Anterior cervical discectomy and fusion

Hi,

Sharing a draft of a chapter that we wrote for a surgical atlas which never saw the light of day. If you do it differently, or have any comments, please share in the comment box below. Warning – this blog post has 50 odd images and will take a while to load. Here goes –

1.  Introduction

Anterior cervical discectomy and fusion (ACDF) was described over half a century ago by Smith and Robinson in 1955 and Ralph Cloward in 1958. This procedure has stood the test of time and is frequently used to treat cervical spine pathologies with good outcomes when used for the correct indications.

2.  Indications

Chapter ACDF Atlas KEYNOTE.003a copyFigure 1: C5-6 disc herniation causing severe, unresolving radiculopathy in the left upper extremity

  1. Cervical radiculopathy (intractable, recurrent or progressive)
  2. Cervical myelopathy (moderate to severe or progressive)
  3. Specific types of cervical trauma, tumors, or infections were spinal cord decompression and anterior column reconstruction is required.

3.  Contraindications

  1. Posterior spinal cord compression
  2. Anterior spinal compression dorsal to the vertebral body
  3. Bleeding disorder

4.  Preoperative planning

Plain radiographs and MRI are essential. CT myelography may be performed if MRI is contraindicated.

5.  Equipment and instruments

  1. C-arm fluoroscopy
  2. Loupe magnification with headlight or microscope
  3. Neuro drill (3 mm diamond burr)
  4. Radiolucent operating table (traction pulley and weight optional)

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Figure 2: Mayo table instruments – 1) Pituitary forceps, 2) Decker pituitary forceps, 3) Kerrison punch 1 mm, 4) Kerrison punch 2 mm, 5) Weitlaner retracotrs, 6) Lempert rongeur, 7) Smith Peterson rongeur 8) Cloward blade retractors, 9) Appendiceal retractors, 10) Freer periosteal elevator, 11) Nerve hook, 12) Penfield four, 14) Pair of skin hooks, 14) Plain forceps, 15) Cushing’s neuro forceps (toothed), 16) Bayonet forceps, 17) Metzenbaum scissors, 18) 15 blade on long handle, 19) 21 blade (skin knife), 20) Needle holder, 21-23) Artery forceps, 24) Mixter forceps, 25) Pair of Kittner dissectors (peanut sponges), 26) Bone trephine (optional, for iliac crest bone graft), 27) Fazier suction tips, 28) Mallet, 29) Bone tamp, 30) Periosteal elevator, 31) Bayonetted backward 3-0 angled curette, 32) Bayonetted forward 3-0 angled curette, 33) Bayonetted forward 3-0 straight curette, 34) Bone wax, 35) Gelfoam, 36) Cottonoids

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Figure 3: Back table: Self retaining retractor set and Caspar distractor set

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Figure 4: Back table with implants and its instrumentation. 1) Locking plates, 2) Variable angle & fixed angle screws, 3) Plate bender, 4) Awl, 5) Drill bit, 6) Tap, 7) Drill guide, 8) Plate holder, 9) Screw driver, 10) Temporary fixation pins and its holder, 11) Rasps, 12) Cage holder, 13) Tamp, 14) Screw driver, 15) Mallet

6.  Positioning

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Figure 5: Positioning of the patient. 1) Nasogastric tube: The tube can be palpated on exposure and can be used to identify the esophagus. Postoperatively, it can be used for feeding if the patient develops severe dysphagia. This is optional for one-level ACDF but recommended for multilevel ACDF 2) Head ring. 3) Shoulders are taped down so that the lower cervical spine can be visualised on lateral fluoroscopy. Care should be taken to avoid excessive pressure so as not to injury the brachial plexus. 4) Shoulder pad is inserted at the level of the scapula so that the neck can be placed in slight extension. 5) A sand bag can be placed underneath the iliac crest if bone graft harvest is planned. 6) The arms are wrapped around a bed sheet that is tucked underneath the body. A slight reverse Trendelenburg position is given to reduce venous congestion. Optional – a) Gardner Wells traction: It is can be useful if intraoperative traction is desired. Usually for one or two level ACDF this is not mandatory if Casper distractor system is used. b) Neuromonitoring: This may be useful in patients with spinal cord compression and myelopathy. It is mandatory to record baseline readings before positioning the patient as sometimes signals may be lost if patient is placed in excessive traction or hyperextension.

