The Spine

The posterior approach can be undertaken with the patient in either of two positions:

For both positions, use a cold-light headlamp to illuminate the deepest layers around the spine.

The internervous plane lies between the two paraspinal
muscles (erector spinae), each of which receives a segmental nerve
supply from the posterior primary rami of the lumbar nerves.

Deepen the incision through fat and fascia in line with
the skin incision until the spinous process itself is reached. Detach
the paraspinal muscles subperiosteally as one unit from the bone, using
a dissector, such as a Cobb elevator, or with cautery (Fig. 6-3).
Dissect down the spinous process and along the lamina to the facet
joint. In a young patient, the tip of the spinous process is a
cartilaginous apophysis; it can be split in the midline, making
subperiosteal muscle removal easier (Fig. 6-4).

If necessary, dissection can be continued laterally,
stripping the facet joint capsule from the descending and ascending
facets. To do this, strip the joint capsule in a medial to lateral
direction across the posterior aspect of the descending facet; then,
continue over the tip of the mamillary process of the more lateral
ascending facet. If the transverse processes must be reached, continue
dissecting down the lateral side of the ascending facet and onto the
transverse process itself (see Fig. 6-4).

Close to the facet joints, in the area between the
transverse processes, are the vessels supplying the paraspinal muscles
on a segmental basis. These branches of the lumbar vessels frequently
bleed as the dissection is carried out laterally. Vigorous
cauterization of these

vessels
may be necessary to stop the bleeding. Note that the posterior primary
rami of the lumbar nerves, which also supply the paraspinal muscles
segmentally, run with these vessels. Loss of some of these nerves does
not totally denervate the paraspinal muscles, because they are
innervated segmentally (see Fig. 6-4).

Remove the ligamentum flavum by cutting its attachments
to the superior, or leading, edge of the inferior lamina using either a
curette or sharp dissection. Immediately beneath are epidural fat and
the blue-white dura. Using blunt dissection and staying lateral to the
dura, carefully continue down to the floor of the spinal canal,
retracting the dura and its nerve root medially (Figs. 6-5, 6-6, 6-7 and 6-8).

Place the patient in the prone position on a radiolucent table, with the abdomen free and the extremities padded.

Palpate the spinous processes to identify the midline. Fluoroscopy is used to determined the disc level.

The approach splits the fibers of the erector spinae muscle group that are innervated segmentally.

The skin, subcutaneous adipose tissue, and the erector spinae fascia are sharply divided with a knife.

The erector spinae muscle fibers are split by the
dilating/retracting tube and abutted against the lamina and medial
facet joint.⁷ The distal lamina and
ligamentum flavum are resected on the affected side to expose the nerve
root over the disc. Some of the medial facet can be resected to
decompress the lateral recess. The nerve root is then retracted
medially to expose the pathologic disc (Fig. 6-9).

Meticulous positioning of the retractors must be done
with landmarks and fluoroscopy because a very small incision is made.
Any deviation from the planned course may make it difficult to find the
pathology. If the incision is too medial, the spinous processes may
impede the proper positioning of the retracting tube. A tube that is
angled excessively will make it difficult to work and target the
microscope. This can be mitigated by using a tilting operating table.
Meticulous hemostasis is important, as the small access port can be
obscured easily by excessive bleeding.

The tube/retractor can be repositioned or angled
differently to address pathologies in different locations, for example,
to access a sequestered disc, a far lateral disc, or to decompress a
contralateral spinal stenosis. Larger tubes are available if more
exposure is required. In the lordotic spine, a small change in the
angle of the tube can permit access to an adjacent level.

The muscles of the lumbar spine are made up of
superficial and deep layers. The superficial layer consists of the
latissimus dorsi, a powerful muscle of the posterior axillary wall that
originates from the spinous processes and inserts into the
intertubercular groove of the humerus. The surgically important deep
layer consists of the paraspinal muscles and itself is divided into two
layers: the superficial portion, which contains the sacrospinalis
muscles (erector spinae), and the deep portion, which consists of the
multifidus and rotator muscles (Fig. 6-10).

This arrangement is not apparent during surgery, because the approach involves detaching all these muscles in a single mass.

The dorsal lumbar fascia and the supraspinous (supraspinal) ligaments lie between the skin and the

spinous processes. The fascia is a broad, relatively thick, white sheet
of tissue that forms a sheath for the sacrospinalis muscles and
attaches to the spinous processes (see Fig. 6-10).
It extends to the cervical spine, where it becomes continuous with the
nuchal fascia of the neck. Medially, it is attached to the spinous
processes of the vertebrae, the supraspinous ligaments, and the medial
crest of the sacrum. Inferiorly, it is attached to the iliac crests.
Laterally, it is continuous with the origin of the aponeurosis of the
transversus abdominis and latissimus dorsi muscles.

The supraspinous ligaments extend from vertebra to
vertebra, connecting the spinous processes. They blend intimately with
the attachment of the dorsal lumbar fascia to the spinous processes (Fig. 6-14).

Further dissection consists of detaching the two layers
of muscle from bone. Because these muscles are detached in a single
mass, their critical feature, in regard to their surgical anatomy, lies
in their blood supply and not in their structure. The segmental lumbar
vessels branch directly from the aorta. They wrap around the waist of
each vertebral body and then ascend close to the pedicle, where they
divide into two branches. One supplies the spinal cord; the other,
larger branch then comes directly posteriorly to supply the paraspinal
musculature. During the approach, these vessels appear between the
transverse processes, close to the facet joints (see Fig. 6-11).
They often bleed as dissection is carried out. In addition, the
arteries branch within the muscle bodies, frequently creating a very
vascular field. For this reason, the dissection should be kept as close
to the midline as possible; no major vessels cross the midline, and the
plane is safe for use (Fig. 6-13; see Fig. 6-11).

The ligamentum flavum is the most important structure in
the deep layer. Consisting of yellow elastic tissue, the ligament takes
origin from the leading edge of the lower lamina and inserts into the
anterior surface of the lamina above, about halfway up onto a small
ridge (Fig. 6-12). The two ligamenta flava, one
from each side, meet in the midline, but generally do not fuse; the
plane between the ligamentum flavum and the underlying dura fat can be
entered most easily at that point. Because of its attachments, the
ligamentum flavum is removed best from the leading edge of the lower
lamina through sharp dissection or curettage (see Fig. 6-5A).

The major danger in the deep dissection involves damage
to the dura. Once the ligamentum flavum is entered, a thin spatula
should be placed beneath it to protect the underlying dura from being
torn (see Fig. 6-6A). The cord itself and the
nerve roots often are difficult to see as a result of bleeding from
epidural veins. The veins, which are thin-walled and easy to rupture,
even with blunt dissection, can be controlled by direct pressure using
a pattie or by bipolar cautery.

Place the patient supine on the operating table (see Fig. 6-14).
Make sure that two areas remain bare for incision: one for the
abdominal incision, and one for harvesting an anterior iliac crest bone
graft. Insert a urinary catheter to keep the bladder empty. Use of
mechanical calf compression is recommended to decrease the risk of
thromboembolism.

The midline plane lies between the abdominal muscles on
each side, segmentally supplied by branches from the seventh to the
12th intercostal nerves. Therefore, this incision can be extended from
the xiphisternum to the pubic symphysis.

