Congenital kyphosis and kyphoscoliosis are uncommon deformities that
result from abnormal embryonic development of the spine; specifically, these
deformities are the result of segmentation anomalies that affect the
longitudinal growth of the spine in the sagittal and coronal planes. The
natural history of congenital kyphosis has been well
documented1-3
and the deformity has been classified into three types according to the system
originally proposed by McMaster and
Singh1. Type-I
kyphosis, the most common form, results from a partial failure of formation of
the anterior part of the vertebral body. This form has the greatest risk of
progression with growth and is associated with a 25% risk of anterior cord
compression if left
untreated1,4.
Type-II kyphosis results from an anterior failure of segmentation. The degree
of progression is related to the length of the anterior segmentation defect,
and this form of kyphosis is associated with a much lower risk of neurologic
compromise. Type-III kyphosis is the result of a combination of these
anomalies.
Acquired kyphosis at the thoracolumbar junction can develop following
extensive laminectomies performed for the treatment of tethered spinal cord
syndrome or spinal cord tumors, resulting in neurological dysfunction and
pain. Severe deformity often necessitates surgical correction, but such
treatment is complicated because of the proximity of the deformity to the
spinal cord, scarring from previous surgery, and the lack of adequate
posterior bone for fusion.
Treatment of congenital kyphosis is among the most challenging surgical
problems in the growing spine. Most deformities occur at the thoracolumbar
junction. This commonly results in a so-called trapped posterior hemivertebra,
the result of anterior failure of segmentation. The resulting growth imbalance
produces a varying degree of kyphosis and possibly scoliosis. The complexity
of the pathologic anatomy, its proximity to the spinal cord, the abundant
vascularity, and difficult access create a high risk of neurological injury
and inadequate correction with surgery.
A number of different options have been used for the treatment of
congenital kyphosis. Orthotic treatment is considered to be
ineffective2,3.
Surgery has been recommended, depending on the age of the patient and the type
and severity of the deformity. The standard surgical approaches for the
treatment of this deformity include posterior
arthrodesis1,5,6,
combined anterior and posterior
arthrodesis1,3,5,6,
and excision of the hemivertebra and arthrodesis with internal
fixation7-9.
Combined anterior and posterior arthrodesis is often recommended for the
treatment of severe deformities (those measuring
>55°)3,5,6.
Theoretically, excision of the hemivertebra would lessen the risk of
impingement on the spinal cord during correction of the deformity. However,
the posterior hemivertebra can be difficult to visualize during an anterior
procedure. There are no standard treatment recommendations for acquired
complex kyphoscoliosis because of the varied etiologies.
In 1894, Menard5
provided the first known description of the use of a costotransversectomy for
the treatment of a spinal abscess in a patient with tuberculosis. In 1956,
Seddon6 provided an
update on this technique in the era of modern spine surgery, again noting its
utility as a surgical approach to the spine. In 1995, Ahlgren and
Herkowitz7 described
a modified posterolateral approach to the thoracic spine and found it to be
valuable for the biopsy of spinal lesions, the decompression of paraspinal
infections, and the treatment of thoracic disc herniations.
Costotransversectomy approaches have been used extensively for a variety of
purposes, including the treatment of thoracic disc
herniations8, the
excision of spinal
neurinomas10, and
the excision of ventrally based space-occupying intraspinal
lesions11. Shono et
al.12 described a
similar procedure for resection of an isolated nonincarcerated hemivertebra
causing kyphoscoliosis. The procedure, which involved the use of a posterior
approach for hemivertebral excision followed by segmental spinal
instrumentation and arthrodesis, was associated with excellent results. In an
effort to improve visualization of the hemivertebra resection, Ruf and
Harms13 described a
posterior-only approach for excision of the hemivertebra combined with
immediate segmental pedicle screw fixation.
Treatment of acquired kyphoscoliotic deformities is challenging because
most patients with such deformities have had prior spinal surgery. A variety
of spinal disorders such as tethered-cord syndrome or spinal cord tumors
require laminectomy at the thoracolumbar junction, placing the patient at risk
for the development of thoracolumbar kyphosis.
In 1988, we began to use a posterior-only approach combined with a
posterior costotransversectomy for the treatment of congenital kyphosis and
acquired kyphoscoliosis. We used this modified approach to provide direct
visualization of the trapped nonincarcerated posterior hemivertebra, thereby
facilitating excision under direct visualization, or to allow for vertebral
resection and osteotomy followed by correction of deformity with use of
segmental spinal instrumentation. This approach provides excellent
visualization of the thecal sac during excision of the hemivertebra and
correction of the deformity, and it also provides sufficient exposure of the
adjacent anterior vertebral bodies for the performance of a supplemental
anterior arthrodesis through a single posterior approach. The purpose of the
present study was to report the results of this procedure in sixteen patients
with congenital kyphosis and acquired kyphoscoliosis.
