, rods connect smoothly. **Technical Tip**: EXAM KEY: Rod insertion sequence: C1 tulip first (superior), then seat into C2 tulip (inferior). I provisionally tighten set screws, then apply COMPRESSION across C1-C2 - this is CRITICAL step for fusion. Compression closes C1-C2 facet joints where fusion occurs. I compress 3-5mm watching lateral fluoro. ADI decreases, posterior elements approximate. After compression, I final tighten all 4 set screws to torque (typically 4-6 Nm cervical). Construct should feel RIGID - any motion indicates inadequate fixation (loose set screw, broken rod, pulled-out screw). Final fluoro confirms reduction and hardware position. Some systems have reduction tabs or towers that help rod insertion and compression. - Inadequate compression leaves C1-C2 gap reducing fusion surface contact (pseudarthrosis risk) - Over-compression (greater than 5mm) can fracture osteoporotic C2 pedicle or body - Set screws inadequately tightened (less than manufacturer torque) leads to rod slippage and loss of reduction - Rod slippage from tulip during compression (if set screws not provisionally tightened) causes construct failure ### Step 13: Decortication & Bone Grafting C1-C2 Decortication & Bone Grafting C1-C2: FUSION is essential goal - hardware provides stability but BONE fusion is needed for long-term success. Hardware alone without fusion will eventually fail (fatigue fracture). DECORTICATION C1-C2 posterior elements: (1) C1-C2 FACET JOINTS (lateral atlantoaxial joints): This is PRIMARY fusion site. Use small curette and burr to completely remove articular cartilage from both C1 inferior facet and C2 superior facet. Expose bleeding cancellous bone. May need to cut facet capsule and distract joint slightly to visualize cartilage. Remove all cartilage completely. (2) C1 POSTERIOR ARCH: Use burr to roughen (decorticate) posterior surface of C1 arch creating bleeding bone. Do not thin arch excessively (already thin 3-5mm). (3) C2 LAMINA: Burr to decorticate posterior surface of C2 lamina. Can remove C2 spinous process for autograft (if not needed for instrumentation). All surfaces should be bleeding cancellous bone after decortication. BONE GRAFT: Pack morselized graft into C1-C2 facet joints bilaterally (most important site). Pack over C1 posterior arch and C2 lamina. Graft options: (1) Local AUTOGRAFT from C2 spinous process (morselized), (2) ALLOGRAFT morselized cancellous chips, (3) Iliac crest autograft (stronger but donor site morbidity). Pack generously - use 10-15cc total graft. Some surgeons place structural graft (corticocancellous) wired between C1 arch and C2 spinous process (Gallie technique supplement). BMP (recombinant bone morphogenetic protein) OFF-LABEL at C1-C2 - some use, but risk of soft tissue swelling causing dysphagia or airway compromise at craniovertebral junction - most avoid BMP here. **Technical Tip**: EXAM KEY: C1-C2 fusion occurs primarily at FACET JOINTS (lateral atlantoaxial joints). I decorticate facets COMPLETELY removing all cartilage with curette exposing bleeding bone - this is most important step for fusion. I pack facets generously with bone graft (morselized allograft or local autograft from C2 spinous process). I also decorticate C1 arch and C2 lamina and pack graft over posterior elements. Local autograft from C2 spinous process is excellent if available (removed during exposure). Allograft works well - fusion rate 88-90% allograft vs 95% autograft (small difference, worth avoiding iliac donor site). I AVOID BMP at C1-C2 due to soft tissue swelling risk causing dysphagia or airway obstruction. Evidence: Screw-rod construct fusion rate 95-98% without BMP. Adequate decortication and graft more important than graft type. - Inadequate decortication (cartilage remaining) is leading cause of pseudarthrosis (fusion failure rate 10-15% without good decortication) - BMP use at C1-C2 causes soft tissue swelling with dysphagia risk and possible airway obstruction (avoid) - Excessive bone graft migration into spinal canal (rare) causes cord compression - Over-aggressive decortication of C1 arch thins bone excessively causing arch fracture and screw pullout ### Step 14: Final Imaging & Hemostasis Final Imaging & Hemostasis: Obtain final biplanar fluoroscopy images before closure. VERIFICATION on AP fluoroscopy: (1) Bilateral C1 lateral mass screws symmetric, converging medially as expected from 10-15° medial trajectory. (2) Bilateral C2 pedicle or translaminar screws converging toward midline odontoid (if pedicle) or crossing midline within lamina (if translaminar). (3) No obvious cortical breaches (though fluoro only 60-70% sensitive - postop CT more sensitive). VERIFICATION on LATERAL fluoroscopy: (1) ADI less than 3mm (reduced and maintained). (2) C1 screws parallel to C1 superior surface, not in VA groove superiorly. (3) C2 screws parallel to C2 superior endplate if pedicle screws. (4) Rods connect C1-C2 