Deepen the wound in line with the skin incision by
cutting through the fat to reach the fibrous rectus sheath. Incise the
sheath longitudinally, beginning in the lower half of the incision, to
reveal the two rectus abdominis muscles (Fig. 6-16). Separate the muscles with the fingers to expose the peritoneum (Fig. 6-17).
Then, pick up the peritoneum carefully between two pairs of forceps
and, after making sure that no viscera are trapped beneath it, incise
it with a scissors (Fig. 6-18). Extend the
incision distally, but take care not to incise the dome of the bladder
at the inferior end of the wound. With one hand inside the abdominal
cavity to protect the viscera, carefully deepen the upper half of the
incision, staying in the midline and cutting through the linea alba,
the band of fibrous tissue that separates the two rectus abdominis
muscles in the upper half of the abdomen. Complete the exposure by
cutting through the peritoneum in the upper half of the wound (Fig. 6-19).

Use a self-retaining Balfour retractor to retract the rectus abdominis muscles laterally and the bladder distally (Fig. 6-20).
Perform a routine abdominal exploration. Next, put the operating table
in Trendelenburg’s position at 30° and carefully pack the bowel

in
a cephalad position, keeping it inside the abdominal cavity. Spread a
moist lap pad (swab) over it to prevent loops of bowel from slipping
free. It is much safer to keep the bowel within the abdominal cavity,
but do not pack it so tightly that vascular compromise is induced. In
women, the uterus may be retracted forward with a 0 silk suture placed
in its fundus and tied to the Balfour retractor.

Infiltrate the tissue over the anterior surface of the
sacral promontory with a few milliliters of saline solution to make
dissection easier and to allow identification of the presacral
parasympathetic nerves that run down through this area. For the L5-S1
disc space, incise the posterior peritoneum in the midline over the
sacral promontory. The sacral artery runs down along the anterior
surface of the sacrum and must be ligated or clipped. The ureters
should be well lateral to the surgical approach.

Preserve any small nerve fibers that are found. Identify
the L5-S1 disc space either by palpating its sharp angle or by
inserting a metallic marker and taking a radiograph. The L5-S1 disc
space lies below the bifurcation of the aorta; it should be possible to
expose it fully without mobilizing any of the great vessels (Figs. 6-21 and 6-22).

Operating on the L4-5 disc space requires a larger
exposure; mobilizing the great vessels is necessary, unless the
vascular bifurcation occurs much higher. Carefully incise the
peritoneum at the base of the sigmoid colon and mobilize the colon
upward and to the right to expose the bifurcation of the aorta, the
left common iliac artery and vein, and the left ureter. Identify the
aorta just above its bifurcation and gently begin blunt dissection on
its left side. Identify and ligate the fourth and fifth left lumbar
vessels, then divide them. Now, the aorta, vena cava, and left common
iliac vessels can be moved to the right, exposing the L4-5 disc space.
This exposure is difficult to achieve; a high incidence of venous
thrombosis has been reported with anterior surgery at this level. Take
care not to injure the left ureter, which crosses the left common iliac
vessels roughly over the sacroiliac joint. The ureter may have to be
moved laterally, but mobilize it only as much as necessary to reduce
the risk of postoperative ischemic stricture formation.

An alternative method is to approach the L4-5 disc space
from below, working upward into the apex of the vascular bifurcation.
Isolate the left and right common iliac artery, placing umbilicus loops
around them. Retract the two arteries cephalad and laterally

to
expose the common iliac veins. Dissect into the confluence of the veins
and isolate the left common iliac vein with a loop. Gently retract the
venous structures to expose the disc space. Use only minimal retraction
to avoid injuring the intima, which may lead to venous thrombosis (see Fig. 6-22).

Position the patient lying flat and supine on a radiolucent table.

The landmark for access to the L5-S1 disc is usually
distal to the midway mark between the umbilicus and symphysis. A more
distal incision is required for the L5-S1 disc because of its downward
orientation. The L4-5 disc is generally located a few centimeters from
the umbilicus, and the incision is made directly over the disc. L3-4 is
a few centimeters proximal to the umbilicus and is also approached with
an incision directly over it. The incisions can be transverse if only
one level is done or the more versatile incision for one or more level
is a midline longitudinal or slight oblique incision (Fig. 6-23).¹³

An interval just medial to the rectus abdominus and under the rectus is developed. The rectus is innervated segmentally.

Continue the incision to the ventral rectus fascia (Fig. 6-24). The rectus fascia is cut longitudinally on the medial edge of the muscle (Fig. 6-25). The medial edge is identified, and the rectus is lifted up and retracted to expose the dorsal fascia and the arcuate line (Fig. 6-26).
The inferior epigastric vessels are identified and preserved. Blunt
dissection is used to develop a plane dorsal to the rectus abdominis
and toward the lower quadrant. If exposing proximal to L5, the fascia
of the arcuate line is divided (Fig. 6-27).

Continuing the blunt dissection toward the left lower
quadrant, retroperitoneal fat is eventually encountered; underneath it,
the psoas muscle can be seen. At this point, branches of the
genitofemoral nerve are readily identified lying on the psoas and just
medial is the common iliac artery. Retractors appropriate to the
direction of the incision and size should be determined (Fig. 6-28).
The ureter is generally seen on the underside of the peritoneum. The
peritoneum and ureter are retracted medially and the common iliac vein
is seen just dorsal to the artery and crossing from proximal-lateral to
distal-medial. Caution must be used not to damage the thin walls of the
vein, as it is easily the most fragile structure of this approach. The
soft tissues in front of the L5-S1 disc and sacral promontory are
bluntly pushed medially to expose the middle sacral vein(s) (Fig. 6-29).
The veins require clipping, cauterizing, and ligating to divide them
and mobilize the left iliac vein. To expose the L4-5 disc, the
dissection is moved proximal to the iliac vessels. A plane between

the
psoas and the iliac vessels is developed bluntly. The ascending
iliolumbar vein should be identified and ligated/clipped before
retracting the iliac vein.¹⁴

The retroperitoneal approach can expose from the distal
aspect of T11 to S1. Exposing more proximal discs requires control and
division of the segmental vessels to mobilize the aorta and vena cava.

The anterior approach to the lumbar spine involves three
stages of dissection. The superficial stage consists of cutting the
skin and subcutaneous tissues down to the bowel. Below the skin lies
the linea alba, a fibrous structure in the midline that is identified
most easily in the upper abdomen. Cutting the linea alba in the lower
half of the abdomen exposes the rectus muscle, which can be separated
by finger pressure. Beneath it is the posterior rectus sheath and
peritoneum.

The anatomy of the intermediate stage, which involves
packing away the bowel, is the anatomy of the bowel and is not included
in this book.

The deep stage of dissection consists of mobilizing the
retroperitoneal structures that lie anterior to the L4-5 and L5-S1 disc
spaces. These structures include the aorta, vena cava, common iliac
vessels, lumbar vessels, ureter, and presacral plexus.

The long, flat rectus abdominis muscle extends along the
length of the entire abdomen, split into two muscles in the upper half
by the linea alba. The muscle is enclosed in a fascial sheath. Above
the umbilicus, the sheath has three elements: the aponeurosis of the
internal oblique splits to enclose the rectus muscle; the aponeurosis
of the external oblique passes in front of the rectus to form part of
the anterior sheath; and the aponeurosis of the transversus abdominis
fascia passes behind to form part of the posterior sheath. The inferior
margin of the posterior sheath is known as the semicircular line
(semicircular fold of Douglas). Below the umbilicus, all three
aponeuroses pass anteriorly, leaving a thin film of tissue posteriorly (Figs. 6-31 and 6-32).