We performed an institutional review board-approved retrospective
review of the records of the sixteen patients who had been managed at our
institution for the treatment of congenital kyphosis and acquired
kyphoscoliosis between 1988 and 2002. The mean age at the time of surgery was
twelve years (range, four to sixteen years). Nine patients were male, and
seven were female. The diagnosis was congenital kyphosis for fourteen patients
(including twelve who had a Type-I deformity, one who had a Type-II deformity,
and one who had a Type-III deformity). The remaining two patients had painful,
progressive kyphoscoliosis associated with previous extensive laminectomies
and failed surgical procedures for the treatment of tethered-cord sydrome. The
mean preoperative kyphotic deformity was 65° (range, 25° to 160°),
and the mean preoperative scoliotic deformity was 47° (range, 7° to
160°).
The clinical and radiographic characteristics of the sixteen patients are
summarized in Table I. Six
patients had no known associated spinal cord anomalies or other abnormalities.
The remaining ten patients had a variety of associated problems, including
tethered spinal cord that had been released prior to correction of the
kyphosis (three patients), developmental delay (two patients), seizure
disorder (two patients), neurogenic bladder or neuropathy (two patients), and
failed prior surgery (five patients). Three patients with myelodysplasia had
congenital kyphosis as the primary deformity. None of these patients had
typical congenital lumbar kyphosis of myelodysplasia.
In the absence of a validated tool for the assessment of the outcome of
spinal surgery in juvenile patients, we completed a subjective and
radiographic assessment of clinical outcome. In the course of our
retrospective review, a satisfactory outcome was achieved if the patient and
the family were satisfied with the results of the operation, there were no
obvious and clinically important postoperative complications, the fusion
appeared solid, and there was no evidence of hardware failure or progression
of deformity during the follow-up period. A fair outcome was achieved if a
clinically important postoperative complication was identified but the patient
did not require additional surgery. A poor outcome was defined as the need for
additional surgery for the treatment of a postoperative complication during
the follow-up period.
Operative Technique
The patient is positioned prone on a radiolucent operating table and is
carefully padded and stabilized to allow 30° of table rotation in both
directions around the central longitudinal axis. An attempt is made to
establish spinal cord monitoring of somatosensory evoked potentials. If
acceptable signals are present, they will later serve as confirmation of the
absence of spinal cord compression following correction. If acceptable signals
cannot be initially obtained as a consequence of preexisting neurologic
abnormalities or prior spinal cord surgery, correction of the deformity is
accomplished with an additional degree of caution and the adequacy of
decompression is confirmed visually. If somatosensory evoked potentials are
not obtainable, a wake-up test is performed intraoperatively after correction
and instrumentation of the deformity in patients with normal motor function.
The back is prepared and draped widely out to the posterior axillary line. A
standard midline longitudinal incision is made as needed to treat the
deformity. A subperiosteal posterior exposure of the spine is then completed,
with the surgeon bearing in mind that the posterior elements may be absent or
abnormal in terms of their appearance or thickness or their relationship to
adjacent segments.
Fluoroscopy is used to identify the level of the hemivertebra and its
associated pedicle, lamina, transverse process, and attached rib. A transverse
incision is then made through the paraspinous muscle mass; the incision is
centered at the level of the hemivertebra. The adjacent ribs are exposed
subperiosteally for approximately 3 cm. For adequate exposure and a
sufficiently large operative field, it usually is necessary to resect two ribs
at the level of the anomalous vertebral body. Very small hemivertebrae can be
removed following the resection of a single rib, whereas the size of the
orientation of other anomalous segments requires the resection of as many as
three ribs. This decision is made intraoperatively, depending on the extent
and complexity of the deformity. Rib resection is usually unilateral and is
done on the apex of an associated scoliotic curve. Care is taken to preserve
the pleura during rib resection, and a blunt retractor is placed with the tip
at the anterior aspect of the vertebral body to define the deep and lateral
aspects of the surgical field. If a pleural tear occurs during rib removal, a
repair is attempted and the placement of a chest tube is obligatory. Next, the
lamina and the pedicle of the hemivertebra are removed, with care being taken
to preserve the segmental nerve at that level. The superior and inferior
exiting nerve roots are visualized or palpated in order to ascertain their
course in the surgical field and to protect them during exposure and removal.
