Keywords pedicle subtraction osteotomy - kyphosis - spinal tuberculosis - four-rod technique
- postoperative complications - thoracolumbar spine
Palavras-chave osteotomia de subtração pedicular - cifose - tuberculose da coluna vertebral - técnica
das quatro hastes - complicações pós-operatórias - coluna toracolombar
Introduction
Pedicle subtraction osteotomy (PSO) is a powerful tool for the management of sagittal
misalignment, and it can restore angular sagittal alignment up to 30° to 40°.[1 ] However, rod breakage after PSO is common, occurring in 15.8 to 25% of patients
who undergo this procedure.[2 ]
[3 ]
[4 ]
[5 ]
[6 ]
[7 ] Most of these instrumental failures (89%) occur at the index level vertebra or in
adjacent vertebras. Furthermore, 71% of rod breakages happen in the first 12 months
after the corrective surgery.[5 ] Gupta et al (2017)3 reported the use of a 4-rod technique in lumbar PSO for the treatment of adult spinal
deformities that had considerably reduced the rate of rod breakage.
The aim of the present study is to present the case of a patient with late thoracolumbar
(TL) junction hyperkyphosis secondary to spinal tuberculosis that was successfully
managed with PSO followed by four-rod technique stabilization.
Case Report
A 64-year-old woman was referred with severe mechanical low back pain that progressively
increased mainly over the previous 6 months, and that was associated to pain in the
buttocks and posterior thighs, without radicular trajectory. She was unable to stand
or walk for more than 20 minutes. Ten years before she had been treated for spinal
tuberculosis (also known as Pott disease) in the TL junction according to the Brazilian
guidelines, with successful remission.[8 ]
Neurological Examination
The patient presented a forward trunk shift while standing or walking, and a TL junction
kyphosis on inspection. On palpation, there was severe and painful paravertebral muscle
contracture in the thoracic and lumbar regions. She reported severe back pain during
assisted lumbar extension or rotation that was more intense in the lumbar region rather
than in the apex of the deformity. The neurological examination was normal, except
for bilateral hypoactive Achilles tendon reflexes. The Oswestry disability index (ODI)
was of 32%, a finding compatible with moderate disability. The Short-Form Health Survey
36 (SF-36) physical and mental scores were 0 and 40 respectively.
Diagnostic Imaging
The computed tomography (CT) of the lumbar spine revealed TL kyphosis, with a wedge-shaped
L1 vertebral body and sclerotic bone from T10 to L3 ([Fig. 1b ]). Narrowing of the spinal canal was observed at L1 and L2 by CT and magnetic resonance
imaging (MRI), which also showed conus medullaris and cauda equina encroachment ([Fig. 1b-e ]). Scoliosis radiographs displayed a short-angle kyphosis with apex at L1 (T12L2
Cobb angle = 34°), thoracic hypokyphosis (T4T12 Cobb angle = 22°) and lumbar hyperlordosis
(L1S1 Cobb angle = 69°). The spinopelvic parameter values were: pelvic incidence,
48°; pelvic tilt (PT), 13°; sacral slope, 35°; and sagittal vertical axis (SVA), +1 cm
([Table 1 ]; [Fig. 2a ] and [c ]). Surgical treatment was indicated due to refractory mechanical back pain secondary
to TL hyperkyphosis and associated with lumbar hyperlordosis. Informed consent for
the procedure was obtained from the patient.
Fig. 1 A 64-year-old female was diagnosed with Pott disease and treated conservatively.
The lumbar spine magnetic resonance imaging (MRI) exam – T2 sequence – shows a hypointense
signal at L1 and L2 (a). Ten years later, the computed tomography (CT) and the MRI
(b, c, d and e) show thoracolumbar (TL) junction kyphosis, bone sclerosis from T10
to L3, and spinal canal narrowing.
Fig. 2 Preoperative standing radiographs (a and c) show short angular kyphosis with apex
at L1 (Cobb angle: 34°) and normal sagittal vertical axis (SVA). After pedicle subtraction
osteotomy (PSO) at L1 using 4-rod fixation, the thoracolumbar (TL) transition angle
was restored (Cobb angle: 11° at the 2-year follow-up), and the compensatory thoracic
hypokyphosis and lumbar hyperlordosis were solved.