The arrangement of the rectus sheath and the linea alba
means that, in the upper half of the incision, the approach through
fibrous tissue leads directly down to the peritoneum, whereas in the
lower half, it leads to the rectus abdominis muscle. Because of this,
it is easier to open the abdomen in the lower half of the incision (Fig. 6-33; see Fig. 6-32).

The inferior epigastric artery supplies blood to the
lower half of the rectus abdominis muscle. The artery lies between the
muscle and the posterior part of the rectus sheath. If the surgical
plane remains in the midline, this vessel should escape injury. If the
artery is damaged when the rectus muscle is mobilized, it can be tied
with impunity.

Deep surgical dissection consists of freeing the distal
ends of the aorta and the vena cava from the vertebrae in the L4-5
vertebral area. The aorta divides on the anterior surface of the L4
vertebra into the two common iliac arteries. Just below this
bifurcation, the common iliac vessels divide in turn at about the S1
level into the internal and external iliac vessels. The internal iliac
is the more medial of the two (Fig. 6-34).

The aorta and vena cava are held firmly onto the
anterior parts of the lower lumbar vertebrae by the lumbar vessels.
These segmental vessels must be mobilized to permit the aorta and vena
cava to be moved (see Fig. 6-13). Because the
arterial structures are easier to dissect and more muscular than are
the thin-walled venous structures, the preferred approach to the L4-5
disc space is from the left, the more arterial side. The median sacral
artery originates from the aorta at its bifurcation at L4 and runs in
the midline, over the sacral promontory and down into the hollow of the
sacrum (see Fig. 6-34). The lumbosacral disc
usually lies in the V that is formed by the two common iliac vessels.
Nevertheless, the level at which the vessels bifurcate may vary; on
rare occasions, they may have to be mobilized to expose the L5-S1 disc
space.

Note that the left common iliac vein lies below the left
common iliac artery, whereas the right common iliac artery lies below
and medial to the right common iliac vein. Therefore, special care must
be taken

when
mobilizing the left side of the vascular V, because the vessel closest
to the surgery is the thin-walled vein, not the artery (Fig. 6-35; see Fig. 6-34).

A diffuse plexus of nerves exists in the presacral area.
The nerves anterior to the L5-S1 disc are part of the superior
hypogastric plexus which receives sympathetic innervation from T11 to
L3 via the sympathetic chain and a plexus of nerves around the aorta.
Injury to these nerves may cause ejaculatory dysfunction in men
(retrograde ejaculation). More distally the plexus of nerve has
parasympathetic contributions from the pelvic nerves (S2,S3,S4) which
are important for erectile function in men. These nerves are more at
risk with surgeries anterior to the mid and lower sacrum as well as low
rectal and prostate procedures (see Figs. 6-34 and 6-35).¹⁵

The ureter runs down the posterior abdominal wall on the
psoas muscle. At the bifurcation of the common iliac artery over the
sacroiliac joint, it clings to the posterior abdominal wall, held there
by the peritoneum, and should be well lateral to the approach to the
L5-S1 disc space. It may have to be mobilized for exposure of the L4-5
disc space (Fig. 6-36; see Fig. 6-35).

Place the patient on the operating table in the
semilateral position. The patient’s body should be at about a 45° to
90° angle to the horizontal, facing away from the surgeon. Keep the
patient in this position throughout the surgery by placing sandbags
under the hips and shoulders or by using a kidney rest brace to hold
the patient. The angle allows the peritoneal contents to fall away from
the incision. Alternatively, place the patient supine on the operating
table and tilt the table at 45° to the horizontal away from the
surgeon. This position has the advantage of not putting the psoas
muscle on stretch (Fig. 6-37).

The approach can be done with the left or right side up
depending on whether the surgeon prefers to work on the “aortic side”
or the “caval side.”

No internervous plane is available for use. The three
muscles of the abdominal wall (the external oblique, internal oblique,
and transversus abdominis) are divided in line with the skin incision.
Because all three muscles are innervated segmentally, significant
denervation does not occur (Fig. 6-38).

Deepen the incision through subcutaneous fat to expose the aponeurosis of the external oblique

muscle. Divide the aponeurosis of this muscle in the line of its
fibers, which is in line with the skin incision. The muscle fibers of
the external oblique rarely appear below the level of the umbilicus
except in very muscular patients. If they are found there, the muscle
should be split in the line of its fibers (Fig. 6-40).

Next, divide the internal oblique muscle in line with
the skin incision and perpendicular to the line of its muscular fibers.
This division causes partial denervation, but if the muscle is closed
properly, postoperative hernias can be avoided (Fig. 6-41).
Under the internal oblique muscle lies the transversus abdominis
muscle. It, too, should be divided in line with the skin incision to
expose the retroperitoneal space (Figs. 6-42, 6-43, 6-47, and 6-48).

Using blunt finger dissection, develop a plane between the retroperitoneal fat and the fascia that overlies the psoas muscle (Fig. 6-44). Gently mobilize the peritoneal cavity and its contents and retract them medially (Fig. 6-45).
Carry out this dissection from either the left lower quadrant or the
right upper quadrant, depending on the side that needs to be exposed.

Place a Dever-type retractor over the peritoneal
contents and retract them to the right upper quadrant. The ureter,
which is attached loosely to the peritoneum, is carried forward with it.

Identify the psoas fascia, but do not enter the muscle.
Any existing psoas abscess is easily palpable at this point. If one is
found, it should be entered from its lateral side with finger
dissection. Follow the abscess cavity with a finger directly to the
infected disc space or spaces. If there is no psoas abscess, follow the
surface of the psoas muscle medially to reach the anterior lateral
surface of the vertebral bodies.

The aorta and vena cava effectively are tied to the
waist of the vertebral bodies by the lumbar arteries and veins. These
smaller vessels must be located individually on the involved vertebrae
and tied so that the aorta and vena cava can be mobilized and the
anterior part of the vertebral body reached. Make sure that the lumbar
vessels are not cut flush with the aorta; a slipped tie then would
prove hard to deal with (Figs. 6-46 and 6-49).

Place a needle into the involved lumbar vertebra or disc, and take a radiograph to identify the exact location.

Place the patient in the prone position. Move the head
into a few degrees of flexion to open the interspinous spaces. Tongs
and a fixed brace are applied (Mayfield tongs or similar). This allows
for careful control of the head and neck position during the procedure,
minimizes the possibility of ocular pressure, and gives good access by
the anesthetist to the airway (Fig. 6-50).

Alternatively, the patient may be seated upright, with the head held in a special brace. This position

has the advantage of decreasing venous bleeding, but it has been implicated as a cause of air emboli.

Illumination is important; a cold-light headlamp or microscope use adds significant clarity to the operative field.

The internervous plane is in the midline, between the
left and right paracervical muscles (which are supplied segmentally by
the left and right posterior rami of the cervical nerves).

Continue the incision down to the spinous processes.
Minimal bleeding may come from venous plexuses that cross the midline;
these should be cauterized (Figs. 6-52 and 6-53).