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Figure 6: Surface landmarks with there approximate vertebral levels: 1) Hyoid bone (C2-3), 2) Laryngeal prominence (Adam’s apple) of the thyroid cartilage (C4-5), 3) Cricoid cartilage (C6), 4) Sternal notch, 5) Clavicle, 6) Chassaignac’s tubercle (C6) can be palpated in patients with thin necks, 7) Anterior border of the sternocleidomastoid (SCM) muscle (dashed line)

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Figure 7: Positioning of the c-arm for lateral fluoroscopy. The table is translucent for X-rays and hence AP fluoroscopy is also possible.

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Figure 8: radiopaque instrument such as a artery forceps can be used to mark the skin level of the incision as well as to confirm if the intended levels of fusion (C5-6 & C6-7) are visualised on lateral fluoroscopy.

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Figure 9: Draping the patient. The cervical spine and the iliac crest is kept exposed. Left sided approach is chosen because the surgeon is left-handed. A right-sided approach is more convenient for a right-handed surgeon. The rate of recurrent laryngeal nerve injury is similar regardless of the side that is chosen.  We prefer a left sided approach for low cervical approaches (below C6) to avoid the recurrent laryngeal nerve which can have a higher and irregular course on the right side. Routine preoperative antibiotics (Cefuroxime) are given as prophylaxis. 10 mg of Dexamethasone is given to reduce postoperative edema and the risk of dysphagia.

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Figure 10: 1) Bipolar electrocautery, 2) Protected monopolar electrocautery, 3) Diamond burr 3mm, 4) Frazier suction tip

7.  Anterior cervical spine exposure

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Figure 11: Following a subcutaneous infiltration using 1:2,00,000 adrenaline solution, a transverse incision is made along the Langer’s lines up to the anterior border of the sternocleidomastoid (SCM) muscle. As a C5-6 and C6-7 ACDF is planned the incision is approximately at the level of the cricoid cartilage (★). Multiple levels can be accessed via a long transverse incision and unsightly longitudinal incisions are not required. (H – head end, F – foot end. In all subsequent images the right side is cephalad and left is caudad end with the surgeon standing on the left side of the patient)

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Figure 12: The subcutaneous layer contains the platysma, identified as longitudinally running muscle fibres. The platysma is divided in the line of the incision using monopolar electrocautery.

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Figure 13: The platysma muscle is undermined cephalad and caudad. The subplatysmal areolar tissue can be dissected using a electrocautery or using Metzenbaum scissors. Superficial veins if encountered can be  cauterised if they cross the surgical field. The goal is to expose the anterior border of the SCM longitudinally.

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Figure 14: Ethilon 2-0 stay sutures are used to convert the transverse incision into a longitudinal access along the anterior border of SCM. Thus a long enough transverse incision after undermining the platysma can give access to the entire length of the anterior border of SCM obviating the need for a longitudinal skin incision.

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Figure 15: The investing layer of the deep cervical fascia is dissected to identify the loose areolar tissue that lies medial to the SCM. Care is to be taken not to enter the fascia covering the SCM.

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Figure 16: The interfascial dissection proceeds, the SCM (▼) can be retracted laterally. Strap muscles (▲) can be seen covering the trachea.

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Figure 17: Blood vessels may be seen crossing the surgical plane. They can either be ligated using 3-0 Mersilk if large, or can be coagulated using a bipolar if thin and small. Middle thyroid vein and transverse branches of the deep ansa cervicalis are encountered in a deeper plane can be sacrificed.

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Figure 18: At the C6 level the superior belly of omohyoid muscle (*) is seen. Red line (superior border of omohyoid muscle). Blunt dissection can performed to mobilise this muscle can it can be retracted along with the trachea medially. Alternatively, the omohyoid muscle can be divided if wider and longer exposure is required.

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Figure 19: Next step is to palpate for the internal carotid artery to help identify the plane of dissection. This surgical plane between the viscera (trachea and oesophagus) and carotid sheath (ICA, internal jugular and vagus nerve) contains loose areolar tissue and can be easily dissected bluntly using a finger or two Kittner dissectors (peanut sponges).