Table 1
Preoperative, Postoperative and Follow-Up Values of the Sagittal Balance Parameters
Sagittal balance parameter
Preop
6 months po
12 months po
24 months po
T4-T12 thoracic kyphosis (o )
+22°
+41°
+43°
+40°
T12-L2 angle (o )
+34°
+3°
+6°
11°
L2-S1 lumbar lordosis (o )
−69°
−57°
−55°
−58°
Sagittal vertical axis (cm)
+1
+1
+1
+1
Pelvic tilt (o )
13°
−
10°
8°
Abbreviations: po, postoperative; preop, preoperative.
Surgical Technique
The patient underwent an L1 PSO and spinal stabilization with the four-rod technique.
Positioning. After induction of general anesthesia, the patient was placed in prone position.
Intraoperative neurophysiological monitoring (IONM) was not used.
Exposure. Through a midline incision, the paraspinal muscles were dissected subperiosteally
from the spinous processes to the tip of the transverse processes from T9 to L4.
Instrumentation. The pedicle screws were inserted four levels above and three levels below the wedge
vertebra (L1) under the guidance of fluoroscopy. In T9, T10, T11, L3 and L4, the entry
points were in the superior facets. In T12 and L2, the entry points were in the mammillary
processes, and their trajectories were of 22° to 30° medial to the sagittal plane,
rather than the usual 0° to 10° at these levels. Thus, the screw heads of the levels
adjacent to L1 were more lateral and slightly deeper than the cranial and caudal ones
([Fig. 3d ]).
Fig. 3 Pedicle screws were inserted 4 levels above and 3 levels below the wedge vertebra
(L1). In T12 and L2, the entry points were lateral at the junction of the superior
facet and transverse processes (a). Pedicle subtraction osteotomy (PSO) was performed
at the apex (L1) of the kyphosis and closed with bilaterally alternating compression
maneuvers over the screw heads of T12 and L2, fixed with short rods. Final stabilization
was obtained with long rods (c, d and e).
Pedicle subtraction osteotomy. The osteotomy was performed at L1 as previously described.[9 ]
[10 ] The posterior elements of L1, including the pedicles and transverse processes, were
removed, as well as the spinous process and the caudal half of the T12 lamina. The
nerve roots of T12 and L1 were exposed bilaterally. Finally, a partial wedge resection
of the posterior vertebral body of L1 was performed mainly with osteotomes, and completed
with rongeurs and a drill. In this step, the fluoroscopy was paramount to delineate
the directions of the osteotomes, as well as the angle of the bone fragment to be
removed ([Fig. 3a ] and [b ]; [Fig. 4a ]). Incidental durotomy occurred, but it was promptly sutured. The disks above and
below remained intact. Before the closing procedure, a temporary rod was used to avoid
translation in one side when the other side of the osteotomy was done.[11 ]
Fig. 4 Schematic illustrations of pedicle subtraction osteotomy (PSO) and four-rod technique
stabilization to treat thoracolumbar hyperkyphosis. First, the pedicle screws are
placed, then the posterior arches of T12 and L1, as well as the L1 pedicles, are removed;
finally, the PSO is performed (a). Compression maneuver over the T12 and L2 screws
heads to close the bone defect and correct the hyperkyphosis, followed by short rods
locking, and then long-rod fixations (b and c). Posterior 3D image showing the final
aspect of the instrumentation (d).
Kyphosis correction. Closure of the osteotomy was performed by bilateral alternating compression maneuvers
over the screw heads of T12 and L2, fixed with short rods ([Fig. 3c ]; [Fig. 4b ] and [c ]). During the PSO, hemostasis with bone wax was avoided on the bone defect surfaces
to prevent pseudarthrosis. Subtle compression of the left L1 nerve root was noticed
soon after the osteotomy closure, and decompression was readily performed.
Stabilization, grafting and closure. Final stabilization was obtained with long titanium rods (6.0 mm) and caps inserted
and tightened from T9 to L4, with satisfactory correction of the TL junction kyphosis.