Remove the paraspinal muscles subperiosteally from the posterior aspect of the cervical spine either

unilaterally or bilaterally, depending on the exposure needed;
bilateral removal is done for a spine fusion and unilateral removal for
a herniated disc. Use a Cobb elevator or cautery, which can remove the
muscles from the bone without damaging them unduly (Fig. 6-54). Carry the dissection as far laterally as necessary to reveal the lamina and the facet joints (Figs. 6-55 and 6-56). If necessary, cauterize the segmental arterial vessel that runs between the facets.

This dissection is quite safe. If it strays from the
midline and cuts into muscles, however, notable bleeding can occur that
will require immediate cauterization. If the patient has significant
spina bifida, it is possible to enter the spinal canal, injuring neural
tissue.

Identify the ligamentum flavum that runs between the
laminae. With a sharp blade, remove it from the leading edge of the
lamina of the inferior vertebra. Place a flat, spatula-shaped
instrument in the midline in the space between the two ligaments and
cut down on the ligamentum flavum, with the metallic unit separating
the ligamentum from the underlying dura. Perform a laminectomy, either
partial or complete, removing as much of the lamina as necessary to see
the blue-white dura, which lies immediately below it, probably covered
by epidural fat. Identify the posterior portion of the vertebral body,
the disc space, and the possibly herniated disc (Figs. 6-57 and 6-58).
Occasionally, the thin epidural veins surrounding the cord may bleed
significantly. The veins can bleed anywhere; they are hardest to
control between the anterior aspect of the cord and the posterior part
of the vertebral body.

The muscles covering the posterior aspect of the
cervical spine run longitudinally and are supplied segmentally.
Although it is not critical to know the various individual posterior
muscles of the cervical spine, being aware of these muscles and their
layers is helpful. Because the approach itself is in the midline, it
disturbs no vital structures and is relatively safe.

The ligamentum nuchae is a fibroelastic septum that
takes origin from the occiput and inserts into the C7 spinous
processes, sending septa down to each of the cervical spinous processes
and dividing the more lateral paracervical muscles. The septum, which
is almost vestigial in humans, is well developed in quadrupeds, because
it helps the muscles support the head. It is the homologue of the
supraspinous ligament in the rest of the spine. Dissection through it
is safe, as long as it remains in the midline (see Fig. 6-63B).

The paracervical muscles in the cervical spine run in three layers. The most superficial layer
consists of the trapezius muscle, which takes origin from the superior
nuchal line and from all the spinous processes of the cervical spine.
The trapezius covers the entire cervical area; in common with its
counterpart in the lumbar spine, the latissimus dorsi, it is
essentially an upper limb muscle (Fig. 6-59).

The intermediate layer is
filled by the splenius capitis, a relatively large, flat muscle that
takes origin from the midline (spine of C7, the lower half of the
ligamentum nuchae, and the upper three thoracic spinous processes) and
inserts into the occipital bone (Fig. 6-60).

The deep layer is subdivided
into three portions: superficial, middle, and deep. The superficial
portion consists of the semispinalis capitis, a relatively large muscle
that lies immediately beneath the splenius. The semispinalis capitis
takes its origin from the transverse processes of the cervical
vertebrae and inserts into the occipital bone. The middle portion of
the deep layer is filled by the semispinalis cervicis, which originates
from the transverse processes of the upper five or six thoracic
vertebrae

and
inserts into the midline interspinous processes. The deepest portion of
the deep layer consists of the multifidus muscles and the short and
long rotator muscles (Fig. 6-61).

The laminae of the cervical vertebrae are angled from
medial to lateral at 45°. Lateral to the laminae are the joint
capsules, which completely surround the cervical facet joints. The
facet joints are in a frontal plane (Figs. 6-63B and 6-64).

Unless the patient has a large spina bifida, the spinal
canal is safe during this phase of the dissection. A wide, flat
instrument (such as a Cobb dissector) held transverse to the lamina
helps to protect the canal (see Fig. 6-54).

As it does elsewhere in the spine, the ligamentum flavum
connects the lamina on one vertebra to the adjacent vertebra, filling
the space between the two. The ligaments are paired, one on each side,
and may be separated in the midline by a tiny space. They take origin
from the leading edge of the lower lamina and insert proximally into
small ridges on the anterior surface of the higher vertebra, about one
third up the anterior surface.

Each ligamentum flavum extends from the midline laterally to the joint capsule. The spinal cord is directly

beneath the ligamentum flavum. Therefore, the ligament must be removed
carefully, so that the coverings of the cord (the outer dura, the
middle arachnoid, the inner pia) do not tear.

The posterior longitudinal ligament lies on the
posterior surface of the cervical vertebral bodies, within the
vertebral canal, and extends down through the entire spinal canal. The
ligament attaches to each vertebra and disc; it is broadest in the
cervical region. Over the ligament, on the floor of the canal, lie
large vertebral veins, comprising a nonvalvular venous plexus. These
may bleed and require cauterization.

The key vascular structure in the deep dissection is the
vertebral artery. The artery runs upward in the neck through a series
of foramina in the transverse processes of the cervical vertebrae.
Vigorous decortication may breach the posterior walls of these foramina
and damage the artery, which carries a blood supply that is vital to
the hindbrain. The risks are far greater when the transverse processes
are involved in pathology. If the artery is damaged during dissection,
it should be packed to produce at least temporary control of bleeding.
In most situations, this will also produce definitive control;
occasionally, repair of the artery or legatum will be required (see Figs. 6-62 and 6-64).

Place the patient prone, with the head and neck flexed to separate the occiput and the ring of the atlas (C1; see Fig. 6-50).

Deepen the wound in line with the skin incision by
incising the fascia and nuchal ligament in the midline of the neck,
cutting down onto the large spinous process of C2 (Figs. 6-60 and 6-67).
Extend this fascial incision distally onto the spinous process of C3
and then proximally onto the tubercle of C1. Continue proximally,
cutting down onto the external occipital protuberance.

Carefully remove the paracervical muscles from the posterior elements of C1 and C2 (Fig. 6-68).
Use a wide dissecting instrument (such as a Cobb elevator) to avoid
inadvertently breaching the spinal canal. Note that the facet joints
between C1 and C2 are about an inch further anterior than are those
between C2 and C3. Carry the dissection up to the base of the occiput,
if necessary, to expose the superior margin of the ring of C1 (see Fig. 6-68).

If necessary, the ligamentum flavum (posterior
atlantoaxial ligament) can be removed from between C2 and C1, and the
posterior atlantooccipital membrane can be removed from between C1 and
the occiput (Fig. 6-69). This rarely is
necessary. Usually, separating these membranes from bone is all that is
needed to pass a wire underneath the arch of C1 so that the area can
retain bone graft. Once these posterior ligaments have been removed,
the dura of the cervical portion of the spinal cord is uncovered.

C1 and C2 are specialized to permit the extreme motion
of the upper cervical spine. As in other parts of the spine, the
muscles covering C1 and C2 lie in three layers. The outer layer
consists of the trapezius, a muscle of the upper limb. The intermediate
layer is made up of the paraspinal muscles, in this case, the splenius
capitis and the semispinalis capitis.

The anatomy of the area is unique in its deepest layer;
there are four pairs of small muscles that drive the unusual movements
that these joints are capable of. The riskiest part of surgery in the
area occurs in the deepest plane. The vertebral artery, which runs
through the foramen transversarium (still deeper) never should be seen
during dissection, but its position always must be kept in mind.

