Step 1: Medical Evaluation
Patients with severe spinal deformity often have accompanying underlying
medical comorbidities, which frequently require attention before proceeding
with surgery. Most commonly, patients with severe spinal deformity have
diminished pulmonary function, often requiring evaluation by a pulmonary
specialist. Patients may also be nutritionally depleted and may require
nutritional supplementation; in severe cases, patients may require insertion
of a gastrostomy tube. Other medical issues also may exist and should be
addressed before surgery according to the individual needs of the patient.
Step 2: History, Physical Examination, and Radiographic
Evaluation
Before surgery, a thorough history should be acquired and a physical
examination should be performed, with close attention paid to the neurologic
status of the patient, the overall coronal and sagittal balance, and the
magnitude, extent, location, and flexibility of the spinal deformity. For the
radiographic evaluation, standard anteroposterior and lateral plain
radiographs of the spine should be made with the patient in a standing or a
sitting position, depending on the neurologic status of the patient. In
addition, traction radiographs made in the side-bending, prone,
hyperextension, and, in particular, the supine position can be essential,
especially for patients with severe spinal deformity. In our experience,
traction films are particularly helpful in predicting the amount of correction
that can be obtained with temporary internal distraction; typically, temporary
internal distraction leads to greater correction of the deformity than can be
seen on the traction films. If a large curve corrects by more than 50% on
traction films, external traction or temporary internal traction is unlikely
to be necessary. Because the patients undergoing this procedure have large
deformities and will be undergoing distraction of the spine, magnetic
resonance imaging of the cervical, thoracic, and lumbar spine should also be
obtained before surgery. Lastly, for patients with severe deformity, computed
tomography may be helpful because it allows careful and precise evaluation of
the osseous spinal anatomy.
Step 3: Preoperative Surgical Planning
Typically, temporary internal distraction requires one procedure in advance
of the main corrective surgical procedure. During the first surgery,
soft-tissue releases and osteotomies are performed, and one or two temporary
rods are placed. During the second procedure, which typically takes place
approximately one week later, the temporary rods are removed, the final spinal
implants are placed, and arthrodesis is performed.
Before surgery, the type and location of the osseous anchor points for the
temporary distraction rod or rods should be planned on the basis of the
preoperative radiographic studies. A basic principle in choosing the anchor
points for the temporary rod is to expect that the anchor points will likely
loosen during the distraction, potentially compromising the purchase of the
final anchor points. Therefore, the surgeon should not plan to use the
temporary anchor points as permanent anchors at the cephalad or caudad end of
the final construct. For example, pedicle screws likely will loosen cranially
in the cephalad portion of the thoracic spine during the distraction,
compromising these fixation points and making them unreliable for use as end
anchor points at the cephalad aspect of the final implant.
Typically, the cephalad portion of the temporary distraction rod is
attached to the ribs or the spine. When attaching the rod to the ribs,
standard spinal laminar hooks may be used. Attaching the rod to two ribs
(rather than one) is preferred because it will disperse the substantial loads
that are applied to the spine. If only one rib is used, the hook may tear
through it. An advantage of applying the temporary rod to the ribs rather than
the spine is that the spine is then left free, allowing for continued
distraction when the permanent rod is fixed to the spine during the final
correction stage. If the spine is chosen as a cephalad anchor point, hooks
generally are preferable to pedicle screws for two reasons. First, the
cephalad aspect of the cortical wall of the pedicle is weaker than the caudal
aspect. Therefore, when a distraction force is applied against a
screw in the cephalad portion of the thoracic spine (i.e., the screws are
pushed "upward"), it is easier to break through the pedicle and
weaken the screw purchase—and potentially ruin the pedicles as permanent
fixation points—than when a compression force is applied
against a screw in the cephalad portion of the thoracic spine (i.e., the
screws are pushed "downward"). Second, as the curves for which
this procedure is performed typically exceed 100°, it is easier to align
up-going infralaminar or transverse process hooks, which have a little bit
more "sloppiness" than pedicle screws, which may not align in a
direction toward the bottom of the construct. For the same reason, when
planning the placement of the cephalad and caudad anchor points, it is often
advisable to place fixation points one to two levels above and below the most
inclined vertebrae to allow the anchor points to line up with a straight
distraction rod.
The caudad anchor points usually are located in the lumbar spine or pelvis.