After decortication, local bone grafts were placed posterolaterally. To stiffen the
construct, cross-links were used to connect the long rods to one another and to connect
the short rods to the long ones ipsilaterally. Intraoperative fluoroscopy showed adequate
placement of implants and correction of TL kyphosis ([Fig. 3c ], [d ] and [e ]; [Fig. 4c ] and [d ]). Intrawound vancomycin powder (2 g) was used.[12 ]
[13 ]
[14 ] The wound was closed in layers, and a closed suction drain was left in place for
48 hours. The operating time was 515 minutes, and the patient received a packed red
blood cell transfusion (950 mL).
Follow-up
The length of stay of the patient in the hospital was of 5 days. The patient presented
bilateral meralgia paresthetica despite the protection of the iliac crests with cotton
paddles. A TL vest was not recommended. Sixteen days postoperatively, she complained
of moderate back pain and severe meralgia paresthetica, without motor function compromise.
An examination revealed a superficial wound infection with no fluid leakage, which
was solved with oral antibiotics for 3 weeks. The pain was treated with pregabalin
(150 mg per day) for 6 months, and codeine (30 mg every 4 hours as needed).
Radiological Outcomes
Standing scoliosis radiograph images 6, 12 and 24 months after the procedure showed
normal sagittal alignment parameters, without compensatory mechanisms and no signs
of pseudarthrosis or implant failure ([Table 1 ] and [Fig. 2 ]). Considerable improvements were observed in the thoracic kyphosis (+22° versus
+40°) and lumbar lordosis (−69° versus −58°) when the images obtained 24 months after
the surgery were compared with the preoperative images ([Table 1 ], [Fig. 2 ]).
Clinical Outcomes
Six months postoperatively, the patient reported considerable improvement in both
back pain and meralgia paresthetica, with sporadic use of analgesic drugs. Self-reported
outcome questionnaires showed significant improvement at 6 months, which was maintained
12 and 24 months postoperatively. At the final follow-up, she reported considerable
spine pain relief and increase in quality of life, despite feeling unilateral hip
joint pain, which was managed conservatively ([Table 2 ]).
Table 2
Clinical Assessment by Self-Reported Outcome Questionnaires: Preoperative, 6 Months
and 12 Months Postoperatively
Parameter
Evaluation period
Preop
6 months po
12 months po
24 months po
SF-36 (physical)
0
100
100
75
SF-36 (mental)
40
84
84
84
ODI
32%
0%
18%
6%
Abbreviations: ODI, Oswestry disability index; po, postoperative; preop, preoperative;
SF-36, Short-Form Health Survey 36.
Discussion
Thoracolumbar hyperkyphosis may cause sagittal misalignment, which is characterized
by a forward dislocation of the body's gravitational center that elicits compensatory
mechanisms, mainly thoracic hypokyphosis and lumbar hyperlordosis due to paravertebral
muscle contractures, resulting in increased energy expenditure and chronic back pain.[15 ]
[16 ]
[17 ]
[18 ]
[19 ] Secondary trunk extension also overloads the facet joints, resulting in a painful
condition as well.[17 ]
[19 ]
[20 ] Thus, restoration of the sagittal alignment counteracts this process and relieves
discomfort.[21 ]
The reported case showed hyperkyphosis at the TL junction, the most common site affected
by spinal tuberculosis.[22 ]
[23 ]
[24 ] According to the global alignment concept, the patient had hidden sagittal imbalance , as shown by the thoracic hypokyphosis (+22°), and lumbar hyperlordosis (−69°), which
was associated with a preoperatively balanced pelvis (sagittal vertical axis (SVA): 1 cm; PT: 13°).[25 ]
Surgery is best indicated when there is significant pain associated with a kyphotic
segmental deformity exceeding 20°.[26 ] Surgical treatment is also recommended if there is progressive neurological deficit
secondary to canal encroachment and/or spinal cord tethering at the apex of the kyphosis,
usually in the thoracic spine.