The ligamentum nuchae, the midline fibrous membrane,
extends from the external occipital protuberance to the spinous process
of the seventh cervical vertebra. A septum extends from its anterior
border; it attaches to the posterior tubercle of the atlas and all the
remaining spinous processes of the cervical spine (see Fig. 6-63B).

The muscles of the superficial and intermediate layers
consist of the trapezius (in the superficial layer) and the splenius
capitis, which covers the semispinalis capitis and the longissimus
capitis (all in the intermediate layer; see Figs. 6-59 and 6-60).

The splenius capitis arises from the thoracic spinous
processes before inserting into the base of the skull. Deep to it lies
the semispinalis cervicis, which inserts onto the axis.

Detaching these muscles uncovers the four unique muscles
of the suboccipital triangle, the rectus capitis posterior major and
minor, and the oblique capitis inferior and superior (see Fig. 6-62).

Because C1 has no spinous process, finding its bony ring posteriorly requires an especially deep dissection (see Fig. 6-63B).

The atlantoaxial and atlanto-occipital membranes, which
form the remaining posterior coverings of the cord, are homologues of
the original ligamentum flavum. The spinal canal at C1-2 is
particularly spacious, allowing extensive motion.

Two important cutaneous nerves intrude into the lateral
aspect of the suboccipital triangle: the greater occipital nerve (the
posterior primary ramus of C2) and the third occipital nerve (the
posterior primary ramus of C3; see Figs. 6-59 and 6-62). The most important structure in the suboccipital triangle is the vertebral artery.
This key blood supply to the hindbrain ascends in the neck through a
series of foramina in the transverse processes. At the level of the
atlas, it pierces the foramen transversarium of the atlas and then
turns medially behind the atlantooccipital joint. To enter the spinal
canal, it pierces the posterior atlanto-occipital membrane at its
lateral angle; therefore, it is extremely vulnerable during dissection
of the atlanto-occipital membrane (see Fig. 6-62).

Place the patient supine on the operating table with a
small sandbag or roll between the shoulder blades to ensure extension
of the neck. Turn the patient’s head away from the planned incision to
provide good access to the side of the neck (Fig. 6-70).
Some cases may require application of halter traction so that it can be
used later if distraction is required. Elevate the table 30° to reduce
venous bleeding and make the neck more accessible. Place the patient’s
arm at his or her side after careful padding.

No internervous plane is available superficially, but
incising or dividing the platysma muscle causes no significant
problems; the muscle is supplied high up in the neck by branches of the
facial (seventh cranial) nerve.

More deeply, the plane lies between the
sternocleidomastoid muscle (which is supplied by the spinal accessory
nerve) and the strap muscles of the neck

(which receive segmental innervation from C1, C2, and C3; see Fig. 6-74, cross section).

Deeper still, the plane lies between the left and right
longus colli muscles, which are supplied separately by segmental
branches from the second to the seventh cervical nerves (see Fig. 6-76, cross section).

The skin and the platysma muscle are very vascular. For
this reason, some surgeons inject the area with a dilute solution of
epinephrine (Adrenalin) before incising the skin.

Incise the fascial sheath over the platysma in line with the skin wound (Fig. 6-72).
Then, split the platysma longitudinally using the tips of the index
fingers, dissecting parallel to the long fibers. The platysma fibers
can also be divided with a knife. Identify the anterior border of the
sternocleidomastoid muscle and incise the fascia immediately anterior
to it (Fig. 6-73). Using the fingers, gently retract the sternocleidomastoid muscle laterally. Retract the sternohyoid

and sternothyroid strap muscles (with the associated trachea and underlying esophagus) medially.

The carotid sheath enclosing the common carotid artery, vein, and vagus nerve now can be exposed, if necessary (Fig. 6-74).

Palpate the artery. Develop a plane between the medial
edge of the carotid sheath and the midline structures (thyroid gland,
trachea, and esophagus), cutting through the pretracheal fascia on the
medial side of the carotid sheath. Retract the sheath and its enclosed
structures laterally with the sternocleidomastoid muscle (Fig. 6-75).

Two arteries connect the carotid sheath with the midline structures. These two vessels, the superior

and inferior thyroid arteries, may limit the extent to which this plane
can be opened up above C3-4. Occasionally, either or both of them may
have to be ligated and divided to open the plane.

Now, develop a plane deep to the cut pretracheal fascia
by blunt dissection, proceeding carefully in a medial direction behind
the esophagus, which is retracted from the midline.

The cervical vertebrae should be visible now, covered by
the longus colli muscle and the prevertebral fascia. The anterior
longitudinal ligament in the midline can be seen as a gleaming white
structure. The sympathetic chain lies on the longus colli, just lateral
to the vertebral bodies (see Fig. 6-75).

Using cautery, split the longus colli muscle
longitudinally over the midline of the vertebral bodies that need to be
exposed (see Fig. 6-75, cross section).
Then, dissect the muscle subperiosteally with the anterior longitudinal
ligament and retract each portion laterally (i.e., to the left and
right of the midline) to expose the anterior surface of the vertebral
body (Fig. 6-76).

Obtain a lateral radiograph after placing a needle marker in the
appropriate vertebral body to identify the level correctly. Make sure
that the retractors are placed underneath each of the longus colli
muscles, widening the exposure while protecting the recurrent laryngeal
nerve, trachea, and esophagus.

Poorly placed retractors endanger the trachea and
esophagus. Unless they are placed underneath the longus colli muscle,
the retractors used should be rounded and hand-held (see Fig. 6-76, cross section).

The key to understanding the anatomy of the anterior
approach to the cervical spine lies in appreciating the three fascial
layers of the neck. The most superficial fascial layer is the investing
layer of deep cervical fascia. The fascia
surrounds the neck like a collar, but splits around the
sternocleidomastoid and trapezius muscles to enclose them. Posteriorly,
it joins with the ligamentum nuchae (nuchal ligament). The superficial
layer is incised along the anterior border of the sternocleidomastoid
muscle. Dividing the layer of fascia allows the sternocleidomastoid to
be retracted laterally and separated from the underlying strap muscles.
The only structures that lie superficial to it are the platysma muscle
(a remnant of the old panniculus carnosus, or muscle of the skin) and
the external jugular vein, which can be divided safely if it intrudes
into the operative field (Figs. 6-77 and 6-78).

The next fascial layer is the pretracheal fascia,
which forms a layer between sliding surfaces. It invests the strap
muscles and runs from the hyoid bone down into the chest (see Fig. 6-78).
Its key relationship is with the carotid sheath, which encloses the
common carotid artery, the internal jugular vein, and the vagus nerve.
The pretracheal fascia is continuous with the carotid sheath at the
sheath’s lateral margin (see Figs. 6-77 and 6-79).
Hence, the pretracheal fascia must be divided on the medial border of
the carotid sheath so that the carotid sheath can be retracted
laterally and the midline structures can be retracted medially. Two
sets of vessels, the superior and inferior thyroid vessels, run from
the carotid sheath through the pretracheal fascia into the midline. On
rare occasions, the thyroid vessels have to be divided to enlarge the

exposure (see Fig. 6-80). The superior laryngeal nerve, however, which runs with the superior thyroid vessels, must be preserved.

