import { OnePagerSummary, ExamWarning, InfoCardGrid, InfoCard, MnemonicCard, EvidenceCard, VivaScenarioSection, VivaScenario, ExamCheatSheet, ContentSection, ExamPearl, SafetyAlert, NumberHighlightRow, NumberHighlight, Tabs, Tab, ComparisonTable } from '@/components/mdx' **Recurrent laryngeal nerve** - LEFT: predictable course, loops under aortic arch, ascends in tracheoesophageal groove. RIGHT: loops under subclavian, more variable, may be lateral. Injury causes hoarseness. **Superior laryngeal nerve (external branch)** - Runs with superior thyroid artery at C3-C4 level. Injury causes voice fatigue, pitch problems (cricothyroid muscle). **Sympathetic chain** - On anterolateral vertebral bodies, under lateral longus colli. Injury causes Horner syndrome (miosis, ptosis, anhidrosis). **Carotid sheath (carotid artery, IJV, vagus nerve)** - Lateral to operative field. Vagus gives off RLN. Retract gently laterally. **Vertebral artery** - In transverse foramen of C1-C6, 14-18mm from midline. Risk during lateral decompression/foraminotomy. **Esophagus** - Posterior to trachea, medial retraction. Perforation rate 0.1-0.5%, potentially fatal. Higher risk with revision, long retraction. **Spinal cord and nerve roots** - Dura immediately posterior to PLL (no epidural space anteriorly). Decompression must be controlled. **Thoracic duct** - Left-sided, enters jugular-subclavian junction. Risk at C6-C7/T1 on left. Injury causes chyle leak. **Primary Indications:** - Cervical radiculopathy from disc herniation with dermatomal symptoms correlating to imaging - Cervical radiculopathy from osteophyte/foraminal stenosis causing nerve root compression - Cervical myelopathy with cord compression (single level - ACDF preferred over posterior) - Failed 6-12 weeks conservative management for radiculopathy **Relative Indications:** - Axial neck pain from degenerative disc disease (less predictable outcomes) - Soft disc herniation with motor deficit (relative urgent indication) - Cervical instability requiring fusion (trauma, tumor, infection - single level) **ACDF vs Posterior Approach:** - ACDF preferred for 1-2 levels, anterior pathology (soft disc, osteophyte) - Posterior preferred for 3+ levels, posterior pathology, kyphosis correction - Combined anterior-posterior for severe instability, multilevel with kyphosis **Expected Outcomes:** - Radiculopathy: 90-95% good/excellent outcomes - Myelopathy: 80% improvement or stabilization (less predictable than radiculopathy) - Fusion rate: 95%+ with plate at single level **Absolute Contraindications:** - Active cervical spine infection (relative - may still need surgery with debridement) - Severe medical comorbidities precluding general anesthesia - No identifiable structural pathology correlating to symptoms **Relative Contraindications:** - Severe osteoporosis (poor screw purchase, subsidence risk) - Previous anterior cervical surgery (increased RLN injury risk on same side) - Previous neck irradiation (wound healing risk, esophageal fragility) - Severe kyphotic deformity (posterior approach may be better) - Multi-level disease (3+ levels - consider posterior or staged) - Diffuse idiopathic skeletal hyperostosis (DISH) - ossification risk **Patient Counselling Points:** - Dysphagia common initially (50%), usually resolves - Hoarseness risk (2-11% temporary, <1% permanent) - Adjacent segment disease long-term (2-3%/year) - Smoking significantly impairs fusion (counsel cessation) **Essential Imaging:** - Cervical spine X-rays (AP, lateral, flexion-extension): assess alignment, instability, osteophytes - MRI cervical spine: disc herniation, cord signal change, nerve root compression, cord compression - CT cervical spine (if needed): bony anatomy, osteophyte configuration, foramen dimensions **Clinical Correlation:** - Radiculopathy: dermatomal pain/numbness, myotomal weakness, reflex changes - Myelopathy: gait disturbance, hand clumsiness, hyperreflexia, positive Hoffmann/Babinski - Must correlate imaging level to clinical findings (don't operate on asymptomatic degeneration) **Special Investigations:** - EMG/nerve conduction studies: if diagnosis unclear, differentiate from peripheral neuropathy - CT myelogram: if MRI contraindicated or