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MANAGEMENT – continued
Transpedicular Screw Fixation
Targeting the lumbar region for
correction has its advantages as were mentioned, but when desired
curvature is ascertained and proper line of gravity is obtained
the rest of the spine takes on a shape that is more structurally
and functionally correct. Although plaster jackets and shells
attempt to address such concerns, the nuisance of prolonged rehabilitation
and risk of succumbing to previous malalignment does exist. Therefore,
surgeons are constantly attempting to reduce postoperative discomfort
and risks by internal stabilization of the spine in the desired
posture. However, such instrumentation has been known to loosen
or break, new advances are constantly being sought.
Since 1979, Puschel and Zielke
implemented the Harrington compression system for posterior multilevel,
four to six segments, osteotomy. (35)
In 1982, Puschel and Zielke reported their experience of (14) AS individuals
with such instrumentation. (35)
Although promising, the Harrington compression system did not
adequately provide harmonic relordosation and continued to pose
a risk of sharp angled monosegmental extension osteotomy. (21, 30, 35)
As a result, transpedicular screw –rod fixation was introduced
which facilitated relordosation, decreased mortality, decreased
neurologic compromise, and decreased the risk of sharp angled
monosegmental extension osteotomy.(5,
23,30,34,41)
In 1990, Hehne, Zielke, and Bohm
reported on the outcome of 177 AS patients who underwent polysegmental
lumbar osteotomies with transpedicular screws. (20)
Hehne et al performed a similar osteotomy as Smith–Petersen
et al at T12 or L1 to L4. Following the osteotomy, transpedicular
screws are placed between T9–S1. Hehne et al positioned
the screws at the crossing of the axis of the transverse process
and joint line. Screw direction was at 15 degrees to the midline
and was not pushed through the anterior cortex of the vertebra.
Closing of the osteotomy was accomplished through slow straightening
of the table while tightening the nuts on the screws. Postoperatively,
a plaster cast was worn for four months followed by wearing a
Stagnara brace for an additional four months.
Complication rate was minimal
with 77.4% reporting no complications. Seventy–seven percent
presented no complications, complications were reversible in
18%, 7% required reoperation, and four patients died of causes
not related to the procedure. The average correction was 44 degrees
which translates to a gain of 9.5 degrees per segment and a 7
degree or 15 degree loss of correction at final examination.
Back pain improved, no evidence of pseudoarthrosis was present,
progressed kyphosis above the instrumentation did not occur,
and all patients achieved solid bone fusion eight months postoperative.
Hehne et al also found that patients exhibited a loss of lower
thoracic correction after a period of three years. As a result,
Hehne et al recommended application of internal instrumentation
to be applied at T9 – S1.
Posterior Wedge Osteotomy
with Vertebral Corpectomy
One of the first to propose a
posterior wedge osteotomy approach with dorsal partial vertebral
corpectomy was Thomasen in 1985. (42)
Thomasen reported a similar procedure performed by Scudese and
Calabro in 1963. (36)
Thomasen noted the results of eleven patients who underwent his
procedure and who achieved 12–50 degree correction. The
procedure consisted of the patients in a prone position with
endotracheal anesthesia. The vertebral segment of choice was
L2. A midline incision was made at T11–L4 and subsequent
spinous muscle retraction of L1–L4. A posterior wedge 5
cm broad osteotomy followed to remove the tip of the L2 spinous
process and the superior portion of L3 spinous process. The osteotomy
also consisted removal of L2's pedicles, laminae, transverse
processes, superior articular processes, and the removal of the
upper portion lamina of L3. As a result, the nerve roots and
dural space were exposed and liberated. With caution, an osteotome
was used to resect the posterior wall of the vertebra (Fig.
6). A ronguer was then implemented laterally to remove spongy
vertebral bone which produced bleeding and necessary steps to
establish hemostasis followed. Moreover, dura was stripped from
adjacent laminae. By manual and operative table manipulation,
the spine was extended and a compression fracture was created
at the L2 vertebra and the osteotomy was closed (Fig.
7). A plaster jacket was worn for 3 months. Thomasen also
applied plates and metallic wires posteriorly in some patients
to facilitate stability and fusion. Patients reported a positive
outcome. Thomasen's method has gained popularity because there
is decreased stretch of the cauda equina, aorta, and intraabdominal
muscles which could complicate the outcome.
Thomasen Pedicle Subtraction
Method with Transpedicular Screw –Rod Fixation
Although many have contributed
possible avenues for correction of lumbar fixed deformity in
AS, the spine author's preference is a combined monosegmental
Thomasen osteotomy and transpedicular screw – rod fixation.
(23,44)
The patient is positioned prone and a midline incision at the
spinous process is performed between the levels of T12–L4.