A laminectomy at the level of the hemivertebra allows for direct visualization
of the dura and intraspinal contents, which are protected, and for hemostasis
of the paraspinal venous plexus. This provides excellent visualization of the
dural sac and allows gentle retraction and protection during resection of the
hemivertebra. The discs and end plates of the body of the hemivertebra are
dissected in a subperiosteal fashion and are removed first because they form
identifiable anatomic planes for dissection and are relatively avascular
compared with the vertebral body itself. Once the hemivertebra has been
defined by removal of the superior and inferior intervertebral discs, it is
resected as completely as possible. The posterior longitudinal ligament is
resected with the posterior portion of the body, and the resection is carried
as far anteriorly as possible while preserving the anterior longitudinal
ligament.
The anomalous pattern of segmental vascularity that often accompanies these
deformities can make adequate hemostasis difficult to achieve and often is
responsible for the substantial blood loss that is encountered during the
procedure. Gaining control of a bleeding vessel at the deep limit of the
surgical field often requires a combination of adequate aspiration, bipolar
cautery, thrombin-soaked gel foam, direct pressure, and time. Once the
hemivertebra has been removed, the adjoining end plates are denuded to expose
cancellous bleeding bone. A wedge that approximates the desired amount of
correction is created in the anterior column, with care being taken to
preserve the anterior longitudinal ligament so that it serves as a rotational
hinge and stabilizing restraint to translation during correction. The resected
hemivertebra is morselized for bone graft and is placed loosely in the
anterior aspect of the gap left by the resection. For patients with acquired
kyphoscoliosis without an associated hemivertebra, a decancellation
osteotomy14 of the
apical vertebra is performed under direct visualization.
Following resection of the hemivertebra, posterior spinal instrumentation
is placed for correction of the deformity. The pattern of fixation that is
used depends on the type of the deformity and the preference of the surgeon.
Our current preference is to use pedicle screws at least two vertebrae caudad
to the level of the resection and a combination of pedicle screws and hooks
cephalad to the level of the resection, depending on the specific deformity
and the ease of pedicle navigation. Given the relative ease of placing pedicle
screws inferior to the deformity, we typically begin by inserting pedicle
screws at the inferior limit of the instrumentation. We then proceed
superiorly with pedicle screw fixation until the superior limit of the
instrumentation is reached or the difficulties of pedicle navigation warrant a
switch to pedicle, lamina, or transverse process hooks, as appropriate.
Fluoroscopy is used to confirm satisfactory placement of the fixation points.
Two rods are contoured to approximate the desired amount of correction and are
attached to the inferior points of fixation. A combination of cantilever
bending and translation forces are then applied, and the deformity is slowly
corrected to approximate the normal sagittal and coronal balance of the spine.
During this process, the dura and its contents can be directly inspected for
signs of compression by visualizing and palpating the anterior aspect of the
thecal sac at the level of the hemivertebra and the apex of correction. If
compression of the thecal sac or neural elements does occur with correction of
the overall deformity, additional bone can be resected at the point of
compression if it can be seen or palpated. If there are changes in
somatosensory evoked potentials during correction and there is not an obvious
source of compression, the etiology of the compromise is thought to be
vascular and the rods are recontoured to reduce the amount of correction. With
a combination of these maneuvers, the deformity can be corrected without
compromising the contents of the spinal canal.
A standard posterior spinal arthrodesis is then completed
(Figs. 1-A and 1-B). Our
preference is to use local autogenous bone and supplemental morselized
allograft bone. A surgical drain with a closed self-suctioning reservoir is
placed, a chest tube is placed into each hemithorax that has been violated by
a pleural opening, and the wounds are closed in a routine fashion. The patient
is mobilized with the assistance of a physical therapist on the first or
second postoperative day, depending on the comfort level. An orthosis was not
used postoperatively for any patient in the present series. Specific activity
restrictions that avoid bending, twisting, heavy lifting, and sporting
activities are maintained for six months.
All sixteen patients were managed with vertebral resection through a
simultaneous anterior and posterior approach to the spine that involved a
single posterior midline incision and a costotransversectomy. All but one of
the patients had an anterior and posterior spinal fusion and posterior
segmental spinal instrumentation; the remaining patient was too small for
spinal instrumentation at the time of vertebral resection. The mean correction
of the major kyphotic deformity was 31° (range, 0° to 82°), and
the mean correction of the major scoliotic deformity was 25° (range,
0° to 68°). The mean duration of follow-up was 5.0 years (range, 2.0
to twelve years).
