ACDF - Anterior Cervical Discectomy and Fusion

Anterior cervical discectomy and fusion (ACDF) is one of the most commonly performed spinal procedures. Robinson and Smith described it in 1955, and it changed cervical spine surgery by giving anterior access for neural decompression.

How it developed. The milestones:

• 1955 - Smith and Robinson describe the anterior approach with an iliac crest graft
• 1958 - Cloward describes the cylindrical dowel graft technique
• 1970s-80s - anterior cervical plating
• 1990s-2000s - cage technology
• 2000s-present - total disc replacement as an alternative

Who needs it. Cervical radiculopathy that has failed conservative treatment, any progressive or significant cervical myelopathy, and symptomatic disc herniation, soft or hard. ACDF also serves traumatic or degenerative cervical instability and tumour or infection of the anterior column. Axial neck pain on its own is not an indication; it needs correlating instability.

Where. The levels operated mirror the pattern of degenerative disease:

• C5-6 - 55-65%
• C6-7 - 25-30%
• C4-5 - 5-10%
• C3-4 - rare

The route to the disc passes between the carotid sheath laterally and the trachea and oesophagus medially. What follows is the anatomy in the order it is met.

The layers. Skin and platysma, then the superficial cervical fascia, with the medial border of sternocleidomastoid as the lateral landmark. Deep to it the carotid sheath (carotid artery, internal jugular vein, vagus nerve) is retracted laterally while the trachea and oesophagus, the oesophagus lying behind the trachea, are retracted together medially. The pretracheal fascia is divided to reach the spine, where the longus colli muscles cover the anterior vertebral bodies.

The disc space. From front to back:

• Anterior longitudinal ligament
• Annulus fibrosus
• Nucleus pulposus
• Posterior longitudinal ligament
• Uncovertebral joints (joints of Luschka) at the lateral margin

Longus colli and what lies beyond it. The muscle is elevated as far as the uncovertebral joints, and no further, because the vertebral artery and the sympathetic chain lie lateral to it. The sympathetic chain sits lateral on longus colli, and injuring it produces a Horner syndrome.

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The recurrent laryngeal nerve. It supplies all the intrinsic laryngeal muscles except cricothyroid, so injury causes hoarseness and aspiration. On the left it loops around the aortic arch and ascends in the tracheo-oesophageal groove, a longer and more constant protected course; on the right it loops around the subclavian artery, runs more obliquely, is more variable and more vulnerable, and is non-recurrent in about 1 in 200.

Which side. The classic teaching is a left-sided approach to protect the nerve, and a slight leftward deviation of the oesophagus helps access from that side; the thoracic duct is on the left but is at risk only below C7, which is rarely relevant. The comparative evidence does not confirm the anatomical argument: in Beutler's 328 procedures there were 5 injuries after left-sided and 4 after right-sided approaches, no association with side. Surgeon familiarity and the side of the pathology are legitimate reasons to go right, and some surgeons prefer the right for a better angle to right-sided pathology.

The superior laryngeal nerve. Its external branch supplies cricothyroid and is at risk with retraction above C3. Injury affects voice quality and projection.

History. Axial neck pain, dermatomal arm pain with numbness or tingling, and myotomal weakness point to a root. Hand clumsiness and gait disturbance point to the cord, and bladder or bowel symptoms mark severe myelopathy. Record the duration, the progression and the response to conservative treatment.

Examination. Radiculopathy is examined root by root, and the findings should agree with the level on the MRI:

Myelopathy signs. Look for upper motor neuron signs:

• Hyperreflexia, clonus and a Babinski response
• Lhermitte sign - an electric shock down the spine with neck flexion
• Hoffmann sign - thumb and index flexion when the middle fingertip is flicked
• A broad-based, spastic gait
• Hand dysfunction on the grip-and-release test
• Inverted radial reflex

What else it could be. Neck and arm symptoms have mimics from the brain to the wrist, and the table gives the discriminator for each:

MRI is the gold standard. T1-weighted images show the anatomy and bone marrow changes, T2-weighted images show cord signal (myelomalacia) and disc pathology, and gradient echo (T2*) reduces metal artefact and shows the disc better. It demonstrates the soft disc herniation, the osteophyte complex of the hard disc, cord compression, foraminal stenosis and any signal change within the cord, which is a poor prognostic sign. The MRI findings must correlate with the clinical findings to confirm the surgical level.

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CT gives the bone detail: bone quality, OPLL, trauma, and the cage and plate sizing before surgery. CT myelography is the substitute when MRI is contraindicated (pacemaker, claustrophobia); it is sometimes better than MRI for foraminal stenosis, at the price of a lumbar puncture.

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Plain radiographs. AP, lateral and oblique views, with flexion-extension views when instability is suspected. Look for disc space narrowing, osteophytes, foraminal narrowing on the obliques and the alignment (lordosis or kyphosis); the dynamic views can reveal instability not seen on static imaging.

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Electrodiagnostics. EMG and nerve conduction studies help when the level is unclear, to separate radiculopathy from a peripheral neuropathy, as a baseline before surgery, and when a brachial plexopathy is suspected. Radiculopathy shows fibrillations and positive sharp waves with reduced motor unit recruitment, and these changes take 2-3 weeks to develop.

Radiculopathy without myelopathy. The natural history is generally favourable: 50-70% improve with conservative treatment, so an adequate trial of 6-12 weeks comes first unless there is a progressive deficit. The trial draws on:

• Medications - NSAIDs, a short course of oral corticosteroids in the acute phase, neuropathic agents (gabapentin, pregabalin), muscle relaxants
• Physiotherapy - strengthening exercises, postural training, activity modification, and cervical traction, which remains controversial
• Injections - cervical epidural steroid injection or selective nerve root block, by a transforaminal or interlaminar route

Myelopathy. Cord compression with long tract signs goes to early surgical referral without a conservative trial, because progression may be irreversible.