Because the pedicles typically are stronger in the lumbar spine than in the
thoracic spine, and because a downward force is being applied, the use of two
pedicle screws as a caudad anchor is reasonable. In patients with pelvic
obliquity, or when the final fusion will be to the pelvis, the pelvis or iliac
crest may be chosen as an anchor point. This anchor may be in the form of an
s-shaped hook or a temporary iliac screw. With an iliac screw, a small amount
of migration is common during use of the distraction rod because of the
substantial forces applied to the rods. For this reason, a temporary iliac
screw should be placed superior and lateral to where the permanent iliac screw
will be placed or placed in a standard fashion with the caveat that it may
need to be replaced at the time of the definitive procedure with a larger and
longer screw if loosening has occurred. Alternatively, an s-shaped hook may be
placed over the top of the iliac crest or the sacral ala. Whichever type of
anchor is chosen, there is a mechanical advantage in correcting pelvic
obliquity if the anchor is placed lateral to the spine. An adequate amount of
surgical time should be scheduled to allow for complete release and slow,
gradual intraoperative correction.
Step 4: Patient Positioning
Surgery is performed with the patient in the prone position on a Jackson
spinal table (Orthopedic Systems, Union City, California) or on a flat version
of this table (or radiolucent alternatives). Longitudinal chest rolls may be
used in children of all sizes, but they are particularly helpful in small
children. Although other tables may be used, the advantage of the Jackson
table is that the table is quite versatile and allows for intraoperative
alterations in patient positioning throughout the operation. The goal of
positioning the patient before the application of instrumentation is to
correct the body alignment as much as possible to lessen the amount of force
that is needed to achieve the desired amount of intraoperative correction.
Temporary intraoperative traction with Gardner-Wells tongs can be a helpful
adjunct, and the tongs can be released as the instrumentation is added and the
spine is distracted.
Step 5: Prophylactic Antibiotics
Antibiotics should be administered preoperatively. The choice of
antibiotics is dependent on the surgeon, but we typically use a combination of
first-generation cephalosporin (typically cefazolin) or vancomycin for
gram-positive coverage and a third-generation cephalosporin (ceftazidime or
cefepime) or gentamicin for gram-negative coverage. We believe the addition of
gram-negative coverage is important because patients undergoing temporary
internal distraction typically have comorbidities that put them at a higher
risk of postoperative wound infection from a broad spectrum of organisms.
Step 6: Neuromonitoring
Reliable neurologic monitoring is absolutely essential during distraction
of the spine; indeed, the operation should not be performed if neuromonitoring
is not available. In our practice, patients are monitored continuously with
neurogenic mixed evoked or transcranial motor evoked potentials and
somatosensory evoked potentials. Triggered electromyography may be used to
test pedicle screws.
Step 7: Exposure
The skin incision is made in a standard fashion. Subperiosteal dissection
is carried out down to the osseous anchor points first, before dissection of
the entire spine. The goal is to place the temporary rod in the spine and
begin distraction as early as possible in the procedure. Doing so takes
advantage of the viscoelastic nature of the spine to allow continuous
correction of the deformity during the rest of the surgical procedure.
Step 8: Placement of Cephalad Anchor Points
Through a midline incision, subperiosteal dissection is carried out along
the laminae. Two infralaminar or pedicle hooks may be placed in standard
fashion. The hooks should be placed in laminae that are not intended to be the
final cephalad fixation points for the eventual fusion because some plowing
through of the bone may be expected as a distraction force is applied. As
described above, the ribs also may be used as temporary cephalad anchor
points. To approach the ribs, subperiosteal dissection is carried out, first
along the lamina, then laterally over the transverse processes, until the
medial aspects of the ribs are palpated. In an effort to obviate entering the
chest, the ribs then should be dissected subperiosteally along their anterior
surfaces; circumferential subperiosteal dissection of the ribs usually is not
necessary. Standard laminar hooks may be placed on the rib in an upgoing
fashion. Before closure, the exposure area of the ribs should be filled with
warm saline solution, and a Valsalva maneuver should be performed to assess
whether the chest cavity has been entered. If it has been, a small drain with
a one-way valve to act as a chest tube for drainage may be placed. Formal
chest-tube drainage usually is not necessary.