Four patients had a major complication. One patient had a failure of
posterior instrumentation that necessitated revision surgery, one patient had
development of persistent lower extremity dysesthesias of uncertain etiology,
and two patients had radiographic evidence of late progression of pelvic
obliquity caudad to the fusion. There were no substantial neurological
injuries affecting bowel or bladder function or muscle strength in the lower
extremities.
Thirteen patients had a satisfactory outcome; that is, both the patient and
the family were satisfied with the results of the operation, there were no
obvious and clinically important postoperative complications, the fusion
appeared solid, and there was no evidence of hardware failure or progression
of deformity during the follow-up period. Two patients had a fair outcome;
that is, they had a substantial postoperative complication but did not require
additional surgery. One patient had a poor outcome because additional surgery
was needed for the treatment of a postoperative complication during the
follow-up period. Specifically, a catastrophic failure of the initial
posterior instrumentation necessitated revision anterior and posterior surgery
for stabilization. Despite this additional surgery, the patient believed that
the overall outcome was satisfactory; nevertheless, the result was rated as
poor because of the need for a second major surgical procedure.
The natural history of congenital kyphosis has been well described
in the
literature1-3,15,16.
Although less common than congenital scoliosis, congenital kyphosis is
associated with a greater risk of anterior cord compression and neurologic
compromise with growth and progression of the deformity if left
untreated16. Early
intervention to prevent progression of the deformity and to allow for some
correction with growth is currently
recommended3,16.
In a review of ninety-four patients in whom progressive congenital kyphosis
had been treated after the age of five years, Winter et
al.3 recommended a
posterior arthrodesis for curves of =50° and a combined anterior and
posterior arthrodesis for curves of >50°. McMaster and
Singh16 also
recommended that all children with Type-I or III congenital kyphosis should be
managed with posterior arthrodesis without instrumentation before the age of
five years and before the kyphosis exceeds 50°. In this group of younger
patients, the authors reported that posterior arthrodesis alone resulted in a
mean correction of 15° with growth, from a mean preoperative deformity of
43°. Among patients who had been managed with posterior arthrodesis
without instrumentation alone, with and without cast application, at the age
of six years or more, there was limited correction of only 9° from a mean
preoperative deformity of 70°, and there was a substantial rate of
pseudarthrosis or kyphosis progression during the follow-up period (mean, 6.6
years). The authors recommended anterior release, strut-grafting, and
posterior arthrodesis with instrumentation (if possible) for these older
patients and for patients in whom the curve exceeds 60°.
Kim et al.15
noted that correction of kyphosis may occur with continued growth in patients
with Type-I and III deformities, especially when a posterior arthrodesis is
performed when the patient is two years old or less. In their study of
twenty-six cases of surgically treated congenital kyphosis and kyphoscoliosis,
a variety of surgical techniques were used. Five patients with a mean age of
sixteen months underwent posterior arthrodesis without instrumentation alone,
with improvement of the mean kyphotic deformity from 49° to 26°.
Pseudarthrosis developed in two patients, necessitating subsequent posterior
augmentation or anterior arthrodesis. Five patients with a mean age of 13.6
years underwent posterior arthrodesis with instrumentation, with improvement
of the kyphotic deformity from 59° to 29°. Seven patients with a mean
age of sixteen months underwent anterior release or vertebral resection
followed by posterior arthrodesis, with improvement of the kyphotic deformity
from 48° to 22°, whereas nine patients with a mean age of 11.5 years
demonstrated improvement from 77° to 37° after the same procedure. The
authors did not report the amount of intraoperative blood loss. They did not
comment that spinal instrumentation reduced the need for subsequent
augmentation of the fusion and was associated with a low prevalence of
pseudarthrosis. Two of the twenty-six patients in that study had development
of a postoperative neurological deficit, and the authors identified a number
of risk factors for neurologic injury: an older age at the time of correction,
combined anterior and posterior arthrodesis procedures, more severe deformity,
and preexisting spinal cord compromise.
