Spine

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Chapter 5

Spine

Francis H. Shen

Regional Anatomy and Surgical Intervals

Regional Anatomy

Osteology

Occiput (Fig. 5-1)

Foramen magnum

External occipital protuberance (inion)

• Thickest portion of bone (4-18 mm)

Supreme, superior, and inferior nuchal lines

Transverse sinus

Cervical Vertebrae (Fig. 5-2)

FIGURE 5-2 A, Superior view of atlas (C1), axis (C2), and C5 vertebrae.B, Top: An axial computed tomography (CT) scan of the atlas (C1) vertebra; its corresponding articulation to the dens (odontoid process) can be visualized at this level. Middle: An axial CT scan of the axis (C2) vertebra at the level of the pedicles. Bottom: An axial CT scan of the C5 vertebra at the level of the pedicles.

Arthrology

Cervical

Occipitocervical (Fig. 5-5)

• 50% of cervical flexion-extension

• Occipital condyles

• Ligamentum nuchae

• Tectorial membrane (after the foramen magnum it becomes the posterior longitudinal ligament)

• Anterior longitudinal ligament (continues throughout the mobile spine)

• Posterior occipitoatlantal and anterior occipitoatlantal ligaments

• One apical and two alar ligaments

FIGURE 5-5 A, The occipitocervical junction. Note the location and course of the vertebral artery. B, A lateral cervical radiograph. Notice the five vertebral lines: 1, prevertebral soft tissue line; 2, anterior vertebral line; 3, posterior vertebral line; 4, spinolaminar line; and 5, spinous process line. C, Midsagittal T1-weighted (left) and T2-weighted (right) magnetic resonance imaging scans of the cervical spine.

Atlantoaxial (Fig. 5-6)

• 50% of cervical rotation

• Transverse ligament

• Accessory ligament

• No intervertebral disc

FIGURE 5-6 A, Superior view of the atlantoaxial articulation. Note the relationship of the transverse ligament to C1-C2. B, An axial T2-weighted magnetic resonance imaging scan of the C1-C2 articulation. Notice the attachment of the transverse ligament (arrowheads) to C1 and its relationship to the odontoid process (*).

Uncovertebral joint (Fig. 5-7)

• Not a true diarthrodial joint

• Forms the anterior border of the neuroforamen

FIGURE 5-7 A lateral view of the subaxial cervical spine. Note the anatomic location of the uncovertebral joints and neuroforamen.

Facet joint

• Coronal alignment

• Shingled with the superior articular facet anterior to the inferior articular facet

Thoracic

Facet

• Coronal alignment

• Shingled with the superior articular facet anterior to the inferior articular facet

Costovertebral (Fig. 5-8)

• Rib articulates vertebra at body and transverse process

• Multiple ligamentous attachments

FIGURE 5-8 A, Lateral view of the thoracic spine. Note the relationship of the rib-vertebra articulation. B, A midsagittal T2-weighted magnetic resonance imaging scan of the thoracic spine.

Lumbar and Sacrum (Fig. 5-9)

Facet joint

• Sagittal alignment

• The superior articular facet lies lateral to the inferior articular facet

Sacroiliac joint

FIGURE 5-9 A, Lateral view of the lumbar spine. The superior articular process of the superior vertebra lies anterior to the inferior articular process of the inferior vertebra. B, A midsagittal T2-weighted magnetic resonance imaging (MRI) scan of the lumbar spine. C, A parasagittal T2-weighted MRI scan of the lumbar spine.

Muscles

Best grouped by region

• Cervical (Fig. 5-10)

FIGURE 5-10 Muscles of the anterior cervical spine.

• Thoracic (Fig. 5-11)

FIGURE 5-11 Muscles of the anterior thoracic spine.

• Lumbar (Fig. 5-12)

FIGURE 5-12 Muscles of the anterior lumbar spine.

Posterior

Best grouped by layers

• Superficial (Fig. 5-13, left half )

FIGURE 5-13 Superficial (left half) and intermediate (right half) musculature of the posterior spine.