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Figure 20: Once prevertebral fascia is dissected discs can be identified as small “hills” and vertebral bodies as “valleys”. A Cloward retractor (or a Langenback retractor) can be used to retract the visceral structures medially. (1 – disc, 2 – longus colli, 3 – carotid sheath, 4 – SCM). Typically, an extra level should be exposed so that tension on the viscera is minimal. Avoid performing surgery through a small exposure. In this case where a 2-level ACDF is planned one should have enough exposure to perform a 2-level corpectomy. This reduces the pressure of retraction on the esophagus and results in minimal or no dysphagia postoperatively.

Note: Structures crossing this surgical plane. Mid cervical levels – (C4-C6) Middle thyroid vein. Upper cervical levels C3 and above – Superior thyroid vein & artery may need ligation. Care should be taken to avoid injury to superior laryngeal nerve at lies close to the superior thyroid artery. Lower cervical levels (C7-T2) – Inferior thyroid artery. Care should be taken to avoid injury to the recurrent laryngeal nerve, especially on the right side where it can have a higher and more transverse course.

8.  Discectomy

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Figure 23: The C6 anterior tubercle (Chassaignac’s tubercle) is palpated to judge the level. (★ – Longus colli)

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Figure 24: A prebent (two right angle bends) 18-gauge spinal needle is inserted into the disc space and the level confirmed using a c-arm.

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Figure 25: Confirmation of the C5-6 level using a prebent spinal needle.

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Figure 26: The C5-6 disc is marked with electrocautery and the needle is removed. (★ – Longus colli). The midline is judged by the medial borders of the longus colli.

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Figure 27: The right sided longus colli (★) muscle is elevated off the anterior surface of the vertebral body and the disc using a bovie taking care to stay subperiosteal to avoid damage to the oesophagus. Note that the suction tip is being used as a retractor. There are no blood vessels over the disc, however, bleeding can be encountered from nutrient foramina that at usually located at mid body level. Care is to be taken not to dissect superficial to the longus muscle as it can injure the sympathetic chain.

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Figure 28: Similarly, the left longus colli muscle (★) is elevated off. Bilaterally, the longus should be elevated right upto the uncovertebral joint (dotted white line) at the disc level and up to a point where the bone surface starts to curve posteriorly at the vertebral body level. Remember that the vertebral body is unprotected at the disc level as it not in the bony neuroforamen and any further lateral dissection can endanger the vessel. Adequate elevation of the longus colli not only allows for proper positioning of the self-retaining retractors but also allows for adequate exposure for anterior foraminotomy or uncinectomy.

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Figure 29: Depth of the wound is measured using a colour coded depth gauge. Usually the blade on the visceral side is longer than the one that retracts the carotid sheath.

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Figure 30: Self-retaining retractors (Symmetry®) are used to expose the anterior surface of the spine. Wide elevation of the longus colli muscle is mandatory as shown in Figure 24 and 25). This helps to anchor the blades firmly and prevents herniation of the muscle and esophagus from underneath the blade. The visceral blade (red) is usually longer and has a smooth edge. Notice that the handle of the visceral retractor is not removed. This is because there is a tendency of the retractor to move laterally due to the push by the trachea and esophagus. The weight of the handle as well can its control by the assistant can ensure that the retractor remains steady.

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Figure 31: The annulus of the disc is then incised using a 15-number blade on a long handle taking care to always point the sharp end of the blade towards the midline. Anterior osteophytes if any can be removed using a rongeur.

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Figure 32: The disc material is then scrapped off the endplates using combination of curettes and pituitary forceps.

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Figure 33: The disc once cleared looks like a smile. The uncovertebral joints are clearly defined as it helps to determine the midline more accurately.

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Figure 34: The orientation of the endplates and the midline is used to insert the Casper distractor pins. If the disc is kyphotic, the pins can be inserted divergently so that on distraction lordosis can be restored.

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Figure 35: Casper distractor is applied to distract the disc space gently. The posterior annulus can now be seen clearly.

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Figure 36: Lateral fluoroscopic view showing the Casper pins and distracted disc space.

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Figure 37: Once the posterior annulus is removed, the vertical fibres of the PLL can be visualised. To facilitate this exposure a corse 3 mm diamond burr may be used to thin down the posterior edge, especially if there are extensive osteophytes.

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Figure 38: PLL takedown (midline method). Frequently a midline cleft in the PLL can be identified. Using a 15 number blade the PLL can be incised over a nerve hook as it elevates the PLL off the dura.