The deepest layer of fascia is the prevertebral fascia,
a firm, tough membrane that lies in front of the prevertebral muscles.
On its surface runs the cervical sympathetic trunk, which lies roughly
over the transverse processes of the cervical vertebrae. Beneath the
prevertebral fascia are the left and right longus colli muscles (see Figs. 6-77 and 6-80).

The platysma muscle is split in line with its fibers.
The muscle is difficult to denervate, because most of its nerve supply
comes from the cervical branch of

the
facial nerve and begins in the region of the mandible. In any case, the
muscle is not of great functional importance; sewing it carefully
during closure can improve the cosmetic appearance of the scar.

Dividing the fascia on the anterior border of the sternocleidomastoid muscle reveals the carotid sheath (see Fig. 6-74, cross section).
The sheath contains the common carotid artery, which divides at the
upper border of the thyroid cartilage into internal and external
carotid arteries. It also contains the internal jugular vein and the
vagus nerve (see Fig. 6-79). After the plane
between the carotid sheath and the trachea and esophagus has been
entered, it is easy to develop by blunt dissection. The esophagus,
however, is a fragile structure that is damaged easily by injudicious
retraction.

The longus colli muscles lie on the anterior surface of
the vertebral column, between C1 and T3. The muscles are pointed at
their ends and broad in the middle. They must be removed from the
vertebral bodies to expose the vertebrae. Removal does not denervate
them, because they are innervated segmentally and laterally from their
posterior surfaces. Running on the anterolateral surfaces of the longus
colli muscles is the

cervical sympathetic trunk, with its numerous ganglia. These must be avoided (see Figs. 6-77 and 6-80).

The two recurrent laryngeal nerves are branches of the
vagus nerve. The left recurrent laryngeal nerve descends into the
thorax within the carotid sheath. It curves around the aortic arch and
ascends back in the neck, running between the trachea and esophagus to
supply the larynx. The right recurrent laryngeal nerve descends within
the carotid sheath and curves around the subclavian artery before
ascending into the neck at a higher level than the left recurrent
laryngeal nerve. In addition, the right recurrent laryngeal nerve is,
on rare occasions, aberrant, leaving the carotid sheath at a higher
level and crossing the operative field at the level of the thyroid
gland (see Figs. 6-70 and 6-80).
Thus, left-sided approaches often are preferred. The nerves usually are
safe as long as retractors are placed correctly underneath the longus
colli muscles.

Place the patient prone on the operating table, with
bolsters positioned longitudinally on each side of the rib cage to
allow for chest expansion. Drape widely over the rib cage area so that
the rib cage can be exposed laterally (see Fig. 6-101).

There is no true internervous plane in this approach; it
involves splitting the trapezius muscle and cutting through the
paraspinal muscles. Because the paraspinal muscles are innervated
segmentally, no significant denervation occurs. The trapezius receives
its supply from the spinal accessory nerve higher up.

Incise the subcutaneous fat and fascia in line with the
skin incision, cutting through the trapezius muscle parallel with its
fibers close to the transverse processes. Deep to it are the paraspinal
muscles (Fig. 6-84).

Cut down onto the posterior aspect of the rib to be
resected all the way to bone. The plane often is bloody; a cutting
cautery (diathermy) is useful (Fig. 6-85).

Carefully separate all the muscle attachments from the rib that has been approached, using subperiosteal

dissection with a periosteal elevator (Fig. 6-86).
Dissect laterally along the superior border of the rib and medially
along the inferior border. Continue dissection subperiosteally on to
the anterior surface of the rib. Divide the rib about 6 to 8 cm from
the midline. Then, lift it up and carefully cut any remaining muscle
attachments and the costotransverse ligament. Twist the rib’s medial
end to complete the resection (Figs. 6-87 and 6-88). At this point, the field may flood with a gush of pus from the opened abscess cavity.

Remove all muscle attachments from the transverse
process; divide the process at its junction with the lamina and
pedicle, using a rongeur biting instrument. Remove the transverse
process to gain wider exposure (see Fig. 6-88, cross section).

Carefully enter the retropleural space by digital
palpation and dissection, removing the parietal pleura from the
vertebral body. Note that this plane is safe only if the pleura is
thickened by disease. Careful blunt dissection is essential to avoid
entering the pleural cavity. At this point, the vertebral body and disc
space should have been exposed.

Place the patient on his or her side on the operating
table, stabilizing the patient with a kidney rest or sandbags. Move the
hand and arm on the side to be approached above the patient’s head or
onto an airplane splint (Fig. 6-89). Place a
small pad in the axilla of the dependent side to avoid compression of
the axillary artery and vein. Feel for a radial pulse after
positioning; make sure that there is no venous obstruction in the arm.
The surgeon can be positioned in front of or behind the patient.

Although the thoracic vertebrae can be approached from
either side, approaching from the right side is easier because the
aortic arch and aorta can be avoided.

Divide the latissimus dorsi muscle posteriorly in line with the skin incision (Fig. 6-91). Then, divide the serratus anterior muscle along the same line, down to the ribs (Fig. 6-92). This allows the scapula to be elevated and muscles to be cut proximally to expose the underlying ribs (Fig. 6-93).
It seldom is necessary to cut the more posterior rhomboid muscles.
Because the operation is not performed in an intermuscular plane,
bleeding is a problem; cutting cautery (diathermy) can be used to
control it (Figs. 6-98 and 6-99).

The thoracic cavity can be reached either through an
intercostal space or by resection of one or more ribs. Rib resection
creates a better exposure, and the cut ribs can be used for bone
grafting.

The level at which the chest is entered depends on the
location of the pathology to be treated. Unless the vertebrae involved
are low (between T10 and T12), use the fifth intercostal space (between
the fifth and sixth ribs) for entering the chest, because the scapula
easily overrides the healing site and will
not cause clicking. For pathology at T10 to T12, use the sixth
intercostal space, which provides better exposure of the lower
vertebral bodies. During its range of motion, however, the scapula may
have to jump over the callus formed at the healing site, causing a
click.

To use an intercostal approach, cut down onto the rib
with cutting diathermy. Cut the periosteum on the upper border of the
rib and into the pleura in this line. Entering the pleura from above
the ribs avoids damage to the intercostal nerve and vessels, which lie
along its lower border (Fig. 6-94; see Fig. 6-93).
For greater exposure, strip all muscular attachments from either the
cephalad or the caudad rib (usually the fifth), using a periosteal
elevator or cautery, and resect the posterior three fourths of the rib
as far posterior as necessary (Fig. 6-95).

Insert a rib spreader during either approach to hold the
ribs apart; spread the ribs slowly to allow the muscles to adapt.
Incising the paraspinal muscles seldom is necessary. Ensure complete
hemostasis, especially in the posterior angle, before proceeding.

Ask the anesthesiologist to deflate the lung. Then,
gently retract it anteriorly, using moist lap pads to protect it. Under
it lies the posterior mediastinum. These make identification easier.
Incise the pleura over the lateral side of the esophagus so that the
esophagus can be retracted and the anterior part of the spine reached (Fig. 6-96).
The esophagus is easy to mobilize with finger dissection; retract it
from the anterior surface of the spine with two Penrose drains. The
intercostal vessels cross the operative field; one or more may have to
be tied off (Fig. 6-97). Tying off more
intercostal vessels than is necessary should be avoided, however,
because the blood supply to the spinal cord from these vessels varies.
Damage from ischemia may occur on rare occasions if more than two
sequential intercostal vessels are ligated close to the vertebral
bodies. Approaching the vertebral body from the right side obviates the
need to ligate both the left and right segmental intercostal arteries.
Approaching the vertebrae from the right side is safer and simpler than
is trying to move the aorta itself (Fig. 6-100B).