Step 9: Placement of Caudad Anchor Points
Most commonly, standard lumbar pedicle screws are used as the caudad anchor
points. In general, two screws are used at adjacent vertebrae, but the number
of screws may be adjusted depending on the quality of the bone. As an
alternative, supralaminar hooks may be used. Although it is not as important
to do so in the lumbar spine as in the thoracic spine, vertebrae cephalad to
the end vertebrae of the final construct should be chosen because some
loosening of the temporary anchor points should be expected as a result of
distraction.
If the pelvis is used for the caudad anchor points, the iliac crest should
be exposed. If an iliac screw is to be used, the posterior-superior iliac
crest should be identified before screw insertion. Typically, a fairly stout
and long iliac screw can be placed heading close to (but not entering) the
sciatic notch. If an iliac screw is to be used in the final construct, the
temporary iliac screw may be placed parallel and at least 2 cm lateral to
where the permanent iliac screw will be placed to avoid compromising the
purchase of the permanent screw; alternatively, the temporary iliac screw may
be placed through the standard (final) starting point and trajectory and be
replaced with a longer or thicker screw if necessary at the time of the final
procedure. Because the iliac crest becomes thinner toward the lateral border
in small patients, a second screw may not engage an adequate amount of bone,
in which case an s-shaped hook should be used. To place an s-shaped hook, the
iliac crest should be dissected to the highest point. In patients in whom the
iliac apophysis is still cartilaginous, the cartilage should be left intact
because it serves as a bumper to prevent migration of the s-shaped hook into
the iliac crest. The muscle attachments should be dissected with a cautery
from the top of the iliac crest. Depending on the size of the bone and the
s-shaped hook, the inner and outer tables may need to be dissected in a
subperiosteal manner, or alternatively, the muscle attachments may be left
intact. The inner table of the iliac crest should be palpated anteriorly,
creating a tunnel that allows placement of the s-shaped hook. The single-rod
portion of the s-shaped hook then may be slipped over the top of the iliac
crest anteriorly along the tunnel created by the finger.
Although orthopaedic surgeons may have limited familiarity with this area
of the body, there are no vital structures in this region that are prone to
injury, as long as dissection remains along the iliac crest or the iliac
muscle and does not venture anteriorly into the retroperitoneal space. The
advantage of using an s-shaped hook rather than an iliac screw is that it is
easier to place an s-shaped hook more laterally than an iliac screw; the more
lateral position creates a substantial moment arm that can help to correct
pelvic obliquity. In addition, an s-shaped hook is technically easy to connect
to the distraction rod with a side-to-side connector.
Step 10: Placement of Temporary Distraction Rods
The simplest construct is to attach one rod to the cephalad anchor points
and a second rod to the caudad anchor points, with the two rods connected by a
side-to-side connector and with a great deal of overlap of the rods.
Distraction then is applied across these rods in a serial fashion by loosening
and tightening the side-to-side connector. For large curves, it may be a
challenge to align the anchor points and the attached rods to permit the use
of a connector, but usually a combination of distraction and rod manipulation
can make the rods parallel to each other. On occasion, in patients with
extreme deformity, it may be necessary to apply a short rod to the cephalad
anchor points and another short rod to the caudad anchor points and then
connect these two rods to a third rod with multiaxial crosslink connectors. As
distraction is applied and the deformity is partially corrected, this
configuration usually can be replaced by lower profile rods as described above
(Figs. 1-A through 1-D). It
must be emphasized that as distraction is applied, careful attention should be
paid to the function of the spinal cord. If there is a change in the
neurologic potentials being monitored, distraction should be aborted and the
amount of correction obtained should be decreased. A Stagnara wake-up
test10 should be
performed if a depression in spinal cord signal is noticed by the
electrophysiologist.
Step 11: Releases and Osteotomies
Once the temporary rod or rods are placed and distraction has been applied,
the remainder of the spine between the anchors should be exposed in a
subperiosteal manner. Attention then is turned to the performance of releases
that allow additional correction of the deformity. In most patients, a wide
posterior release at each level of the rigid portion of the curve will need to
be performed, particularly to allow better correction of these severe curves.
This procedure involves release of the entire ligamentum flavum and the
complete facet, including the entire capsule. Additional anchor points
(typically pedicle screws) may be placed at this time, although doing so may
be technically difficult at times, particularly at the concavity at the apex
of the deformity, because the temporary rods can physically impede the
placement of pedicle screws into the rotated vertebral bodies. Fortunately,
this limitation lessens over time with additional distraction maneuvers, and
it may be possible to place pedicle screws at a later time (after osteotomies
and additional distraction, or at the time of the second surgery) if they
could not be placed initially. Implant placement should be done with an eye to
minimizing prominence in anticipation of the final closure. An effective
alternative is to use sublaminar wires at the apex of the deformity, which
helps to translate the spine medially in an iterative fashion with subsequent
tightening and retightening of the wires during placement of the final
rod.
