High Yield Overview

ANTERIOR CERVICAL DISCECTOMY AND FUSION (ACDF) - SINGLE LEVEL

Smith-Robinson approach | Left-sided transverse incision | Avascular plane medial to carotid sheath | Discectomy with decompression | Cage + anterior plate fixation

Critical Danger Structures

Danger 1

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.

Danger 2

Superior laryngeal nerve (external branch) - Runs with superior thyroid artery at C3-C4 level. Injury causes voice fatigue, pitch problems (cricothyroid muscle).

Danger 3

Sympathetic chain - On anterolateral vertebral bodies, under lateral longus colli. Injury causes Horner syndrome (miosis, ptosis, anhidrosis).

Danger 4

Carotid sheath (carotid artery, IJV, vagus nerve) - Lateral to operative field. Vagus gives off RLN. Retract gently laterally.

Danger 5

Vertebral artery - In transverse foramen of C1-C6, 14-18mm from midline. Risk during lateral decompression/foraminotomy.

Danger 6

Esophagus - Posterior to trachea, medial retraction. Perforation rate 0.1-0.5%, potentially fatal. Higher risk with revision, long retraction.

Danger 7

Spinal cord and nerve roots - Dura immediately posterior to PLL (no epidural space anteriorly). Decompression must be controlled.

Danger 8

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

Mnemonic

MHTCSurface Landmarks for Level Identification

Mnemonic

SCOPESmith-Robinson Approach Key Steps

Surgical Anatomy

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

Positioning and Preparation

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

Operative Technique

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.

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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)

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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).

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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.

Exam Pearl

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

Dangers at this step

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).

Exam Pearl

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

Dangers at this step

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).

Exam Pearl

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)

Dangers at this step

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

Complications

Major Complications - Recognition, Prevention, and Management

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"You are performing a single-level ACDF at C5-C6 on a 45-year-old with radiculopathy. During closure, the anaesthetist mentions the patient is 'a bit stridorous' after extubation. What is your immediate management?"

EXCEPTIONAL ANSWER

This is a potentially life-threatening emergency that requires immediate attention. Stridor post-ACDF suggests airway compromise, most likely from retropharyngeal hematoma, which can progress rapidly to complete airway obstruction. My immediate management would be: First, I would call for senior help and notify the anaesthetic team that this may be an airway emergency. I would ask for an emergency airway trolley and ensure difficult airway equipment is available. I would assess the patient's airway by examining the neck for swelling or bruising, checking voice quality, and assessing respiratory distress. If the patient is maintaining their airway but stridorous, I would keep them calm, upright if possible, and apply supplemental oxygen. If the stridor is progressive or the patient is deteriorating, I would prepare for emergent intubation. However, intubation may be extremely difficult due to hematoma distorting the airway. I would have ENT surgery on standby and prepare for emergency cricothyroidotomy or tracheostomy if intubation fails. In parallel, I would prepare to return to the operating theatre immediately for surgical evacuation. If the patient is deteriorating rapidly and cannot be intubated, I would perform bedside wound evacuation - opening the skin and platysma to release the hematoma and decompress the airway - this can be life-saving even if not in the OR. Once the airway is secured, I would return to theatre for formal wound exploration, evacuation of hematoma, identification and control of the bleeding source, thorough irrigation, and consideration of drain placement before re-closure. The key teaching point is that retropharyngeal hematoma post-ACDF is a surgical emergency. Do not delay intervention hoping it will improve - these can progress from stridor to complete obstruction within minutes. Have a low threshold for re-exploration.

VIVA SCENARIOStandard

EXAMINER

"A patient wakes up from ACDF with a hoarse voice. How do you assess and counsel this patient?"

EXCEPTIONAL ANSWER

Hoarseness immediately post-ACDF suggests recurrent laryngeal nerve dysfunction. This is the most common nerve injury following ACDF, occurring in 2-11% of cases. My assessment and counselling would be systematic. First, I would document the voice change, including severity and whether they can phonate at all. I would ask about cough strength (weak cough suggests aspiration risk) and any swallowing difficulties. I would examine for stridor or respiratory distress, which would suggest more severe bilateral injury or airway compromise. Importantly, the vast majority of RLN injuries post-ACDF are temporary neuropraxia from retraction rather than transection. Approximately 90-95% recover fully within 6-12 weeks as the nerve recovers from the traction insult. For counselling, I would explain that temporary voice changes are common after this surgery, occurring in up to 1 in 10 patients. I would reassure them that this is usually due to nerve stretching from retractors rather than permanent damage, and that recovery is expected over the coming weeks to months. I would advise them to avoid straining their voice and that we will monitor their recovery. I would arrange ENT referral for laryngoscopy to document vocal cord function - this serves as a baseline and determines if the cord is paretic versus paralyzed. If there is concern about aspiration (weak cough, choking with liquids), I would request a speech pathology swallowing assessment. I would schedule follow-up at 6 weeks and 3 months to document recovery. If hoarseness persists beyond 6 months with confirmed vocal cord paralysis on laryngoscopy, I would refer to ENT for consideration of medialization procedures (injection laryngoplasty or thyroplasty). I would also document this complication thoroughly in the medical record, including the discussion with the patient, and notify my consultant.

VIVA SCENARIOStandard

EXAMINER

"Why do many surgeons prefer a left-sided approach for ACDF, and in what situations would you consider a right-sided approach?"

EXCEPTIONAL ANSWER

The preference for a left-sided approach to ACDF relates primarily to the anatomy of the recurrent laryngeal nerve, though other factors also influence the decision. The left recurrent laryngeal nerve has a more predictable course. It loops under the aortic arch in the chest and then ascends in the tracheoesophageal groove to reach the larynx. This consistent path means the nerve is reliably located in the groove between the trachea and esophagus throughout the cervical approach. The right recurrent laryngeal nerve has a more variable course. It loops under the subclavian artery, which is higher in the neck than the aortic arch, resulting in a shorter recurrent course. More importantly, the right RLN may take a more lateral path before entering the tracheoesophageal groove, potentially placing it more at risk during the lateral retraction required for exposure. Some studies have suggested a higher rate of RLN injury with right-sided approaches, though this remains controversial, and other studies show no significant difference. I would consider a right-sided approach in the following situations: First, if the patient has had previous left-sided anterior cervical surgery, I would use the right side to avoid scar tissue and the potentially already-injured left RLN. A second injury to the same nerve could convert hoarseness to complete paralysis, and bilateral RLN injury causes acute airway obstruction requiring tracheostomy. Second, if pre-operative laryngoscopy shows pre-existing left vocal cord paralysis from any cause, I would approach from the right to protect the functioning right cord. Third, if the pathology is predominantly right-sided (right-sided disc herniation or right foraminal stenosis), some surgeons prefer approaching from the side of the pathology for better visualization of the nerve root. Fourth, for surgeons who are experienced and comfortable with right-sided approaches, there may be no meaningful difference in outcomes. Regardless of approach side, the key protective measures remain the same: careful retraction, periodic release of retractors, and meticulous surgical technique.

Anterior Cervical Discectomy and Fusion (ACDF) - Exam Summary

High-Yield Exam Summary

References

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Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004;4(6 Suppl):190S-194S.
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.
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.
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.
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.
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