• Intermediate (Fig. 5-13, right half )

• Deep (Fig. 5-14)

FIGURE 5-14 Deep musculature of the posterior spine.

Nervous System

Spinal Cord (Fig. 5-15)

Continuation of the medulla as it exits the foramen magnum

Terminates as the conus medullaris at T12-L1 or L2-L3

Continues caudally as the cauda equina

The spinal cord diameter is largest at the C6 vertebra

Three meninges: dura (outermost covering), arachnoid, and pia mater (innermost covering)

Cerebrospinal fluid is found between the arachnoid and pia mater

Dentate ligament (anchors the spinal cord in position)

FIGURE 5-15 Cross-sectional spinal cord anatomy with surrounding pia, arachnoid, and dura mater.

Gray Matter

Anterior/motor horn

• Somatomotor neurons

Intermediolateral horn

• Visceral center of gray matter

Posterior/sensory horn

• Somatosensory neurons

Sympathetic Chain

Cervical

• Posterior to the carotid sheath

• Lies anteriorly on the longus colli bilaterally

• Injury can result in Horner syndrome

• Ptosis

• Miosis

• Anhidrosis

Lumbar

• Typically, anterior to the psoas on the lateral aspect of the vertebral body

• Division results in a warm ipsilateral leg

Cross-Sectional Anatomy (Fig. 5-19)

Cervical spine cross section

Thoracic spine cross section

Lumbar spine cross section

FIGURE 5-19 A, Cross-sectional anatomy of the cervical, thoracic, and lumbar spine.B, An axial T2-weighted magnetic resonance imaging scan of the cervical spine at the level of the neuroforamen (top), thoracic spine at the level of the pedicle (left), and lumbar spine at the level of the pedicle (right).

Landmarks (Fig. 5-20)

Cervical Spine

Carotid tubercle (C6)

Sternal notch

Sternocleidomastoid muscle

Carotid pulse

Posterior

Inion

C2 spinous process

C7 spinous process

Thoracic Spine

Ribs

Sternal notch

Tip of scapula

Posterior

Ribs

Spinous processes

Lumbar and Lumbosacral Spine

Pubic symphysis

Pubic tubercle

Anterior superior iliac spine (ASIS)

Ribs

Posterior

Intercrestal line

Posterior superior iliac spine (PSIS)

Spinous processes

Approaches to the Spine

Anterior Approach to the Cervical Spine (Video 5-1)

Indications

Anterior Decompression of the Spinal Canal

Degenerative processes

Biopsy

Vertebral body

Disc space

Instrumentation

Anterior cervical placement

Positioning

Supine (Fig. 5-21)

Head position (Fig. 5-22)

• Typically, the head is placed in a neutral alignment

• Extension and contralateral head rotation can help improve surgical exposure if necessary

• Care should be taken to ensure that the degree of extension necessary is possible before intubation

• If the patient has any degree of myelopathy or neurologic changes with awake extension, an awake intubation should be considered

Position of arms

• At the patient’s side

• Gentle taping of the shoulders inferiorly can improve intraoperative radiographs

Additional tricks

• Neck extension can be facilitated by placement of a roll between the shoulder blades

• Gardner-Wells or Halter traction can be used if distraction is required

• Elevate the head of the operating table 30 degrees in the reverse Trendelenburg position to reduce venous bleeding

FIGURE 5-21 Supine positioning for surgery of the anterior cervical spine.

FIGURE 5-22 Relational anatomy of the anterior cervical spine.

Hazards

Neural Structures

Vascular

Carotid artery

• Runs in the medial aspect of the carotid sheath

Vertebral artery

• Typically enters the transverse foramen at the level of C6

• Ascends within the transverse foramen

• Can be at risk during resection of the uncovertebral joint

Epidural veins

Other

Trachea

Esophagus

Thoracic duct

Incision

Transverse Incision (Fig. 5-23)

In the skin crease along Langer’s lines

More cosmetic, but not extensile

FIGURE 5-23 Relationship of hyoid bone, thyroid cartilage, and cricoid cartilage to the level of the corresponding disc.

