John Heflin and John M. Rhee
GENERAL CONSIDERATIONS
Anterior Approach (Smith-Robinson)
The approach chosen depends on a number of factors, including the spinal segments that must be exposed, the nature of the procedure to be performed, and the patient's body habitus.
In general, the Smith-Robinson approach allows access from C2 down to T1 in most patients. However, local variations in patient morphology may either limit or increase the extent of available exposure.
Ease of access to the C2-3 disc depends on the location of the mandible and can be assessed on the preoperative lateral radiograph.
Nasal intubation is preferable when approaching this level as it allows the mandible to be maximally closed, away from the line of sight of the disc.
Depending on the location of the mandible with respect to C3-4, nasal intubation may be preferable in certain instances of C3-4 access as well.
For pathology at C7-T1 or distal, careful scrutiny of the disc space with respect to the sternal notch on lateral radiographs will help to assess whether a sternal-splitting approach may be necessary.
In some patients with long necks, access to T2 or even T3 may be possible with a standard Smith-Robinson approach.
In those with short or stocky necks, even getting to C7 may be a challenge (FIG 1).
Imaging studies should be evaluated for anatomic variations such as medial aberrancy of the vertebral artery.
FIG 1 • Long versus short necks. A. In patients with long necks, anterior exposure through a standard Smith-Robinson approach readily provides far distal access (eg, down to T1-2 disc space [arrow]). B. In those with short necks, however, even getting to C6-7 may be difficult if the sternum blocks the necessary trajectory to the disc space (arrow), although it can almost always be done.
Considerable debate exists as to whether the “sidedness” of approach affects the rate of postoperative superior laryngeal nerve palsy. The literature is not conclusive but suggests higher rates with right-sided approaches.
If a patient has had prior neck surgery and it is desirable to approach the spine from the opposite side to avoid scar, a preoperative indirect laryngoscopy should be performed by ear, nose, and throat (ENT) consultation to rule out a recurrent laryngeal nerve palsy.
If one exists, the spine must be approached from the side of the injury to avoid the possibility of bilateral vocal cord palsy. If one does not exist, the spine can be approached from either side.
Lateral Retropharyngeal Approach (Whitesides)
This approach can be used for anterior access to the upper cervical spine but not the basiocciput.
It is often used for high cervical bony lesions, including tumors or infections for which a posterior approach is not possible, unstable fractures or dislocations with deficient or incompetent posterior elements, or posterior nonunions (particularly for fusions of C1 to C2).
It is also useful for access to high cervical ventral or ventrolateral intradural lesions such as neurofibromas or meningiomas.
It allows unilateral access to C1 to C3. Access to the far contralateral side requires a second approach.
Potential complications include injury to the spinal accessory nerve and the vertebral artery. The jugular vein also lies within the operative field and can be a site of significant bleeding if inadvertently injured.
Significant retropharyngeal swelling has occurred and can result in prolongation of intubation if the patient's airway becomes obstructed.
Anterior Approach to the Cervicothoracic Junction (Transmanubrial-Transclavicular Approach)
There are several different approaches for exposing the cervicothoracic junction, including the transmanubrial-transclavicular and the sternal-splitting (median sternotomy) approaches.
The sternal-splitting (median sternotomy) approach may be useful in providing improved distal access to the upper thoracic spine.
Deep dissection is essentially the same for the two approaches.
Cranial to caudal dissection is recommended to avoid injury to the major crossing vessels distally (eg, the left brachiocephalic vein).
With a left-sided approach, the thoracic duct is at greater risk. It passes into the left venous angle between the subclavian artery and the common carotid artery.
With a right-sided approach, the recurrent laryngeal nerve is at greater risk because of its greater variability versus the left side, where the nerve is more constant in its location in the tracheoesophageal groove.
POSITIONING
Anterior Approach (Smith-Robinson)
The patient is positioned supine with the neck slightly extended.