Place the patient prone on the operating table, with
bolsters along each side so that the anterior chest wall clears the
table and the chest can expand. The bolsters should be long enough to
reach and support the anterior superior iliac spine so that the
anterior abdominal wall clears the table as well; this allows emptying
of the nonvalvular vertebral venous plexus into the vena cava, reducing
operative bleeding (Fig. 6-101).

The paraspinal muscles are innervated segmentally by the
posterior primary rami of the individual nerve roots in the thoracic
and lumbar spines. Because the incision is in the midline, it is truly
internervous; the nerves do not cross the midline.

Palpate the individual spinous processes. Determine
whether they have deviated from the midline as they rotate in
scoliosis. Continue dissecting down to the middle of the spinous
processes and move the muscle origins to either side of the surface. In
children, split the spinous process apophyses longitudinally and
dissect them to each side of the processes with a Cobb elevator (Fig. 6-103).

Remove the paraspinal muscles from the spinous processes and partially from the laminae by subperiosteal dissection (Fig. 6-104).
In the thoracic area, work in a distal to proximal direction, in the
direction of the muscle fibers along the spinous process. After the
paraspinal muscles have been stripped from the spinous processes and
laminae, keep the dissection open with self-retaining retractors (Fig. 6-105).

Now, still using the Cobb instruments, remove the short
rotators from the base of the spinous processes to the leading edges of
the laminae. Then, strip the muscles from the rest of the laminae
laterally, onto the transverse processes (Figs. 6-106 and 6-107).

The posterior primary rami
emerge posteriorly from between the transverse processes, close to the
facet joints. Because of the significant overlap of innervation in the
paraspinal muscles, loss of an individual posterior primary ramus is
not harmful (see Figs. 6-106B and 6-111).

Segmental vessels coming
directly off the aorta appear between the transverse processes and
supply the paraspinal muscles. They bleed when muscles are stripped
from the transverse processes and must be

cauterized. The posterior primary rami are close to these vessels (see Figs. 6-106B and 6-111).

To determine a precise anatomic location, identify the
12th (last) rib and dissect one level distal to it to locate the
transverse process of L1. Note that the last rib is mobile, a floating
rib without sternal attachment, whereas the transverse process of L1 is
quite rigid and firm, and does not yield to pressure. The rib also is
longer and more tubular than the transverse process (see Fig. 6-100).
After the last rib has been found, identify the nearby facet joints.
The descending facet joint of T12 is a lumbar facet joint, set in the
sagittal plane, whereas the ascending facet joint at the

upper end of T12 is a thoracic facet joint, set in a frontal plane (see Fig. 6-110).
Identifying the direction of facets, the last rib, and the first lumbar
transverse process provides a precise anatomic location. The only
alternative is to place markers in the spinous processes in the lumbar
area and to obtain a radiograph, or to carry the dissection distally
and identify the sacrum.

The musculature in the lumbar area may be stripped at
each vertebral level, either in a proximal to distal direction or in a
distal to proximal direction. A half-inch osteotome may be used in
conjunction with the Cobb elevator to strip the facet joint capsules
from the ascending and descending facets, and to continue the
dissection laterally onto the transverse processes (see Fig. 6-106B).

The posterior muscles of the thoracic and lumbar spines are arranged in three layers:

These distinct layers are not actually seen during
surgical exposure of the spine, but the layering concept clarifies how
the anatomy relates to the dissection.

The superficial layer of
muscles can be subdivided into two layers: the most superficial layer
consists of the trapezius and latissimus dorsi; the deeper layer is
composed of the rhomboid major and minor.

The intermediate layer
consists of the serratus posterior superior and the serratus posterior
inferior, which are small, laterally placed muscles that attach to the
spine.

The deep layer includes the
sacrospinalis muscles (erector spinalis) and a deep, obliquely running
layer consisting of the semispinalis, multifidus, and rotator muscles.

The muscles of the superficial layer are supplied by the
peripheral nerves: the trapezius by the spinal accessory nerve, the
rhomboids by the nerve to them from C5, and the latissimus dorsi by the
thoracodorsal nerve. They are not affected by a midline dissection.

The muscles of the intermediate layer are supplied by the anterior primary rami; they, too, are unaffected by the dissection.

The muscles of the deep layer are supplied segmentally
at each level of the spine by the posterior rami of the thoracic and
lumbar nerves. Their nerve supplies usually are safe, but they may be
denervated partially by excessive lateral dissection.

The C7 and T1 spinous processes are the largest
processes in the region, with T1 being slightly larger. They point
directly posteriorly, with minimal caudal angulation, and are easily
palpable. The large L5 spinous process, which also has minimal caudal
angulation, can be palpated, but it cannot be differentiated from the
other equally large lumbar spinous processes. The gluteal cleft, which
runs between the protuberances of the gluteal (cluneal) muscles, is
easy to see.

The skin on the posterior aspect of the spine is thicker
than that on the anterior chest wall and abdomen. It usually heals with
a fine line scar because there is so little tension across the sutured
incision. The skin in the lumbar region (which is dissected
subcutaneously to leave the iliac crest accessible for a bone graft)
and the skin in the thoracic region (which is dissected subcutaneously
to reach the ribs) heal well, despite the subcutaneous dissection.
Dimpling of the skin over the iliac crest or ribs does not occur as
long as the thick, subcutaneous, fatty tissue layer is taken with the
skin to prevent it from adhering to the cut bony surfaces.

The tips of the spinous processes in the thoracic region
are much narrower than are those in the lumbar area, and more muscles
attach directly to their tips. As a result, dissection must approach
the tips of the spinous processes exactly in the midline, without
straying to either side. More bleeding occurs in the thoracic region,
mainly because of the direct attachment of muscle fibers from the
trapezius and rhomboid muscles; in the lumbar area, only the relatively
avascular lumbodorsal fascia attaches to the tips of the lumbar and
lower thoracic processes (Fig. 6-108). If the
patient has scoliosis with extensive vertebral body rotation, the
paraspinal muscles on the convex side of the curve may bunch up and
roll over the tips of the spinous processes, causing further bleeding
if the muscles are cut inadvertently during dissection.

The deep layer of the back consists of a superficial
portion and a deep portion. The superficial portion is made up of the
sacrospinalis muscle (the erector spinae), which runs longitudinally.
In the lumbar area, the muscle is a single mass; in the thoracic
region, it divides into three units, namely, from medial to lateral,
the spinalis, the longissimus, and the iliocostalis (see Figs. 6-108 and 6-111).