Longitudinal Incision

Just anterior to the sternocleidomastoid muscle

More extensile, but less cosmetically appealing

Superficial Dissection

Identify the platysma (Fig. 5-24)

• Divide the fibers of the platysma

• Alternatively, split the muscles of the platysma in line with fibers

• Elevate and mobilize the platysma superiorly and inferiorly as needed

FIGURE 5-24 Exposure of the platysma. SCM, Sternocleidomastoid.

Identify the anterior border of the sternocleidomastoid muscle (Fig. 5-25)

• Divide the fascia immediately anterior to the sternocleidomastoid muscle (deep cervical fascia)

FIGURE 5-25 Identify the anterior border of the sternocleidomastoid (SCM) and divide the deep cervical fascia.

Palpate the pulse of the carotid artery (Fig. 5-26)

• Divide the fascia immediately anterior to the carotid sheath (pretracheal fascia)

• Using blunt dissection, retract the sternocleidomastoid and carotid sheath (common carotid artery, internal jugular vein, and vagus nerve) laterally

• Retract the strap muscles (sternohyoid and sternothyroid) along with the trachea and esophagus medially

FIGURE 5-26 Palpate the pulse of the carotid artery within the carotid sheath and divide the pretracheal fascia. SCM, Sternocleidomastoid.

Continue with blunt dissection to develop the plane down to the anterior surface of the cervical vertebra (Fig. 5-27)

• Two arteries may be seen crossing the field from the carotid sheath toward the midline structures

• Superior thyroid artery

• Inferior thyroid artery

• One or both may have to be divided to increase surgical exposure

FIGURE 5-27 Identify the anterior cervical spine and longus colli. SCM, Sternocleidomastoid.

Deep Dissection

Deep dissection exposes the anterior cervical vertebra (Fig. 5-28)

• The longus colli muscles are now visible on either side

• The prevertebral fascia also can be seen covering the cervical vertebra

• The anterior longitudinal ligament can be seen as a gleaming white structure in the midline

• The sympathetic chain lies on the longus colli lateral to the vertebral bodies

Divide the prevertebral fascia

Detach and elevate the longus colli bilaterally for exposure

• At the level of the vertebral body, the anterior tubercle of the transverse process can help protect the vertebral artery

• Lateral dissection at the level of the disc should be performed carefully to reduce the risk of vertebral artery injury

Careful placement of the retractors deep to the longus colli reduces the risk of inadvertent injury to the surrounding structures

Closure

Hemostasis is achieved, and the deep structures are allowed to fall back into place

A deep drain can be placed based on the surgeon’s preference

The platysma, subcutaneous layer, and skin are closed in layers

Transoral Approach

Indications

Anterior decompression of the spinal canal at the atlantoaxial junction (tumor, infection, nonreducible/incompletely reduced symptomatic fracture, persistent symptomatic rheumatoid pannus, and congenital disorders); biopsy of the atlantoaxial junction

Positioning

Supine (Fig. 5-29)

Head Position

Typically neutral or slightly extended alignment

Care should be taken to ensure that the degree of extension necessary is possible before intubation

FIGURE 5-29 Patient positioning for the transoral approach to C1-C2. (Adapted from Winter RB, Lonstein JE, Denis F et al: Atlas of spine surgery, Philadelphia, 1995, WB Saunders.)