The amount of extension tolerated by the patient without developing neurologic symptoms should be assessed preoperatively and not exceeded during positioning (FIG 2).
A bump (eg, rolled sheets) under the shoulders facilitates gentle extension of the spine.
A halter or Garner-Wells tong is optional but not routinely necessary for anterior cervical discectomy and fusion (ACDF) surgery.
FIG 2 • Positioning. Especially in patients with myelopathy, the amount of preoperative extension tolerated without worsening of neurologic symptoms should be assessed and never exceeded during positioning. A rolled sheet is placed under the scapulae to help gently extend the neck.
A foam doughnut is placed behind the occiput to prevent pressure necrosis.
The head is placed in neutral rotation. Doing so provides landmarks (the nose and the sternal notch) that are in line with the longitudinal axis of the spine for orientation during decompression and instrumentation.
Depending on the relationship of the mandible to the upper cervical spine, proximal approaches to C2-3 may be easier if the head is gently rotated away from the side of the approach.
The amount of rotation should be kept in mind to prevent disorientation during surgery.
The shoulders are gently taped down to facilitate intraoperative radiographic visualization.
Excessive force should be avoided when taping down the shoulders to avoid brachial plexus injuries.
Spinal cord monitoring (eg, somatosensory evoked potentials [SSEP] and motor evoked potentials [MEP]) can be used to help prevent positioning-related nerve injuries, but it is not completely sensitive in detecting injury.
Lateral Retropharyngeal Approach (Whitesides)
The patient is placed supine with the head turned away from the side from which the approach will be performed unless the patient is constrained in a halo for instability reasons.
If this is the case, the exposure will be more challenging but still possible.
Nasotracheal intubation opposite the side of the approach is desirable as it allows the jaw to be fully closed, offering the least inhibited exposure.
The pinna (earlobe) can be retracted forward and sewn anteriorly to allow better access to the styloid process and posterior ear area.
The entire cervical region and lower face is prepared and draped.
TECHNIQUES
ANTERIOR APPROACH (SMITH-ROBINSON)
Incision and Superficial Dissection
A transverse incision placed in a skin crease is more cosmetic and suffices for accessing up to three disc levels in most instances.
A longitudinal incision, although less cosmetic, allows for a more extensile approach (C2-thoracic spine) and should be considered when three or more discs require access, or if the patient has a very thick, muscular neck.
The incision is made using palpable anterior structures as a guide (ie, C3 hyoid bone, C4-5 thyroid cartilage, C6 carotid tubercle, C7 cricoid cartilage) (TECH FIG 1A).
The preoperative lateral radiograph can also be used to determine roughly where to make the incision to allow optimal access to the desired disc(s).
The surgeon should try to make the incision such that it will be in line with the “line of sight” of the intended disc space (TECH FIG 1B).
Transverse incisions may extend from the anterior two thirds of the sternocleidomastoid (SCM) to beyond the midline.
Longer incisions and greater tissue mobilization facilitate multilevel procedures and will heal with a nearly imperceptible scar if placed within a natural skin crease.
Vertical incisions, if used, are placed along the medial border of the SCM.
The incision is continued through the subcutaneous fat to the platysma (TECH FIG 1C).
The platysma is divided in line with the skin incision using electrocautery.
Blunt dissection with scissors undermines the edges of the platysma.
This allows for greater mobilization of the soft tissues, which is helpful in accessing multiple disc levels and getting enough exposure to place plates and screws.
Superficial veins crossing the field of dissection may need to be ligated to facilitate exposure (TECH FIG 1D).
TECH FIG 1 • Incision. A. The location of the incision is determined by palpating for known landmarks. Generally, these landmarks overlie specific vertebrae or disc spaces, such as the hyoid bone (C3), thyroid cartilage (C4-5), cricoid cartilage (C7), and carotid tubercle (C6). B. Alternatively, by looking at the preoperative lateral radiograph, one can estimate the optimal location for the skin incision. (Top arrow indicates the C4-5 approach, bottom arrow the C5–7 approach.) C. The incision is continued through the subcutaneous fat to the platysma. Platysma fibers are cut in line with the incision. D. The surgeon should avoid injuring crossing structures when possible. Superficial veins crossing the field of dissection may need to be ligated to facilitate exposure, however.