The key and essential part of temporary internal distraction is to apply
multiple episodes of small amounts of distraction throughout the operation to
take advantage of the viscoelastic properties of the spine and allow maximum
correction of the deformity with minimal stress on the tissues and implants.
The passage of time, soft-tissue dissection, facetectomies, and osteotomies
allow additional correction of the spinal deformity. At the conclusion of the
surgery, the aim should be a deformity correction that is greater than that
shown on the supine traction films and that provides =50% correction in the
Cobb angle. If a second rod can be placed without prominence, it will minimize
loosening of the anchors and facilitate mobilization of the patient. This
placement typically is done with one to two anchors at the cephalad and caudad
ends of the curve. No bone graft is used at the initial procedure because
fusion is not the goal. However, any bone obtained in the process of release
or resection may be "stored" laterally in the lordotic portion of
the wound.
Step 12: Closure
The wound should be irrigated thoroughly before closure. Although we are
not aware of the occurrence of any infections related to this procedure in our
practice, we typically use jet lavage and antibiotic-detergent solution to
decrease the risk of an infection. At times, closure can be challenging
because substantial lengthening of the soft tissues takes place with
distraction. Furthermore, the temporary rod or rods are usually lateral to the
transverse processes, making the closure difficult. It often is necessary to
raise thick local flaps, including the paraspinal muscles (i.e., the
trapezius, latissimus dorsi, and rhomboids) to make closure possible. The
potential dead space created during the closure should be drained with closed
suction drains to decrease the risk of infection.
Step 13: Postoperative Management
The primary postoperative concern for patients who undergo this procedure
is nutritional status. These patients require staged surgery, so postoperative
total parenteral nutrition is recommended until adequate oral intake is
achieved. Mobilization, including sitting, standing, and walking, is
encouraged to avoid pulmonary and other complications. No brace or cast is
required. The posterior skin should be inspected regularly to ensure that
there is no breakdown over osseous or implant prominences, which could
jeopardize the final procedure.
Step 14: Final Definitive Surgery
The final surgery is performed as soon as the patient is medically ready.
The sooner that this surgery occurs, the less dissection and bleeding will be
involved. A one-week period appears to be the optimal amount of time between
procedures because it provides enough time for the patient to recover from the
insult of surgery and for the spine and soft tissues to "relax"
after the temporary distraction, thus allowing the surgeon to reexpose the
spine easily during the definitive surgery. Although staging between
procedures may be longer if necessary, a longer period of distraction does not
improve the ultimate correction and may result in a more difficult and bloody
exposure because the released paraspinal tissues may have readhered to the
spine. During this procedure, the spine is reexposed and the temporary
construct is left in place as long as is feasible while additional anchor
points are created. A substantial increase in the ability to correct the spine
should be possible, and it may even be possible to effect additional
distraction at this time. The temporary instrumentation then is removed, and
the final implants are inserted. Repeat pulsed irrigation and drainage then is
performed. Figures 2-A, 2-B, and
2-C and Figures 3-A, 3-B, and
3-C show the decreased curve magnitude in two patients after the
temporary internal distraction procedure and after the final operation.
CRITICAL CONCEPTSGradual correction of the spine may prevent the need for anterior
release.Anchors should be planned to control the curve yet avoid jeopardizing the
final fixation points.Because the curves are large, correction should be done very gradually with
optimal spinal cord monitoring.INDICATIONS:Severe, rigid scoliotic deformity.CONTRAINDICATIONS:Spinal cord abnormality that would preclude deformity correction and/or
distraction (e.g., tethered cord, syrinx).Inability of the patient to tolerate staged procedures secondary to medical
comorbidities or poor nutritional status.Inability to achieve adequate fixation points to allow distraction.Inability to monitor the function of the spinal cord continuously with
neuromonitoring.A substantial rigid kyphoscoliosis may be a relative contraindication.PITFALLS:The use of the most cephalad and caudad fusion levels as fixation points
for the temporary distraction rod may result in inadequate purchase of the
final fixation points because some loosening of the implants is expected when
a distraction force is applied.Postoperative infection at the surgical site is a potential risk with this
process; therefore, careful attention needs to be paid to choice and
administration of prophylactic antibiotics, soft-tissue handling, wound
closure, and the nutritional status of the patient.Because there is a risk of flattening the normal sagittal contours with
distraction, careful attention must be paid to the sagittal profile during the
procedure.AUTHOR UPDATE:With additional experience, we have found that usually only one temporary
internal distraction procedure is necessary to achieve the desired correction.