unclear findings - Dynamic X-rays: assess stability if concern for listhesis **Pre-operative Optimization:** - Smoking cessation (minimum 4-6 weeks pre-op, continue post-op) - Optimize diabetes control (HbA1c target <8%) - Review anticoagulation (bridge vs hold based on thrombotic risk) - Laryngoscopy pre-op if previous anterior neck surgery (assess RLN function) **Positioning:** - Radiolucent table or Jackson frame - Shoulder roll (small - extends neck) - Head ring or Mayfield attachment (optional) - Shoulder tape for caudal traction (lower levels) **Surgical Instruments:** - Self-retaining retractor system (Caspar, Cloward, or equivalent) - Caspar distraction pins and distractor - High-speed burr with various sizes (3-5mm) - Kerrison rongeurs (1-3mm) - Curettes (various sizes) - Pituitary rongeurs - Nerve hooks and dissectors **Implants:** - Interbody cage: PEEK (radiolucent), titanium, or allograft bone - Cage sizing trials - Anterior cervical plate and screws (variable angle preferred) - Bone graft: local autograft, allograft chips, synthetic bone substitute **Imaging:** - C-arm fluoroscopy (essential for level confirmation) - Neuromonitoring: MEPs, SSEPs, EMG (strongly recommended) - Consider intraoperative CT if available (complex cases) **Surface Anatomy:** - C2-C3: angle of mandible - C3-C4: hyoid bone - C4-C5: thyroid cartilage (thyrohyoid notch) - C6: cricoid cartilage (most reliable landmark) - C7: carotid tubercle (Chassaignac's tubercle) on transverse process **Smith-Robinson Interval:** - Avascular plane between SCM/carotid sheath laterally and strap muscles/trachea/esophagus medially - Strap muscles: sternohyoid, sternothyroid, omohyoid - Omohyoid crosses operative field at C5-C6 level - can retract or divide - Deep cervical fascia envelopes all structures **Vertebral Anatomy:** - Uncovertebral joints (joints of Luschka): lateral to disc, form lateral boundary of foramen - Vertebral artery: enters transverse foramen at C6 (sometimes C7), courses through C6-C1 - Distance from midline to vertebral artery: 14-18mm (be aware during lateral decompression) - Anterior longitudinal ligament (ALL): tough, covers anterior vertebral bodies - Posterior longitudinal ligament (PLL): thinner, covers posterior disc - remove for decompression **Recurrent Laryngeal Nerve:** - LEFT RLN: loops under aortic arch, ascends in tracheoesophageal groove (predictable) - RIGHT RLN: loops under subclavian artery, more variable course, may be more lateral - Most surgeons prefer left-sided approach for more predictable RLN anatomy - Bilateral RLN injury: acute airway obstruction requiring tracheostomy **Sympathetic Chain:** - Runs on anterolateral aspect of vertebral bodies - Located under lateral edge of longus colli muscle - Elevate longus colli subperiosteally and place retractor blades underneath - protects chain - Injury causes Horner syndrome: miosis (small pupil), ptosis, anhidrosis **Patient Position**: Supine with small shoulder roll (extends neck slightly - improves anterior exposure). Head in neutral or slight right rotation if left-sided approach (opens the interval). Arms tucked at sides with padding. All pressure points padded. **Anaesthesia Considerations:** - General anaesthesia with endotracheal intubation - Consider awake fibreoptic intubation if severe myelopathy or instability - Neuromonitoring (MEPs, SSEPs) - establish baseline after induction **Fluoroscopy Setup:** - C-arm positioned for lateral imaging - Tape shoulders caudally for lower cervical levels (C6-T1) - Confirm target level with spinal needle before incision **Skin Marking:** - Transverse incision in skin crease - Center over target level (use surface landmarks as guide) - Typical incision 4-5cm for single level ### Step 1: Positioning and Neuromonitoring Baseline Position supine with shoulder roll (extends neck for exposure). Head neutral or slight right rotation for left-sided approach. Arms tucked, pressure points padded. Tape shoulders caudally for lower cervical levels (C6-T1). Establish neuromonitoring baseline (MEPs, SSEPs) after induction. **Positioning Principles:** - Extension improves anterior exposure but avoid hyperextension in myelopathy (risk of cord compression) - Slight