Deep Dissection
The anterior border of the SCM is identified.
Blunt dissection is then carried through the deep cervical fascia directly medial to the SCM.
The SCM is retracted laterally to allow palpation and identification of the carotid artery (TECH FIG 2A).
The carotid artery should be visualized and will form the lateral border of the approach; the esophagus will define the medial border of the approach.
Once the carotid is identified, a plane through the pretracheal fascia lying between the carotid sheath and the medial structures (thyroid gland, trachea, and esophagus) is created (TECH FIG 2B).
Finger dissection in this plane is useful in allowing extensile exposure.
TECH FIG 2 • A. The sternocleidomastoid is retracted laterally using blunt retractors. This will allow palpation and identification of the carotid artery. B. After the carotid artery is identified, a plane is created between the carotid sheath and the medial structures (thyroid gland, trachea, and esophagus). Blunt dissection techniques are most effective in developing this plane.
Extending the Exposure
If surgery involves one level, minimal mobilization may be necessary. If the surgery involves multiple levels or the skin incision is not collinear with the desired disc space, greater mobilization is helpful.
In general, crossing structures should be preserved if possible to avoid potential injury to neural structures (eg, laryngeal nerves). Blunt dissection with scissors, Kittners, or fingers works best.
The superior thyroid vessels typically overlie C3-4, and the inferior thyroid vessels generally overlie C6-7.
The omohyoid is encountered crossing distal-lateral to cephalad-medial in the interval medial to the sternomastoid at roughly the C6 level. It can be divided with electrocautery or left intact.
Dividing the omohyoid will allow for a more extensile cephalad-caudal exposure and less tension on the wound for easier placement of plates and screws in multilevel or very distal constructs.
Elevation of Longus Colli and Identification of Levels
Using bipolar electrocautery, subperiosteal elevation of the longus colli should be done to the level of the uncinate processes bilaterally, and at least from the midportion of the vertebral body above to the midportion of the body below the level for which discectomy is planned (TECH FIG 3A).
Time and care spent on carefully elevating the longus colli facilitates proper, stable placement of self-retaining retractors, which in turn facilitates decompression and accurate placement of hardware.
Retractor blades are then placed beneath the elevated longus colli (TECH FIG 3B).
Careful placement of retractors will help avoid injury to the esophagus and sympathetic chain (which runs along the ventral surface of the longus colli).
TECHNIQUES FIGURE 3C represents a cross-sectional view at the C5 level demonstrating the plane of dissection for the Smith-Robinson approach.
Location of the appropriate level should be ensured by intraoperative radiographs before disruption of the disc.
TECH FIG 3 • A. Bipolar electrocautery is used to elevate the longus colli in a subperiosteal fashion to the level of the uncinate processes bilaterally. B. Self-retaining retractors can be placed beneath the elevated longus colli to allow an unimpeded view of the anterior spine. Care should be taken to avoid injuring the esophagus and sympathetic chain during placement of the retractors. The use of cephalad/caudal retractors is optimal but not necessary in most cases. C. A cross-sectional view through the neck at C5 demonstrating the plane of dissection.
LATERAL RETROPHARYNGEAL APPROACH (WHITESIDES)
Incision and Superficial Dissection
A transverse incision is extended from the mastoid tip, posterior to the ear, and is carried along the inferior border of the mandible, preferably in a natural skin crease.
The incision is then directed caudally along the anterior border of the SCM (TECH FIG 4A).
This incision can be extended as needed according to the amount of distal cervical spine exposure required. It can be carried as far as the sternal notch.