Intubation

Fiberoptic nasal intubation while the patient is awake

• Consider a preoperative tracheotomy

• Depending on the disease and the extent of exposure necessary

• If extensive manipulation of the tongue and palate is planned

Arms Positioned at the Patient’s Side

Taping of the shoulders inferiorly typically is not necessary for visualization of the C1-C2 junction

Additional Tricks

Consider application of skull tongs to stabilize the head or apply cranial traction if necessary

Elevate the head of the bed 20 to 30 degrees

• Reduces venous bleeding

• Reduces aspiration risk

Hazards (Figs. 5-30 and 5-31)

Neural Structures

Spinal cord

Hypoglossal nerve (Fig. 5-32)

• Particularly at risk when dissection entails lateral exposure greater than 15 mm from midline

FIGURE 5-30 An axial cross-sectional drawing of normal C1-C2 anatomy. Notice the relationship of the anterior tubercle of C1 to the dens of C2. Also notice the relationship of the transverse ligament to the dens and spinal cord. (Adapted from Winter RB, Lonstein JE, Denis F et al: Atlas of spine surgery, Philadelphia, 1995, WB Saunders.)

FIGURE 5-31 A sagittal drawing of normal C1-C2 anatomy. Notice that the tectorial membrane is the continuation of the posterior longitudinal ligament superiorly and lies posterior to the transverse ligament and anterior to the spinal cord. (Adapted from Vaccaro AR, Baron EM: Spine surgery, Philadelphia, 2008, WB Saunders.)

FIGURE 5-32 Surgical relationship of the hypoglossal nerve, vertebral artery, and internal carotid artery to C1-C2 vertebral bodies. (Adapted from Morrey BF, Morrey MC, editors: Relevant surgical exposures: master techniques in orthopaedic surgery, Philadelphia, 2007, Lippincott, Williams & Wilkins.)

Cerebrospinal Fluid (CSF) Leak

Primary closure is frequently not possible

Augment the repair with fibrin glue and sealant

Lumbar drains should be considered for persons with persistent leaks

Vascular

Vertebral artery (Fig. 5-33)

• At risk with lateral exposure greater than 20 mm from midline at the level of C1

• At risk with lateral exposure greater than 10 mm from midline at the level of the C2-C3 disc space

FIGURE 5-33 Surgical anatomy of the craniocervical junction. Notice that the vertebral artery lies just lateral to the C2-C3 disc space before entering into the transverse foramen of C1. (Adapted from Watkins RG: Surgical approaches to the spine, ed 2, New York, 2003, Springer.)

Internal carotid artery (Fig. 5-32)

• Particularly at risk when dissection entails lateral exposure greater than 15 mm from midline

Epidural veins

Mechanical Instability

Typically due to resection of the anterior ring of C1 and removal of the transverse ligament (see the Deep Dissection section, p. 196)

Consider preoperative or staged posterior C1-C2 fusion

Wound Infections

Consider preoperative cultures of the oropharynx and/or nares

Consider repeat intraoperative cultures

Other

Trachea

Esophagus

Dental

• Loose teeth should be addressed preoperatively

• Dental caries should be addressed to reduce wound infections

Eustachian tubes

Intraoperative/Preincision Preparation

Pack the upper esophagus and trachea with sterile gauze

• Minimizes the ingestion of blood and other products

• Reduces the risk of aspiration

Careful retractor placement improves visualization of the interdental gap (Fig. 5-34)

• Elevate the soft and hard palate

• A malleable self-retainer or a soft rubber catheter can be placed through each nostril looped around the uvula

• Depress the tongue

• A tongue blade retractor can be used

FIGURE 5-34 Retractor placement for the transoral approach to C1-C2. (Adapted from Albert TJ, Balderston RA, Northrup BE: Surgical approaches to the spine, Philadelphia, 1997, Saunders.)

Palpate the anterior tubercle of C1 in midline (Fig. 5-35)

• An intraoperative radiograph after positioning and prior to incision can help confirm the level and adequate exposure

• Confirm the location radiographically

FIGURE 5-35 Palpate the anterior ring of C1. A lateral radiograph can help confirm the level if necessary. (Adapted from Morrey BF, Morrey MC, editors: Relevant surgical exposures: master techniques in orthopaedic surgery, Philadelphia, 2007, Lippincott, Williams & Wilkins.)