The deep portion of the deep layer itself has three
layers: superficial, intermediate, and deep groups. The superficial
group consists of the semispinalis muscles, which span about five
segments from origin to insertion. The intermediate group, the
multifidus muscles, spans about three segments. The deep group, the
rotator muscles, spans adjacent segments (Figs. 6-109 and 6-110; see Fig. 6-108).
The rotator muscles pass in a lateral to medial direction, with the
distal end of the muscle being more lateral. The resulting angle
between the muscle and its insertion makes stripping the muscles in a
caudad to cephalad direction in the thoracic region easier (see Figs. 6-105 and 6-108, 6-109 and 6-110).
In addition, because the spinous processes are angled more caudally in
the thoracic area than in the lumbar area (where they stand erect,
almost directly over the vertebral bodies), it is easier to dissect the
paraspinal muscles free from the thoracic spinous processes in a distal
to proximal direction. Finally, the short rotators take origin from the
caudal end of the spinous processes and are detached easily and
dissected out laterally onto the transverse processes (see Figs. 6-105 and 6-110).

The transverse processes themselves should be stripped
of musculature in a distal to proximal direction. The transverse
processes become larger from T12 to T1.

Intermediate surgical dissection avoids the middle layer
of back muscles, the muscles of respiration; these are placed more
laterally.

The posterior primary rami of the paired thoracic and
lumbar nerves may be injured during dissection of the muscles,
particularly laterally between the transverse processes where the rami
are located. Although the loss of one or two posterior primary rami may
denervate the paraspinal muscles partially, the significant overlap of
the segmental nerve supply to these muscles prevents total denervation.
Excessive lateral retraction and cauterization at each level, however,
can cause muscle denervation.

Segmental vessels come directly off the aorta in the
lumbar and thoracic areas; they are located between the transverse
processes, close to the posterior primary rami. The vessels constitute
the main blood supply to the paraspinal muscles. Cauterizing

them
does not appear to cause significant loss of blood supply to the
muscles. If they are cut, they must be cauterized or tied off; they
branch directly from the aorta and may cause postoperative bleeding
under pressure (Fig. 6-111; see Figs. 6-105 and 6-106B).

The lumbar facet joints and their capsules are much
larger than their thoracic counterparts and protrude further
posteriorly. Their size is mainly the result of their large
articulating processes and large mamillary

processes
that sit on the posterior aspect of the ascending processes, extending
the bone even further posteriorly. The lumbar facet joints lie in the
sagittal plane (see Fig. 6-111B).
The joint capsules themselves are shiny, usually quite white, and are
continuous with the ligamentum flavum, which is yellow-white. In the
thoracic region, the joints are smaller, do not protrude as far
posteriorly, are flatter, and are placed in the frontal plane (see Fig. 6-111A). The facet joints are vulnerable during removal of the joint capsules.

The ligamentum flavum, which originates from the leading
edge of the inferior vertebra and extends upward to a ridge under the
lamina of the next vertebra, covers the blue-white dura and its layer
of epidural fat. The dura must be protected; any epidural tear must be
closed off (see Figs. 6-11 and 6-12).

The cup-shaped ascending articulating process is closest
to the lumbar nerve root. Arthritis of the medial end of the ascending
facet can cause compression of the nerve in the foramen. The nerve root
is safe during the foraminotomy if the anatomic arrangement of the
facet joints to the nerve root is appreciated. The nerve root should be
protected while the medial portion of the ascending process, the
portion that is close to the nerve root, is being removed (see Fig. 6-111B).

Place the patient prone on the operating table. Position
bolsters longitudinally on either side of the patient from the anterior
superior iliac spine to the shoulders to allow room for chest expansion
(see Fig. 6-101).

The internervous plane lies between the trapezius and
latissimus dorsi muscles. The trapezius is innervated by the spinal
accessory nerve and the latissimus dorsi is innervated by the long
thoracic (thoracodorsal) nerve. The deeper muscle, the iliocostalis
portion of the sacrospinalis, is innervated segmentally and, therefore,
is not denervated when it is split longitudinally.

With retractors, lift the skin and its thick
subcutaneous tissue. Free them from the underlying fascia and retract
them laterally. Center the dissection over the most prominent, or
apical, rib. Extend it laterally to at least 12 cm from the midline,
and then proximally and distally to expose all the deformed ribs (Fig. 6-112).

The fibers of the trapezius muscle run obliquely
downward toward the midline as far as the spinous process of T12.
Identify this muscle by its rolled, lateral free border. Dissect along
the lateral border and retract the muscle medially. The medial portion
of the fibers of the latissimus dorsi muscle and its aponeurosis run
almost perpendicular to and under the trapezius muscle; it takes origin
from the lower six thoracic spinous processes, as well as from the
lumbodorsal fascia. Dissect the muscle free with cautery and retract it
laterally (see Fig. 6-112).

Below the retracted trapezius and latissimus dorsi
muscles lies the iliocostalis, a longitudinal muscle with flattened
tendons in its musculature that insert into the lower borders of the
ribs. Split the iliocostalis muscle longitudinally over each of the
deformed portions of the ribs that are being removed, then dissect and
retract it medially and laterally in line with the ribs (Fig. 6-113).

Incise the periosteum along the posterior aspect of the rib in the rib’s own plane. Use an Alexander

dissector to push the split periosteum to the upper and lower borders
of the rib. With the special end of the dissector, strip the
intercostal muscles off the upper end of the rib in a medial to lateral
direction in the angle formed by the intersection of the external
intercostal muscles and the rib. Then, strip the intercostal muscles
from the lower end of the rib in a lateral to medial direction,
remaining in the angle formed by the origin of the external intercostal
muscle and the rib to discourage bleeding. By keeping the dissection in
a subperiosteal location, the neurovascular bundle, which will have
been freed from the lower border of the rib with the intercostal
muscles, will be avoided (Fig. 6-114).

Before continuing, have the anesthesiologist stop the
patient’s breathing so that the visceral pleura can fall away from the
rib, minimizing the danger to the pleura during anterior dissection.
When the ribs have been uncovered completely, begin to resect them.

The neurovascular bundle
lies along the lower edge of the rib in the neurovascular groove.
Unless the dissection is kept in a subperiosteal location, it may be
cut inadvertently during the resection and the intercostal vessels will
have to be cauterized, causing possible segmental chest wall numbness
(see Fig. 6-114, inset).

Violating the pleura may result in a pneumothorax.
1f that happens, plan to insert a chest tube immediately after the
wound is closed, while the patient is still in the operating room.

Connecting the midline wound with that of the rib resection may cause a hemothorax,
with blood flowing from the area of the spinal fusion into the lung. If
the two areas of dissection are connected, be prepared to insert a
chest tube to drain the blood.

The skin may adhere to the
cut ends of the ribs, causing unsightly dimpling. To prevent this, take
a thick subcutaneous layer with the skin and, during

closure, suture the fascia of the trapezius muscle to that of the latissimus dorsi muscle.

When removing ribs, resect each one from the point just
lateral to its maximum deformity to the most medial end, without
removing its head and neck. The lateral portion of the resected rib
will drop forward, reducing the rib hump, but the medial portion, held
rigidly in place by the costotransverse and costovertebral ligaments,
will not move. That is why the rib should be resected as medially as
possible. Otherwise, the medial end of the rib will continue to stick
out posteriorly, causing continued deformity.

The removal of more than four ribs may cause a
sympathetic effusion of a lung field. If this occurs, insert a chest
tube to drain the fluid.

Treat the cut ends of the ribs with bone wax to prevent
continued oozing of blood. The wax does not prevent the ribs from
regenerating.

The resected portions of the ribs can be cut into small,
matchstick-sized pieces and used as graft material in a midline spine
fusion.

If the vertebral body has rotated up under the rib,
resecting the ribs will not produce a significant reduction in the rib
hump deformity.