The incision is then carried through the subcutaneous tissues and platysma muscle using electrocautery.
Dissection is carried out using blunt dissection techniques in the subplatysmal plane, allowing the creation of superior-anterior and inferior-posterior musculocutaneous flaps (TECH FIG 4B).
The superior-anterior flap is elevated to the inferior border of the parotid gland.
The greater auricular nerve is identified and dissected out of the subcutaneous tissue both caudally
TECH FIG 4 • A. A transverse incision is extended from the mastoid tip and is carried along the inferior border of the mandible, turning caudally and continuing along the anterior border of the sternocleidomastoid muscle. B. The incision is carried through the subcutaneous tissues and platysma muscle using electrocautery in line with the incision. Subplatysmal flaps are developed with blunt dissection techniques to allow adequate mobilization of tissue. C. The greater auricular nerve is identified and mobilized from the subcutaneous tissues to allow adequate retraction. It is sometimes necessary to sacrifice the greater auricular nerve. This will result in a small area of insensate skin but otherwise has no functional significance. D. The external jugular vein and collaterals are mobilized or ligated as needed. The sternocleidomastoid is mobilized anteriorly with the carotid sheath. For additional exposure the sternocleidomastoid can be taken down from the mastoid prominence by sectioning through the tendinous insertion.
and cephalad to allow adequate retraction (TECH FIG 4C).
It is occasionally necessary to sacrifice the greater auricular nerve; this will leave the patient with a small insensate patch of skin but no long-term functional deficit.
The external jugular vein is identified and then mobilized or ligated as needed (TECH FIG 4D).
The SCM is mobilized and retracted medially and anteriorly with the carotid sheath.
Mobilization of Sternocleidomastoid
Depending on the amount of exposure required, the SCM may be detached partially or entirely from its tendinous insertion at the mastoid prominence.
Be sure to leave enough tissue cuff to allow reapproximation of the muscle on closure.
Take care to identify and protect the spinal accessory nerve, which enters the SCM about 3 cm distal to the tip of the mastoid process.
For limited exposure, the spinal accessory nerve can be retracted anteromedially with the SCM (TECH FIG 5).
For more extensive exposure, it can be dissected off the jugular foramen in a cephalad direction and retracted posterolaterally while the SCM is everted.
Deep Dissection
Lymph nodes found in the field of dissection and around the spinal accessory nerve can be excised.
The lateral process of C1 is now easily palpable about 1 cm distal to the mastoid process.
The interval between the jugular vein and the longus capitis muscles is then created, allowing access to the retropharyngeal space.
The retropharyngeal space can be opened further with blunt dissection techniques employing scissors, Kittners, or fingers.
A sharp elevator or bipolar electrocautery can then be used to elevate the longus capitis and longus colli muscles from the transverse processes and lateral masses of C1 and C2 (TECH FIG 6A).
Retraction is best accomplished by bending a malleable retractor so that it can be used as a lever against the contralateral transverse process, thus elevating the soft tissues anteriorly and medially (TECH FIG 6B).
TECH FIG 5 • The spinal accessory nerve is identified as it enters the sternocleidomastoid about 3 cm distal to the tip of the mastoid process and retracted anteriorly with the sternocleidomastoid. The lateral process of C1 will lie essentially in the middle of the field of dissection, about 1 cm distal to the mastoid process.
TECH FIG 6 • A. Bipolar electrocautery can be used to elevate the longus capitis and longus colli muscles subperiosteally from the transverse processes and lateral masses of C1 and C2. B. Plane of dissection for the retropharyngeal approach. For deep retraction, a malleable retractor can be used as a lever against the contralateral transverse process, allowing elevation of the soft tissues anteriorly and medially.
ANTERIOR APPROACH TO THE CERVICOTHORACIC JUNCTION (TRANSMANUBRIAL-TRANSCLAVICULAR APPROACH)
Incision and Superficial Dissection
A standard Smith-Robinson approach is taken, with the incision extended distally over the manubrium (TECH FIG 7A).