smoothly with slight lordosis. (5) Bone graft visible over posterior elements. Save all images to PACS with labels (AP C1-C2, lateral C1-C2). HEMOSTASIS: Critical step - cervical hematoma causes airway obstruction. Copious irrigation with normal saline or antibiotic solution. Bipolar cautery for all bleeding points. Venous plexus oozing controlled with thrombin-soaked Gelfoam packing over C1-C2. Bone wax for bony ooze if needed (though avoid excessive wax which inhibits fusion). Achieve meticulous hemostasis - take time. Place Valsalva maneuver (increase ventilator pressure to 30-40cm H2O for 10-15 seconds) to identify venous bleeding. Release Mayfield and check pin sites for scalp bleeding - control with Raney clips or sutures. **Technical Tip**: EXAM KEY: Final imaging is MANDATORY before closure. I verify screw positions and reduction on biplanar fluoro and save images to PACS. On lateral view, I confirm ADI less than 3mm (reduced and maintained throughout procedure). C1 screws should parallel C1 superior surface (not in VA groove). C2 screws parallel superior endplate. On AP view, screws converge medially as expected. I document images because postoperative complications (VA injury, neurological deficit) require review of intraoperative screw positions. Hemostasis critical at C1-C2: Cervical hematoma causes airway obstruction emergency. I use copious bipolar, Gelfoam with thrombin, patience. Valsalva maneuver identifies venous bleeders. I check Mayfield pin sites - can bleed significantly. - Unrecognized screw malposition (medial breach into canal, lateral breach into VA) may cause delayed neurological deficit or VA thrombosis - Inadequate hemostasis leads to postoperative hematoma (1-2% at C1-C2) causing airway obstruction (emergency) - Proceeding without final imaging documentation creates medicolegal risk if complications occur - Missed Mayfield pin site bleeding causes scalp hematoma and wound complications ### Step 15: Closure & Postoperative Care Closure & Postoperative Care: Place subfascial drain (10-12Fr Blake or Jackson-Pratt) in deep layer over hardware. Secure drain to skin and connect to bulb suction. Drain prevents hematoma accumulation. Exit drain laterally through separate stab incision (not through main wound). Close in layers: (1) LIGAMENTUM NUCHAE and midline raphe with 0 or 1 absorbable suture (Vicryl or PDS) - this is key structural layer reapproximating paraspinal muscles. (2) Deep subcutaneous layer with 2-0 absorbable interrupted or running. (3) Superficial subcutaneous layer with 3-0 absorbable. (4) Skin: Staples (faster, easier removal) or subcuticular 3-0 or 4-0 absorbable suture (better cosmesis). Apply sterile dressing (Tegaderm or gauze with tape). Hard cervical collar (Philadelphia or Miami-J) applied BEFORE moving patient from prone to supine (maintain neck stability during transfer). POSTOPERATIVE immediate: Transfer to ICU or monitored bed. Watch for AIRWAY SWELLING first 24 hours - C1-C2 has higher risk than subaxial due to proximity to pharynx. Monitor for stridor, dyspnea, dysphagia. Lower threshold to intubate or reopen wound if hematoma. Neuromonitoring: Immediate wake-up neurological exam in OR - all four extremities motor and sensory, cranial nerves. Repeat neuro checks every 2 hours first 24 hours. Drain management: Remove when output less than 30mL per 24 hours (typically day 1-2). Do not leave drain more than 48 hours. Collar: Continuous wear 24/7 for 8-12 weeks. Mobilize day 1-2 with physical therapy. DVT prophylaxis (enoxaparin or sequential compression devices). Discharge day 2-4 when pain controlled, ambulating, drain removed. **Technical Tip**: EXAM KEY: I ALWAYS place drain after C1-C2 fusion - hematoma risk higher than subaxial and causes AIRWAY OBSTRUCTION (emergency). First 24 hours I monitor closely for airway compromise - stridor, dyspnea, neck swelling. C1-C2 hematoma compresses pharynx causing dysphagia and airway compromise faster than subaxial hematoma. Lower threshold to reopen wound or intubate. Immediate wake-up exam checks all four extremities and cranial nerves - unrecognized VA injury can cause delayed posterior circulation stroke (cerebellar, brainstem). Collar worn continuously 8-12 weeks - longer than subaxial (6 weeks typical) because C1-C2 biomechanical stress is higher (50% rotation occurs here). Fusion confirmed on CT at 6-12 months showing bridging bone across C1-C2 facets bilaterally. - Postoperative hematoma (1-2% incidence at C1-C2) causes airway obstruction requiring emergency reintubation or reopening - Unrecognized neurological deficit from screw malposition or VA injury - check immediately postoperatively - Occipital neuralgia from C2 nerve sacrifice (20-30% dysesthesias, less than 5% chronic pain) - counsel patient this is expected - Vertebral artery injury delayed presentation: Posterior circulation stroke symptoms (ataxia, vertigo, diplopia, dysphagia) within 