Incision

A 1- to 2-cm vertical longitudinal midline incision (Fig. 5-36)

• Just proximal to the anterior C1 tubercle down onto the body of C2 distally

FIGURE 5-36 A vertical longitudinal midline incision. (Adapted from Albert TJ, Balderston RA, Northrup BE: Surgical approaches to the spine, Philadelphia, 1997, WB Saunders.)

Make an “H” incision (Fig. 5-37)

• Vertical limbs are placed as far lateral as possible

• Injury to the eustachian tubes can occur if the vertical limbs are too lateral

• Allows for two broad-based pharyngeal myomucosal flaps that are elevated superiorly and inferiorly

• The horizontal limb is based on the level of the soft palate

FIGURE 5-37 An “H” incision on the posterior pharyngeal wall with the horizontal limb at the level of the soft palate. (Adapted from Watkins RG: Surgical approaches to the spine, ed 2, New York, 2003, Springer.)

Superficial Dissection

Retract the Soft Palate (Fig. 5-38)

Simple retractor placement may be sufficient

The uvula may be sutured and retracted proximally

Divide the soft palate lateral to the uvula if necessary

• Place a suture and retract the uvula and soft palate

FIGURE 5-38 The soft palate divided with a curvilinear midline incision to help retract the soft palate and improve exposure. (Adapted from Watkins RG: Surgical approaches to the spine, ed 2, New York, 2003, Springer.)

Exposure of the Anterior Ring of C1 (Fig. 5-39)

Full-thickness subperiosteal dissection

• Divide the mucosa and pharyngeal musculature as one flap; four layers:

• Posterior pharyngeal mucosa

• Superior constrictor muscle of the pharynx

• Prevertebral fascia

• Anterior longitudinal ligament

• Attached to the anterior tubercle of C1

• May need to be sharply dissected free to maintain subperiosteal exposure

FIGURE 5-39 Subperiosteal dissection to expose the anterior tubercle of C1. (Adapted from Albert TJ, Balderston RA, Northrup BE: Surgical approaches to the spine, Philadelphia, 1997, WB Saunders.)

Exposure of the Lateral Mass of C1 (Fig. 5-40)

Elevate the longus colli muscles

Dissection laterally onto the midportion of the lateral mass of C1 bilaterally

• Excessive lateral dissection places neurovascular structures at risk (see the previous Hazards section)

• Maintaining midline orientation is imperative

• The anterior tubercle is an important landmark

• The midline can be distorted in patients with atlantoaxial rotatory subluxation

• Atlantoaxial rotatory subluxation can bring the vertebral arteries to the midline

FIGURE 5-40 The lateral mass of C1 exposed by subperiosteal dissection and elevation of the bilateral longus colli. (Adapted from Albert TJ, Balderston RA, Northrup BE: Surgical approaches to the spine, Philadelphia, 1997, WB Saunders.)

Exposure of the Body of C2 and the C1-C2 Joint (Fig. 5-41)

This exposure can be achieved during the superficial dissection along with exposure of the anterior tubercle of C1

Continue the dissection as far superiorly, inferiorly, and laterally as required for the pathologic condition being addressed

• Lateral dissection beyond the C1-C2 joint should be avoided

• Increases the risk for vertebral artery injury

FIGURE 5-41 Exposure of the anterior aspect of the C1-C2 joint. (Adapted from Winter RB, Lonstein JE, Denis F et al: Atlas of spine surgery, Philadelphia, 1995, WB Saunders.)

Deep Dissection

Exposure of C2

Exposure of the odontoid process of C2 (Fig. 5-42)

• Remove the central 1.0 to 1.5 cm of the anterior tubercle of C1

• Perform with a burr, pituitary rongeur, and/or curettes

• Exposure of the lateral shoulder of the odontoid process and/or the medial aspect of lateral masses are visualized

• Maintaining midline orientation is imperative

• The anterior tubercle is an important landmark

• Maintaining the anatomic midline orientation can be difficult after resection of the anterior ring of C1

FIGURE 5-42 Removal of the anterior tubercle of C1. (Adapted from Winter RB, Lonstein JE, Denis F et al: Atlas of spine surgery, Philadelphia, 1995, WB Saunders.)