After necessary paraspinal and spinous muscles are reflected,
transpedicular screws are inserted at T12, L1, L3, and L4 (Fig. 8). The screws
positioned centrally, are inserted parallel to the superior end
plate, converge towards the midline, and directed towards the
anterior vertebral cortex without complete penetration. Afterwards,
a posterior V–shaped wedge osteotomy, as Thomasen reported,
is performed at the L2 vertebral segment and H frame rods are
positioned over the pedicled screws (Fig.
9). The osteotomy is closed by table extension and manual
leg elevation slowly while compressing the fixation device. The
patient is then placed in a TLSO immobilizer for 12 weeks.
The spine author has found this
method beneficial in correcting fixed lumbar deformity in AS.
Lumbar correction is achieved providing the patient with a more
erect posture, increased horizontal gaze, increased pulmonary
function, subsidence of pain, and a more physically acceptable
appearance (Fig.
10). Due to the nature of the osteotomy, the neural structures
are visible which aid the physician to avoid peripheral neural
compression when closing the osteotomy site. Since partial removal
of the L2 vertebral body is accomplished, no elongation of the
anterior column occurs which could pose a threat to proximal
vascular and neural structures. The intact anterior longitudinal
ligament and the anterior cortex of the vertebra act as hinges
which provide sound fusion of the remaining rich vertebral cancellous
bone and posterior segments. Furthermore, the use of transpedicular
screw fixation prevents displacement, provides solid stability
and sagittal correction, increases proper bone fusion, and decreases
the wear of external orthosis (Fig.
11 A,B). (16,20,21,23,34,35,44)
Complications
With mortality rates as high
as 10 %, (12,27,28,29,30)
the search to decrease complications is priority. Although new
innovations and technique refinement have decreased the risk
of death, (16,20,23,44) the
threat of neurological compromise and vascular and pulmonary
complications should be omnipresent. In 1956 Lichtblau and Wilson
first reported possible causes for aortic rupture in correction
of AS. (32)
Lichtblau and Wilson mentioned a case where a 35 year old male
under general anesthesia underwent osteotomy at three levels.
The aorta was not fully calcified and presumably when the adjacent
calcified anterior longitudinal ligament ruptured, after the
vertebra was separated at the intervertebral disc, the aorta
did not give and the patient died. Further cases were also reported
by Klems and Fried in 1971 (25)
and Weatherley et al in 1988. (47)
Weatherley et al reported two cases of aortic rupture due to
lumbar extension osteotomy. In both cases, the patients developed
a retroperitoneal hematoma and developed signs of cardiovascular
collapse which led to death. Moreover, Camargo et al also reported
a case where aortic rupture occurred on the ninth postoperative
day. (12)
Further manifestations of AS
could pose complications during surgery. An aspect of the inflammatory
response in AS is the fibrosis of cardiac vessels and the aorta.
As a result, the aorta weakens and is more prone to rupture from
aneurysms . Cardiac conduction is also affected causing arrhythmia
due to fibrosis invasion of the myocardium. Also, cardiomegaly
is known to occur and angina (7)
Furthermore, pulmonary fibrosis could occur in the upper lobe
and could lead to edema.
Intraoperative methods of anesthetization
could manifest complications. Due to the abnormal cervical kyphotic
curvature that results in patients with progressed forms of AS,
intubation for general anesthesia is difficult and could generate
respiratory complications. (1,26,37) As a
result of intubation, patients with a severely kyphotic cervical
spine are unable to cough postoperatively and accumulate mucus
in their respiratory tract. Moreover, progressed AS patients
suffer from pulmonary restriction. Thus, positioning the patient
on the operating table needs careful attention. (1,5,19,23,26,37,44)
Complications could also arise
from elongation of the anterior column. Elongating the anterior
column could stretch the superior mesenteric artery over the
duodenum which leads to gastric dilation. (37)
As a result, patients are prone to vomit and if intubated encounter
further obstruction. Moreover, vascular vessel elasticity could
develop thrombosis (28)
not to mention aortic rupture. (12,25,32,47) Furthermore,
neurologic compromise could result in the form of neuropraxia
or paraplegia (5,20) from spinal cord compression as a result
of insufficient bone removal, (44)
subluxation, (22)
and impingement. In addition, retrograde ejaculation is also
considered a risk. (40,46)
Further complications also are
present. Instrumentation failure could develop from improper
application or failure to tighten properly for compression. (16,20,34,44,46) Furthermore,
shock, (28)
amyloidosis, (28)
pneumonia, (22)
pulmonary embolism (22,34) deep wound
infection, (20,34) dural leak,
(16,34,41) deep
venous thrombosis, (5)
nonunion (46)
and over correction could also surface.
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