The studies by McMaster and
Singh16, Winter et
al.17, and Kim et
al.15 suggest that
whereas early posterior arthrodesis is effective in the younger child, it is
not sufficient for the older child who presents with congenital kyphoscoliosis
and a substantial deformity. The deformities that arise in older children as a
consequence of an abnormal hemivertebra present a difficult surgical
challenge. Some degree of vertebral resection often is required in order to
achieve satisfactory correction of the deformity, and this is not possible
through a posterior-only exposure and fusion. A combined anterior and
posterior arthrodesis for the treatment of kyphoscoliosis has inherent
limitations. With use of separate approaches, it is not possible to expose and
resect the hemivertebra from the anterior side, to perform spinal
instrumentation, and to observe the effects of posterior correction on the
contents of the spinal canal during surgery. The adequacy of the anterior
decompression must be estimated prior to closing the anterior incision and
proceeding to the posterior approach for instrumentation and correction of the
deformity. This limitation can be overcome by performing a surgical resection
of the hemivertebra and correction of the deformity through the same posterior
approach. While a posterior-only approach for resection of the hemivertebra
seems to be technically challenging and fraught with risk to the neural
elements, several published reports have described acceptable clinical
outcomes in association with this
technique12,13.
Increasing familiarity with anterior and posterior column surgery through a
posterior approach has resulted in a tendency to fuse both columns at a
younger age. For example, Ruf and
Harms18 recently
reported on twenty-eight consecutive cases of congenital scoliosis in very
young children who underwent hemivertebra resection through a posterior-only
approach at a mean age of 3.3 years. We concur with their conclusions that
this procedure permits excellent correction in the frontal and sagittal planes
and produces a short-segment fusion that allows for normal growth in the
unaffected parts of the spine, and we add that it also avoids the
uncertainties associated with unbalanced growth of the anterior column that
may lead to progression, recurrence, or crankshaft-type deformities.
The location of a typical hemivertebra makes it amenable to resection from
the posterior approach. The anomalous vertebral body is located at the apex of
the kyphosis, and several authors have reported excellent visualization of the
hemivertebra during resection from a posterior approach. In addition, the
surgical dissection required to remove the hemivertebra exposes the neural
elements that are at risk of compression during correction of the deformity.
It should be noted that substantial blood loss should be anticipated during
this procedure. We speculate that large losses of blood are a result of the
combination of an anomalous vascular supply to the hemivertebra, exposure of
the cancellous surfaces of end plates of the adjacent vertebral bodies, and
the technical difficulty of obtaining hemostasis in the depths of the
operative field.
Shono et al.12
recently reported the results of one-stage posterior hemivertebra resection
and posterior segmental spinal instrumentation in a study of twelve patients
with congenital kyphoscoliosis who were between eight and twenty-four years of
age. The procedure was associated with satisfactory correction of both the
scoliosis (from 49° to 18°) and the kyphosis (from 40° to
17°). The authors reported no postoperative neurologic complications, a
100% union rate, and a mean blood loss of 600 mL. They commented that
visualization of the pathologic hemivertebra was enhanced by removal of the
adjoining rib. This approach was thought to be safe and effective for
adolescents with congenital kyphoscoliosis, and the authors concluded that the
single-stage posterior approach was effective for resection of an isolated
hemivertebra in the thoracic and lumbar spine. Ruf and
Harms13 described a
similar approach for hemivertebra resection in a study of twenty patients
ranging from less than two years of age to fourteen years of age. The
approach, which emphasized limited segmental fixation with use of pedicle
screws, was associated with correction of the scoliotic deformity from 41°
to 14° and correction of the kyphotic deformity from 24° to 11°.
Again, the authors were able to achieve excellent visualization of the
hemivertebra as well as of the effects of correction of the deformity on the
adjacent neural structures. The mean blood loss was 635 mL. In a subsequent
report on patients who were five years of age or
less18,
twenty-eight children with a mean age of 3.3 years were managed with a
posterior-only approach with transpedicular instrumentation. The mean
scoliotic deformity was corrected from 45° to 13°, and the mean
kyphotic deformity was corrected from 22° to 10°. The authors reported
no neurologic complications, one infection, three cases of implant failure,
and a mean blood loss of 496 mL.
Two patients in the present series were treated for acquired
kyphoscoliosis. Both had had extensive, repeated laminectomies for the
treatment of tethered-cord syndrome and subsequently had had development of
progressive, painful kyphoscoliosis at the thoracolumbar junction. Neither
patient had undergone instrumentation and fusion at the time of the
laminectomies. The use of the costotransversectomy approach following the
failure of previous surgery allows for excellent visualization of the spinal
cord during correction of the deformity.
In conclusion, we believe that congenital kyphosis and acquired
kyphoscoliosis can be safely corrected with use of a one-stage posterior
approach to the spine. The addition of a costotransversectomy approach to the
anterior part of the spine allows excellent visualization during resection of
a hemivertebra and also allows access to the anterior column for fusion, but
substantial blood loss should be anticipated. We recommend arthrodesis of the
entire deformity and stabilization with use of pedicle fixation where
possible. ?