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Figure 39: Sometimes the plane can be found on the lateral edge of the PLL as seen here. Similarly, a nerve hook can be used to elevate the PLL off the dura and then incised using a 15 number blade.

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Figure 40: Once the PLL is removed a glistening white dura can be seen (★).

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Figure 41: PLL takedown is not mandatory in all situations. We prefer to perform in patients with disc ruptures when we suspect herniation of disc fragments behind the PLL. Here the dura can be visualised well (★). A Gelfoam (▲) is placed to control foramina epidural bleeding that can be frequently encountered after effective foraminal decompression.

9.  Fusion

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Figure 42: Endplates are prepared (decorticated) using a 3 mm coarse diamond burr. The aim to flatten out the endplates so that the smile-shaped disc space can be converted into a rectangular box. A nerve hook can then be used to measure the depth of the endplate.

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Figure 43: An appropriately sized rasp maybe used to decorticate the endplates.

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Figure 44: A sizer then can be used to determine the graft or the cage size. It is important to release the distraction on the Casper pins and then assess the “fit” of the sizer taking care not to over distract the disc space.(null)

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Figure 45: A lateral fluoroscopic view shows the 6 mm sizer in situ.

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Figure 46: In this patient two level discectomy was performed. Lateral fluoroscopy shows C5-6 and C6-7 ACDF using PEEK cages(null)

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Figure 47: A lateral fluoroscopy view shows the PEEK cages and their position

10.  Anterior Cervical Plating

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Figure 48: The size of the plate selected is such that the upper and the lower screw holes are just above and below their respective endplates. A fixation pin in inserted in the C6 body as shown (▶︎).

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Figure 49: A lateral fluoroscopy view shows that the size of the plate is appropriate and the edges of the plate are at least 5 mm away from the adjacent normal disc spaces. If the plate is too long it can lead to adjacent segment disease.

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Figure 50: The screws are then placed in the remaining holes of the plate. We have used self-drilling and self-tapping screws. The depth measurement of the disc space performed previously is used to determine the length of the screws. The screws used in this case are variable-angle, unicortical screws which allow for slight settling of the disc Fixed-angle screws do not allow for such settling and may be used in patients with significant instability, such as trauma.

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Figure 51: Finally, all the screw are locked into the plated. In this particular plate (Atlantis, Medtronic), the gold coloured screw is turned 90º so that it covers the variable-angled bone screws (green).

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Figure 52: Final lateral and AP fluoroscopy view show the position of the plate and the screws.(null)

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Figure 53: Prior to closure always inspect the viscera, especially the esophagus. A 10 size drain is placed in the prevertebral area. The closure is performed in two layers. Platysma is closed with interrupted sutures using 2-0 Vicryl. Subcuticular closure of the skin is done using 3-0 Monocryl.

11.  Postoperative care and rehabilitation

  • Head elevation
  • Airway and Oxygen saturation monitoring for 4-6 hrs
  • Neurological examination q 4 hours
  • Sip test after 6 hours with clear liquid and straw for dysphagia then advance diet as tolerated to soft diet and solids
  • Drain is typically removed on postoperative day 1 if the drain output is less than 20 cc.
  • X-ray cervical spine AP/Lateral are done before discharge
  • Patient is discharge on post-operative day 1 or 2, if no dysphagia.

12.  Complications

  • Dysphagia is the most common complication. It is usually temporary, but in about 1% it could be permanent.
  • Injury to the superior laryngeal nerve (loss of pitch) or the recurrent laryngeal nerve (hoarseness one voice)
  • Injury to esophagus (due sharp dissection, retractor blade, cautery or drill)
  • Injury to carotid artery, internal jugular vein or the vagus nerve
  • Injury to vertebral artery: due to far lateral dissection beyond the uncovertebral joints or injury to anomalous course of vertebral artery
  • Horner’s syndrome: Injury to the sympathetic chain that overlies the longus colli
  • Neurological deficit due to cord or root injury / edema during surgery or post-operatively due to dislodgement or misplaced interbody graft/ implants, epidural hematoma
  • CSF leak
  • Airway obstruction (prevertebral edema or hematoma)
  • Wound infection
  • Implant failure or graft dislodgement
  • Nonunion (higher risk in smokers, diabetics and in multilevel discectomies)

 

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