Expose the Transverse Ligament (Fig. 5-43)

Preserve the transverse ligament if possible

• Occipitocervical instability can occur if the anterior ring of C1 and the transverse ligament have been resected

Removal of the transverse ligament

• The presence of pannus or tumor may require deliberate or inadvertent removal of the transverse ligament

• If the transverse ligament is resected or if it is incompetent, then posterior C1-C2 fusion should be considered

• As a result, residual pannus or tumor may need to be left in place

Closure

Confirm that no CSF leak has occurred

• Use the intraoperative Valsalva maneuver

• Persistent leaks may require a lumbar drain

If possible, reapproximate the longus colli in the midline

Approximate the pharyngeal layer with resorbable suture

If a “H”-type incision was used, close the horizontal limb first, followed by the vertical limb

Approximate the soft palate in layers with absorbable suture

Anterior Transthoracic Approach to the Thoracic Spine (Video 5-2)

Indications

Anterior Spinal Cord Decompression

Correction of Deformity

Anterior release for scoliosis or kyphosis

Other Indications

Fusion for instability or deformity

Biopsy

Positioning

Lateral decubitus position with the side to be approached oriented up (Fig. 5-44)

• For deformity, the convexity of the curve is typically oriented up

• For decompressions, the side with the greatest stenosis to be addressed is typically oriented up

FIGURE 5-44 Lateral decubitus position. (Photo courtesy Vincent Arlet, MD.)

Secure the patient firmly to the operating table

• Stabilize the patient with either beanbags or hip positioners

• Carefully note the orientation of the spine before draping

• Noting the orientation reduces the risk of disorientation and inadvertent entry into the spinal canal

• Noting the orientation is particularly important if rotation of the table is required intraoperatively

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Spine

Regional Anatomy

Occiput (Fig. 5-1)

Cervical Vertebrae (Fig. 5-2)

Thoracic Vertebrae (Fig. 5-3)

Lumbar Vertebrae (Fig. 5-4)

Sacrum

Arthrology

Thoracic

Lumbar and Sacrum (Fig. 5-9)

Muscles

Posterior

Nervous System

Spinal Cord (Fig. 5-15)

Gray Matter

White Matter

Nerve Roots

Sympathetic Chain

Surgical Intervals

Vascularity (Fig. 5-18)

Thoracic

Lumbar and Lumbosacral

Spinal Cord

Cross-Sectional Anatomy (Fig. 5-19)

Landmarks (Fig. 5-20)

Posterior

Thoracic Spine

Posterior

Lumbar and Lumbosacral Spine

Posterior

Anterior Approach to the Cervical Spine (Video 5-1)

Biopsy

Instrumentation

Positioning

Supine (Fig. 5-21)

Hazards

Vascular

Other

Incision

Transverse Incision (Fig. 5-23)

Longitudinal Incision

Superficial Dissection

Deep Dissection

Closure

Transoral Approach

Positioning

Supine (Fig. 5-29)

Intubation

Arms Positioned at the Patient’s Side

Additional Tricks

Hazards (Figs. 5-30 and 5-31)

Cerebrospinal Fluid (CSF) Leak

Vascular

Mechanical Instability

Wound Infections

Other

Intraoperative/Preincision Preparation

Incision

Superficial Dissection

Retract the Soft Palate (Fig. 5-38)

Exposure of the Anterior Ring of C1 (Fig. 5-39)

Exposure of the Lateral Mass of C1 (Fig. 5-40)

Exposure of the Body of C2 and the C1-C2 Joint (Fig. 5-41)

Deep Dissection

Removal of the Odontoid Process (Fig. 5-43)

Expose the Transverse Ligament (Fig. 5-43)

Closure

Anterior Transthoracic Approach to the Thoracic Spine (Video 5-2)

Correction of Deformity

Other Indications

Positioning

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