Therefore, we recommend critically evaluating the need for a second temporary
distraction procedure and performing additional distraction procedures only in
patients with the most severe scoliosis. We also have learned that the optimal
amount of time between the initial and final procedures is approximately one
week. After one week, if the patient is medically ready, the spine is easily
reexposed with little additional dissection. Although the time between
procedures can be longer (for instance, six to eight weeks) if desired or
necessary for medical or social reasons, a period of internal distraction of
longer than one week does not lead to improved curve correction. In fact,
longer periods between the procedures may permit the released paraspinal
tissues to readhere and thus result in increased blood loss during the second
operation. As a final point, we have learned that one important advantage of
temporary internal distraction is that anterior releases are generally
unnecessary and that sufficient correction can usually be obtained through
posterior surgery alone, thus avoiding the patient morbidity that accompanies
anterior thoracic, thoracoabdominal, or abdominal approaches.
CRITICAL CONCEPTS
Gradual correction of the spine may prevent the need for anterior
release.Anchors should be planned to control the curve yet avoid jeopardizing the
final fixation points.Because the curves are large, correction should be done very gradually with
optimal spinal cord monitoring.
Gradual correction of the spine may prevent the need for anterior
release.
Anchors should be planned to control the curve yet avoid jeopardizing the
final fixation points.
Because the curves are large, correction should be done very gradually with
optimal spinal cord monitoring.
INDICATIONS:
Severe, rigid scoliotic deformity.
Severe, rigid scoliotic deformity.
CONTRAINDICATIONS:
Spinal cord abnormality that would preclude deformity correction and/or
distraction (e.g., tethered cord, syrinx).Inability of the patient to tolerate staged procedures secondary to medical
comorbidities or poor nutritional status.Inability to achieve adequate fixation points to allow distraction.Inability to monitor the function of the spinal cord continuously with
neuromonitoring.A substantial rigid kyphoscoliosis may be a relative contraindication.
Spinal cord abnormality that would preclude deformity correction and/or
distraction (e.g., tethered cord, syrinx).
Inability of the patient to tolerate staged procedures secondary to medical
comorbidities or poor nutritional status.
Inability to achieve adequate fixation points to allow distraction.
Inability to monitor the function of the spinal cord continuously with
neuromonitoring.
A substantial rigid kyphoscoliosis may be a relative contraindication.
PITFALLS:
The use of the most cephalad and caudad fusion levels as fixation points
for the temporary distraction rod may result in inadequate purchase of the
final fixation points because some loosening of the implants is expected when
a distraction force is applied.
Postoperative infection at the surgical site is a potential risk with this
process; therefore, careful attention needs to be paid to choice and
administration of prophylactic antibiotics, soft-tissue handling, wound
closure, and the nutritional status of the patient.
Because there is a risk of flattening the normal sagittal contours with
distraction, careful attention must be paid to the sagittal profile during the
procedure.
AUTHOR UPDATE:
With additional experience, we have found that usually only one temporary
internal distraction procedure is necessary to achieve the desired correction.
Therefore, we recommend critically evaluating the need for a second temporary
distraction procedure and performing additional distraction procedures only in
patients with the most severe scoliosis. We also have learned that the optimal
amount of time between the initial and final procedures is approximately one
week. After one week, if the patient is medically ready, the spine is easily
reexposed with little additional dissection. Although the time between
procedures can be longer (for instance, six to eight weeks) if desired or
necessary for medical or social reasons, a period of internal distraction of
longer than one week does not lead to improved curve correction. In fact,
longer periods between the procedures may permit the released paraspinal
tissues to readhere and thus result in increased blood loss during the second
operation. As a final point, we have learned that one important advantage of
temporary internal distraction is that anterior releases are generally
unnecessary and that sufficient correction can usually be obtained through
posterior surgery alone, thus avoiding the patient morbidity that accompanies
anterior thoracic, thoracoabdominal, or abdominal approaches.