right rotation opens left-sided interval (most surgeons prefer left approach) - Shoulder taping essential for C6-C7/T1 visualization on fluoroscopy - Document neuromonitoring baseline - any deterioration during surgery requires investigation - Hyperextension in myelopathy patient causing cord compression/injury - Pressure injury to occiput, heels, elbows from prolonged positioning - Brachial plexus stretch from arm positioning ### Step 2: Level Localization and Incision Fluoroscopy to identify target disc level using surface landmarks (C4-C5 at thyroid cartilage, C6 at cricoid). Place spinal needle into disc space under fluoroscopy to confirm correct level - MUST obtain lateral image to confirm. Mark transverse skin incision in skin crease at target level. This is the most important step to prevent wrong-level surgery. **Level Confirmation Protocol:** - Surface landmarks as initial guide only (can be unreliable) - Spinal needle placed in disc under fluoroscopy - MUST obtain LATERAL image to confirm level (AP view insufficient) - Wrong-level surgery is a "never event" - document level confirmation - Some surgeons obtain another image after self-retaining retractors placed - Wrong-level surgery - never-event, confirm with fluoroscopy before proceeding - Incision too proximal or distal limiting exposure - Needle injury to esophagus or other structures if not placed correctly ### Step 3: Superficial Dissection to Platysma Transverse skin incision 4-5cm along skin crease. Divide subcutaneous tissue and expose platysma. Divide platysma transversely (fibers run vertically, transverse division reduces tension on closure). Identify deep cervical fascia beneath platysma. **Platysma Division:** - Platysma fibers run obliquely/vertically - Divide transversely to minimize tension on wound closure - Meticulous hemostasis in subcutaneous layer (prevent post-op hematoma) - Protect marginal mandibular branch of facial nerve (superior to operative field) - External jugular vein injury (anterior to SCM) - Marginal mandibular nerve injury (superior - at level of mandible) - Inadequate hemostasis causing post-op hematoma ### Step 4: Development of Smith-Robinson Interval Palpate medial border of SCM. Incise deep cervical fascia along medial border of SCM. Develop avascular plane BETWEEN SCM/carotid sheath laterally (retract laterally) and strap muscles/trachea/esophagus medially (retract medially). This plane is bloodless if developed correctly with blunt finger dissection. **Smith-Robinson Interval Pearls:** - Avascular plane exists if dissection stays in correct tissue plane - Finger dissection sweeps carotid sheath laterally, trachea/esophagus medially - Omohyoid muscle crosses at C5-C6 level - can retract superiorly/inferiorly or divide - Feel carotid pulse laterally to confirm correct interval (should be lateral to retractor) - If bleeding encountered, wrong plane - reassess and redirect - Carotid artery injury if plane too lateral - Esophageal injury if plane too medial or aggressive retraction - IJV injury - retracted with carotid sheath, can tear with aggressive retraction ### Step 5: Exposure of Prevertebral Fascia Continue blunt dissection medially until prevertebral fascia identified (shiny white layer over vertebral bodies). Palpate midline (feel anterior longitudinal ligament and vertebral bodies). Identify disc space (soft) between hard vertebral bodies. Place self-retaining retractor. **Prevertebral Fascia Exposure:** - Shiny white prevertebral fascia covers longus colli muscles and vertebral bodies - Feel for midline - ALL is palpable longitudinal ridge - Disc spaces are soft, vertebral bodies are hard - Elevate longus colli subperiosteally BEFORE placing retractor blades - Retractor blades placed UNDER longus colli to protect sympathetic chain - Sympathetic chain injury if retractor blades placed on top of longus colli (Horner syndrome) - Recurrent laryngeal nerve injury from excessive medial retraction - Wrong level if midline not correctly identified ### Step 6: Level Confirmation and Retractor Placement Insert Caspar distraction pins into vertebral bodies above and below target disc. Confirm level AGAIN with lateral fluoroscopy (second confirmation with retractors