Anterior cervical discectomy and fusion (ACDF)

Anterior cervical discectomy and fusion (ACDF) is a commonly performed spinal fusion procedure for the decompression of the cervical cord due to disc protrusions and posteriorly projecting osteophytes.

It is not to be confused with an ACDA (anterior cervical disc arthroplasty).

Indications

• spondylosis or disc herniation of the cervical spine, resulting in myelopathy/radiculopathy that is unresponsive to conservative therapy 
• certain malignant, traumatic or infective processes of the cervical vertebrae resulting in instability ^{5, 6}

Contraindications

•  anatomical variants of the vertebral artery ⁶

Procedure

Positioning

Patients are placed in a supine position with the neck in a neutral position ⁵. 

Technique

The procedure is carried out via an anterolateral neck incision with surgical approach passing between the aerodigestive tract (trachea, oesophagus, pharyngeal muscles) medially and the carotid neurovascular bundle (carotid artery, internal jugular vein, vagus nerve) laterally ².

The intervertebral disc is then resected along with the fibrocartilage covering the adjacent vertebral endplates (to allow for eventual osseous fusion). It is possible to reach back to the posterior longitudinal ligament, removing osteophytes and disc protrusion as well and extending laterally to decompress the neural exit foramina ^1,2. 

Once decompression has taken place an interbody spacer (or "cage") of some kind is introduced to assist fusion/improve stability. This can be in the form of ^1,3: 

• bone
  • autogenous bone graft (e.g. from the anterior iliac crest of the patient harvested at the same time as the fusion is performed)
  • allogenic bone graft (e.g. from cadaveric iliac bone or fibula)
  • animal allogenic bone graft (e.g. bovine or calf)
• synthetic usually packed with cancellous autobone, demineralized bone matrix or ceramics
  • plastic
  • metal (e.g. titanium or stainless steel)
  • ceramic 

Following this, a plate with screws that pass into the vertebral bodies above and below the operative segment is usually introduced to provide additional stabilisation ¹.

Newer devices combine screw fixation and interbody spaced into the one device, fitting entirely within the interbody space without the added bulk of the anterior plate ¹. 

Follow-up

A common way to follow up ACDF is the lateral cervical radiograph to assess for prevertebral soft tissue swelling. A 2017 prospective study with 106 patients post-ACDF ⁴ measured the difference of the soft tissue thickness anterior to the midportion of C3 and C6 at immediate post-op, 2 weeks, 1 month, 6 months and 12 months after surgery against baseline:

• C3: significant difference up to 1 month; from third month the difference was not significant (i.e. back to the baseline)
  • post-op: 5.10-6.56 mm
  • 2 weeks: 2.61-4.07 mm
  • 1 month: 1.12-2.68 mm
• C6: significant up to 6 months
  • post-op: 4.01-5.47 mm
  • 2 weeks: 2.72-4.18 mm
  • 1 month: 1.78-3.24 mm
  • 3 months: 0.98-2.44 mm
  • 6 months: 0.40-1.86 mm

Complications

Although the procedure is generally safe a number of complications can be encountered including ³: 

• intraoperative complications
  • oesophageal perforation
  • damage to the carotid artery or internal jugular vein
• immediate postoperative complications
  • dysphagia due to plate and screws
  • hoarse voice due to damage to the recurrent laryngeal nerve
• delayed complications
  • adjacent segment degeneration
  • adjacent level ossification