24-72 hours - Inadequate collar compliance or early removal leads to pseudarthrosis (fusion failure) **Immediate (0-24 hours)**: ICU or monitored bed for airway monitoring (C1-C2 hematoma higher risk than subaxial). Subfascial drain to bulb suction, remove when less than 30mL per 24 hours (day 1-2). Neurological examination immediate wake-up (all four extremities, cranial nerves) and every 2 hours first 24 hours. Watch for stridor, dyspnea (airway obstruction), posterior circulation stroke symptoms (ataxia, vertigo, diplopia from VA injury). Hard cervical collar (Philadelphia or Miami-J) continuously. Pain control multimodal (acetaminophen, opioids PRN, muscle relaxants). **Early Mobilization (Days 1-7)**: Mobilize day 1 out of bed to chair, ambulation day 1-2 with physical therapy and collar on. Soft diet initially (dysphagia risk 10-20% transient). DVT prophylaxis (enoxaparin 40mg subcutaneous daily or hospital protocol, sequential compression devices). Wound care (transparent dressing, remove day 2-3, keep clean and dry). Discharge day 2-4 when pain controlled, ambulating, drain removed. **Outpatient Follow-Up**: Week 2 (wound check, remove staples/sutures, assess collar compliance, neurological exam), Week 6 (upright lateral X-ray in collar, assess pain and stability), Week 8-12 (flexion-extension X-rays to assess fusion progress, wean collar if stable), Month 3-4 (flexion-extension X-rays off collar for motion less than 2mm translation or less than 5° rotation), Month 6-12 (CT confirms fusion with bridging bone across C1-C2 facets bilaterally). **Return to Activities**: Desk work 6-8 weeks (typing possible in collar), driving after collar discontinued 8-12 weeks AND fusion stable (counsel about permanent 50% rotation loss affecting blind spot checking), physical labor after fusion confirmed on CT 6-12 months, contact sports controversial (most recommend permanent discontinuation). **Collar Protocol**: Hard collar continuously 24/7 for 8-12 weeks (longer than subaxial 6 weeks due to high biomechanical stress at C1-C2). Remove only for wound care first 2 weeks, then for showering if stable. Wean gradually over 1-2 weeks at 8-12 weeks if flexion-extension films stable. ## References 1. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976). 2001;26(22):2467-2471. *Original description of Harms technique with 100% fusion rate in 37 patients, zero VA injuries* 2. Goel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien). 1994;129(1-2):47-53. *Independent description of identical technique to Harms, 160 patients with 98% fusion rate* 3. Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004;17(2):158-162. *Translaminar screw technique avoiding VA completely, 0% VA injury versus 4% with pedicle screws* 4. Ma XY, Yin QS, Wu ZH, et al. C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities. Spine (Phila Pa 1976). 2009;34(4):371-377. *Biomechanical study: C1 lateral mass bicortical 300-400N versus unicortical 200N pullout strength* 5. Yeom JS, Buchowski JM, Park KW, et al. Undetected vertebral artery groove and foramen violations during C1 lateral mass and C2 pedicle screw placement. Spine (Phila Pa 1976). 2008;33(25):E942-E949. *Postoperative CT analysis: 5-15% cortical breaches, less than 3% symptomatic; fluoroscopy only 60-70% sensitive* 6. Elliott RE, Tanweer O. The prevalence of high-riding vertebral arteries and other anatomical variants that pose a surgical challenge in C1-C2 fixation: a radiographic study in a multicenter cohort of 1,101 patients. J Neurosurg Spine. 2014;21(6):897-906. *VA anomalies in 18-20%: high-riding VA, fenestration, persistent first intersegmental artery contraindicate pedicle screws* 7. Hott JS, Deshmukh VR, Klopfenstein JD, et al. Intraoperative Iso-C C-arm navigation in craniospinal surgery: the first 60 cases. Neurosurgery. 2004;54(5):1131-1136. *C2 nerve sacrifice outcomes: 20-30% temporary dysesthesias, less than 5% chronic significant pain, 92% patient satisfaction* 8. Madawi AA, Casey AT, Solanki GA, et al. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg. 1997;86(6):961-968. *Transarticular screws: 4-8% VA injury rate versus 2-4% with Harms technique; 20% cannot have bilateral screws due to VA anatomy* 9. Gorek J, Acaroglu E, Berven S, et al. Constructs incorporating intralaminar C2 screws provide rigid stability for atlantoaxial fixation. Spine (Phila Pa 1976). 2005;30(13):1513-1518. *Biomechanics: Translaminar screws 550-700N pullout equivalent to pedicle 600-800N, superior to wiring 150-250N* 10. Ma XY, Yin QS, Wu ZH, et al. Anatomic considerations for the pedicle screw placement in the first cervical vertebra. Spine (Phila Pa 1976). 2005;30(13):1519-1523. *C1 lateral mass anatomy: 15-20mm thick at arch-lateral mass junction, VA 2-3mm lateral, safe corridor 10-15° medial trajectory*

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

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