in place). Place self-retaining retractor blades UNDER elevated longus colli muscles bilaterally. Apply distraction to open disc space. **Retractor Placement Critical Points:** - Elevate longus colli subperiosteally from midline to 15mm laterally - Place retractor blades UNDER longus colli (protects sympathetic chain) - Release retractors periodically during case (reduces RLN neuropraxia from prolonged retraction) - Caspar pins in vertebral bodies (not endplates) for distraction - Limit distraction to avoid overdistraction and nerve root injury - Sympathetic chain injury if retractor blades superficial to longus colli - Vertebral body fracture from pin placement in osteoporotic bone - RLN injury from prolonged or excessive medial retraction ### Step 7: Discectomy Incise anterior longitudinal ligament (ALL) over disc with scalpel. Remove disc material with pituitary rongeurs and curettes. Use high-speed burr to remove osteophytes from vertebral body margins if present. Proceed posteriorly systematically, removing all disc material to posterior longitudinal ligament (PLL). **Discectomy Technique:** - Complete discectomy to PLL is essential for adequate decompression - Use curettes to scrape disc material from endplates - Burr osteophytes but preserve endplate integrity (prevent subsidence) - Identify posterior annulus and PLL as posterior limit of initial discectomy - Maintain awareness of depth - dura is immediately posterior to PLL - Endplate violation causing subsidence (overly aggressive curetting) - Vertebral artery injury if burr strays too lateral (14-18mm from midline) - Spinal cord injury if instruments pushed posterior through PLL without control ### Step 8: Posterior Decompression (PLL Removal and Foraminotomy) Remove posterior longitudinal ligament (PLL) to visualize dura - there is NO epidural space anteriorly in the cervical spine. Use Kerrison rongeurs to remove PLL and visualize dural pulsations. Perform bilateral foraminotomy by removing medial uncinate processes with Kerrison rongeurs - ensure nerve roots are decompressed. **Decompression Goals:** - PLL removal required for adequate decompression and to visualize dura - No epidural space anteriorly - dura is immediately posterior to PLL - Dural pulsations confirm adequate central decompression - Foraminotomy: remove medial uncinates to decompress exiting nerve roots - Lateral limit of foraminotomy: 14mm from midline (vertebral artery beyond) - Confirm nerve root decompression with nerve hook - should be freely mobile - Dural tear causing CSF leak (rare but requires repair) - Spinal cord contusion from instruments or bone fragments - Vertebral artery injury during foraminotomy (stay within 14mm of midline) - Nerve root injury from Kerrison rongeur during foraminotomy ### Step 9: Endplate Preparation Prepare superior and inferior vertebral endplates by removing cartilage with curettes. Expose bleeding cancellous bone (enhances fusion). Avoid violating endplate integrity (subchondral bone should remain intact - prevents subsidence). Create parallel surfaces for cage seating. **Endplate Preparation Principles:** - Remove cartilaginous endplate to expose bleeding cancellous bone - Preserve subchondral bone plate (prevents cage subsidence) - Create flat, parallel surfaces for optimal cage contact - Bleeding bone essential for fusion (vascular supply for graft incorporation) - Balance between adequate preparation (bleeding bone) and not weakening endplate - Endplate violation causing subsidence (overly aggressive preparation) - Inadequate preparation with residual cartilage (impairs fusion) - Asymmetric preparation causing cage tilt ### Step 10: Cage Insertion Select appropriate interbody cage (PEEK most common, titanium, or allograft). Size cage with trials - should be slight press-fit, restore disc height but avoid overdistraction. Pack cage with bone graft material (local autograft, allograft, synthetic). Insert cage and position flush with anterior vertebral body margin. Confirm position with fluoroscopy. **Cage Selection and Insertion:** - PEEK cages: radiolucent (allows fusion assessment), tantalum markers for position - Titanium cages: better osteointegration but artifact on MRI - Allograft