The sternal and clavicular heads of the SCM are released at the tendinous attachments and retracted proximally and laterally. Be sure to leave enough tissue cuff to allow reapproximation of the muscle on closure.
Likewise, the sternohyoid and sternothyroid are sectioned and retracted proximally and medially (TECH FIG 7B).
The omohyoid is also generally sectioned for better exposure. It does not need to be repaired.
Mobilization of Clavicle
The medial third of the clavicle and the left side of the manubrium is then cleared of any remaining soft tissue.
The clavicle is then divided (typically with a Gigli saw) at the junction of the medial and middle thirds (TECH FIG 8A).
Care must be taken to avoid injuring the left subclavian vein, which is normally closely apposed to the undersurface of the clavicle.
At this point, the medial third of the clavicle can be disarticulated from the manubrium (TECH FIG 8B).
If more exposure is needed, the left side of the manubrium can be removed in a piecemeal fashion by a rongeur.
Alternatively, the medial third of the clavicle and a section of the manubrium can be removed together by careful sectioning. This will allow plate or wire reconstruction of the clavicle and manubrium if desired.
If the manubrium and medial third of the clavicle are removed in this manner, the sternal head of the SCM can be left in continuity with the manubrium and reflected en bloc (TECH FIG 8C).
Deep Dissection
The inferior thyroid vein and artery are often encountered with deeper dissection and may need to be ligated for better exposure.
Careful blunt dissection proceeds in the same interval as for the standard Smith-Robinson approach (ie, between the carotid sheath laterally and the trachea and esophagus medially).
The recurrent laryngeal nerve is almost always found between the esophagus and trachea on the left side of the neck within this plane.
Blunt retractors are then placed and the carotid sheath, left brachiocephalic artery, and innominate vein are retracted inferolaterally (TECH FIG 9A).
Likewise, a blunt retractor is used to retract the trachea, esophagus, left recurrent laryngeal nerve, and right brachiocephalic vessels inferolaterally to the patient's right.
The prevertebral fascia is then identified and incised to expose the vertebral bodies. Once adequately dissected, the surgeon can visualize and access as far distally as T3 or T4.
TECHNIQUES FIGURE 9B represents a cross-sectional view at the cervicothoracic junction demonstrating the plane of dissection for the transmanubrial-transclavicular approach.
At the completion of the procedure, the clavicle is replaced and plated.
TECH FIG 7 • A. The incision for a low Smith-Robinson approach can be extended along the anterior border of the sternocleidomastoid to the midsagittal plane at roughly the sternal notch and then extended vertically to just beyond the manubrial–sternal junction. B. The sternal and clavicular heads of the sternocleidomastoid are released and reflected laterally while the sternohyoid and sternothyroid muscles are sectioned and reflected medially. The omohyoid is usually released during the exposure. It does not need to be repaired.
TECH FIG 8 • A. The clavicle is divided at the junction of the medial and middle thirds, taking care to avoid injuring the left subclavian vein, which is normally closely apposed to the undersurface of the clavicle. B. The medial third of the clavicle can be disarticulated from the manubrium at the manubrioclavicular joint. This will generally provide adequate exposure to the C7-T1 level. C. For additional exposure, the left side of the manubrium can be removed piecemeal using a rongeur. A second option involves careful sectioning of the manubrium, which will allow lateral reflection of both the manubrium and medial third of the clavicle without disarticulation of the manubrioclavicular joint.
TECH FIG 9 • A. Blunt retractors are used to carefully retract the carotid sheath, left brachiocephalic artery, and innominate vein inferolaterally, while the trachea, esophagus, left recurrent laryngeal nerve, and right brachiocephalic vessels are retracted inferomedially. B. Cross-sectional view through the cervicothoracic junction demonstrating the plane of dissection for the transmanubrial-transclavicular approach.