When conservative care fails. Confirm that the clinical picture matches the imaging, then plan the operation. ACDF is the workhorse for 1-3 levels of anterior cervical pathology; beyond that, consider the alternatives, chosen on the pathology and the patient:

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Most of the common complications are transient; the permanent ones are rare but serious:

Dysphagia is the most common complication, and patients want "usually resolves" quantified. Prospective swallowing assessment in 249 patients found dysphagia in 50.2% at 1 month, 32.2% at 2 months, 17.8% at 6 months and 12.5% at 12 months: near-universal early, halved by two months, and still noticed by a residual minority at a year. What makes that tolerable to hear is the severity split, since only 4.8% had moderate or severe dysphagia at 6 months. Female sex and multilevel surgery were the risk factors, so warn those patients more firmly; vocal-cord paresis persisted in 1.3% at 12 months (prospective longitudinal study, Level II).

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Haematoma causing airway obstruction is a surgical emergency. Most present within 24-48 hours; the bedside response is set out under Postoperative Care.

Oesophageal injury is very rare (0.02-0.25%) and may present late, and if it is missed the result is mediastinitis. Treatment is nil by mouth, antibiotics, and repair or diversion.

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Vertebral artery injury is very rare and produces massive bleeding, controlled with packing and intervention. Spinal cord injury is rare with careful technique, may occur during dissection of OPLL, and is devastating.

Late problems declare themselves at follow-up:

• Graft or cage - subsidence, dislodgement (anterior or posterior) requiring revision, pseudarthrosis
• Hardware - screw loosening or pullout, plate malposition
• Persistent symptoms - wrong-level surgery, inadequate decompression, recurrent stenosis
• Adjacent segment disease, which may require extension of the fusion

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Adjacent segment disease needs a cumulative number rather than an annual one. Across 374 patients and 409 arthrodeses followed for up to 21 years, symptomatic adjacent-segment disease developed at a relatively constant 2.9% per year, and Kaplan-Meier survivorship predicted 25.6%, roughly one in four, within 10 years; two-thirds of those affected ultimately needed further surgery, and the risk was highest at C5-6 and C6-7. This is the cervical spine's own figure, not an extrapolation from lumbar data.

The risk pattern inverts the natural assumption: single-level fusion carried a higher adjacent-level risk than multilevel fusion. The likely explanation is selection, since the levels left unfused after a single-level procedure are often already degenerate, whereas a multilevel fusion has already incorporated them. The corollary is not to fuse more levels; it is to include all symptomatic degenerate levels rather than leave a marginal one out, and to consider a motion-preserving option in suitable candidates. Disc replacement does reduce it, on Level I data: in a 599-patient randomised FDA IDE trial followed to 7 years, adjacent-level secondary surgery ran at 4.4% with two-level TDR against 11.3% with ACDF, and index-level reoperation at 4.4% against 16.2%, though the trial was industry-sponsored and restricted to carefully selected patients without facet arthrosis, kyphosis or instability.

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The first 48 hours are critical for haematoma detection. Monitor the airway, run neurological checks, manage pain, and screen for dysphagia before oral intake; a soft collar is optional, for 2-6 weeks if used, and mobilisation is early. Three findings are red flags:

• Increasing neck swelling
• Stridor or respiratory distress
• A new neurological deficit

If airway compromise is developing, open the wound at the bedside to decompress it. Emergency intubation may be needed and can be very difficult or impossible, and the patient returns to theatre for evacuation once the airway is secure.

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Recovery. Most patients return to sedentary work within 2-4 weeks:

ACDF has excellent outcomes for radiculopathy; myelopathy outcomes depend on severity and duration:

What predicts the result. Duration, pathology, the state of the cord, the number of levels and the patient:

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ACDF is one of the most frequently performed spine operations worldwide and is a core procedure in fellowship curricula worldwide. Evidence and recommendations are drawn from international guidelines and registries to give a global picture rather than any single country's practice.

Global epidemiology

• Cervical radiculopathy has an annual incidence of roughly 80-100 per 100,000, peaking in the fifth and sixth decades; the great majority improve with non-operative care.
• Degenerative cervical myelopathy is the commonest cause of non-traumatic spinal cord dysfunction in adults worldwide, and its prevalence is rising with ageing populations.
• C5-6 and C6-7 are consistently the most commonly operated levels across all regions, mirroring the distribution of degenerative load.

Major guidelines, side by side

Registry and outcome evidence

• FDA IDE randomised trials (Mobi-C, Prestige, ProDisc-C, Bryan) underpin the global acceptance of cervical arthroplasty as non-inferior to ACDF for selected 1-2 level disease, with lower index-level reoperation in long-term follow-up.
• Spine registries and large administrative datasets (for example the Quality Outcomes Database in North America and national spine registries in Europe and Australasia) consistently report high patient-reported improvement and low major-complication rates after ACDF, supporting its status as a workhorse procedure.

High- vs limited-resource practice variation

• In well-resourced settings, PEEK/titanium cages, anterior plating, intra-operative fluoroscopy and (increasingly) arthroplasty are routine.
• In limited-resource settings, structural allograft or autograft (Smith-Robinson tricortical iliac crest) without a plate remains a valid, low-cost technique with good single-level fusion rates; intra-operative imaging and disc replacement may be unavailable.
• Across all settings the principles are identical: confirm clinico-radiological correlation, decompress adequately, restore disc height and alignment, and do not delay surgery for progressive myelopathy.

These are high-yield discussion points where an examiner probes judgement rather than recall - state both sides and where the evidence currently sits.