bone: biological option but resorption risk - Height: restore disc height but avoid overdistraction (>2mm increases radiculopathy risk) - Cage should sit flush with or 1-2mm posterior to anterior vertebral body edge - Lordotic cages can help restore cervical lordosis - Cage too large causing overdistraction and radiculopathy - Cage retropulsion (migration posterior) - confirm position on fluoroscopy - Cage subsidence if endplates violated or osteoporotic bone - Inadequate graft packing reducing fusion potential ### Step 11: Anterior Plate Fixation Select plate to span from mid-superior vertebral body to mid-inferior body. Plate provides load-sharing and increases fusion rate (reduces non-union from 10% to 5%). Position plate midline on vertebral bodies. Insert screws with 12-15 degrees convergent trajectory. Confirm plate and screw position with fluoroscopy (AP and lateral). **Plate Fixation Principles:** - Plate provides stability during fusion (load-sharing device) - Screw trajectory: 12-15 degrees toward midline (convergent) for best bone purchase - Avoid lateral cortex breach (vertebral artery, nerve root injury) - Variable-angle screws preferred (allows trajectory adjustment) - Check screw length - avoid posterior cortex breach - Plate reduces non-union rate from ~10% to ~5% for single level - Screw lateral cortex breach (nerve root/vertebral artery injury) - Screw posterior cortex breach (spinal cord injury) - Screw into adjacent disc space (affects adjacent segment) - Plate too long encroaching on adjacent disc (accelerates adjacent segment disease) ### Step 12: Final Checks, Hemostasis, and Closure Remove distractor pins. Confirm neuromonitoring unchanged from baseline. Fluoroscopy to confirm final cage and plate position. Release retractors and allow soft tissues to return to anatomic position. Meticulous hemostasis with bipolar cautery (careful near RLN). Irrigate thoroughly. Drain placement optional (controversial). Close platysma (3-0 Vicryl), subcutaneous (3-0 Vicryl), skin (subcuticular 4-0 Monocryl). **Closure and Post-operative Considerations:** - Release retractors before closure - prolonged retraction increases dysphagia - Check neuromonitoring before closing - investigate any changes - Drain controversial: some evidence reduces hematoma, most surgeons don't use routinely - Extubate awake in OR to assess airway and voice immediately - Monitor for airway compromise post-op (retropharyngeal hematoma) - Soft diet initially (dysphagia common first few days) - Retropharyngeal hematoma causing airway obstruction (catastrophic if missed) - Esophageal injury not recognized (delayed presentation with sepsis) - RLN injury from cautery or traction not recognized until extubation - Inadequate hemostasis causing post-op hematoma and airway compromise 1. Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958;40-A(3):607-624. 2. Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine. 2007;32(21):2310-2317. 3. Bazaz R, Lee MJ, Yoo JU. Incidence of dysphagia after anterior cervical spine surgery: a prospective study. Spine. 2002;27(22):2453-2458. 4. Netterville JL, Koriwchak MJ, Winkle M, et al. Vocal fold paralysis following the anterior approach to the cervical spine. Ann Otol Rhinol Laryngol. 1996;105(2):85-91. 5. Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004;4(6 Suppl):190S-194S. 6. Kaiser MG, Haid RW Jr, Subach BR, et al. Anterior cervical plating enhances arthrodesis after discectomy and fusion with cortical allograft. Neurosurgery. 2002;50(2):229-238. 7. Winslow CP, Winslow TJ, Wax MK. Dysphonia and dysphagia following the anterior approach to the cervical spine. Arch Otolaryngol Head Neck Surg. 2001;127(1):51-55. 8. Apfelbaum RI, Kriskovich MD, Haller JR. On the incidence, cause, and prevention of recurrent laryngeal nerve palsies during anterior cervical spine surgery. Spine. 2000;25(22):2906-2912. 9. Fraser JF, Härtl R. Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine. 2007;6(4):298-303. 10. Epstein NE. Airway complications of multilevel anterior cervical surgery. J Spinal Disord. 2001;14(2):135-140.

Anterior Cervical Discectomy and Fusion (ACDF) - Single Level

Anterior Cervical Discectomy and Fusion (ACDF) - Single Level