Different types of osteotomy might be necessary to treat hyperkyphosis.[1 ]
[9 ] The decision about which osteotomy to use depends on the anatomy of the lesion,
the amount of angular correction needed to restore global spine alignment, and the
type of curve (long or short). Ponte osteotomies (Schwab 2) at multiple levels allow
corrections of 5° to 10° per level, and are recommended mainly for long kyphotic curves.
A PSO, with or without superior diskectomy (Schwab 4 and 3 respectively), enables
corrections of 30° to 45°, and is indicated to address short-angle hyperkyphosis.[1 ]
[9 ]
[27 ]
[28 ]
[29 ]
[30 ]
[31 ] However, in cases of severe kyphosis, mainly higher than 60°, vertebral column resection
might be needed.[32 ]
[33 ]
[34 ]
[35 ]
[36 ]
[37 ] Thus, through a single posterior approach, a three-column osteotomy (PSO or vertebral
column resection [VCR]) may enable the correction of sagittal misalignment in pathologies
such as posttraumatic kyphosis, postinfection kyphosis, congenital deformities, adult
spinal deformities, ankylosing spondylitis, and iatrogenic flat back.[17 ]
Gupta et al (2017)3 have described a new 4-rod technique in which all rods are connected to pedicle screws
in cases of lumbar PSO (L2, L3 and L4) for the treatment of adult spinal deformities.
The two short rods are used to stabilize the superior and inferior vertebras that
are adjacent to the osteotomy level. The two other rods connect the remaining levels
involved in the instrumentation (holding rods). None of the 29 patients treated with
the Gupta technique experienced rod breakage during a 5-year follow-up. In comparison,
the 4-rod technique decreased the rate of implant failure after PSO from 25% to 0
during a 5-year follow-up (p = 0.008; Gupta et al, 2017).[3 ]
In the TL junction, PSO has been successfully used to correct posttraumatic kyphosis
as well as Pott-disease deformities. Significant improvement in clinical outcomes
has been achieved after PSO for the treatment of TL hyperkyphosis secondary to tuberculosis,
a result that has been related to hyperkyphosis correction and restoration of normal
sagittal alignment.[29 ]
[33 ] In the present case we used the 4-rod pedicle-based technique to stabilize a short-angle
TL kyphosis after L1 PSO.
Pseudarthrosis and implant failures (mainly rod breakage) are frequent complications
after a PSO, since the correction of deformity places the implants under huge mechanical
stress.[3 ]
[11 ]
[29 ]
[31 ]
[34 ]
[38 ]
[39 ]
[40 ] There are other strategies to improve the construct biomechanical stability and
bone fusion to prevent rod breakage.
A large gap remains between the upper and lower transverse vertebral processes after
PSO. Thus, autologous bone grafting should completely fill the posterolateral sites
bilaterally. Furthermore, interbody implants with autografts in the cranial and caudal
intervertebral disc spaces can be added to improve arthrodesis.[41 ] However, they do not seem to reduce motion or strain; instead they act mainly to
maintain disk height.[42 ]
[43 ] They should preferably be placed prior to the osteotomy, before possible major bleedings.
Although the use of cross-links might stiffen the construct, it can diminish the surface
for bone fusion. One should set the bone graft before placing the cross-links to diminish
this effect.
Placing additional accessory rods, connected to the holding rods with domino/cross-links,
has proved to enhance the stability and stiffness of the construct in cases of 3-column
osteotomy in both biomechanical and clinical studies (17% versus 3% when compared
with standard 2-rod constructs).[11 ]
[44 ]
A biomechanical study[45 ] has shown that regarding the range of motion, two or four rods, made either of titatinum
(Ti) or cobalt chrome (CoCr), have significantly and similarly (94.9% versus 99.4%)
reduced flexion-extension and lateral bending when compared with the intact cadaveric
lumbar spine model. However, total rod strain, which represents the stress delivered
to the rods during the biomechanical cycles, both in flexion and extension, significantly
decreased with accessory rods when compared with the Ti 2-rod (46% versus 65% for
the Ti 4-rod and CoCr 4-rod respectively). Even though the CoCr rod significantly
reduces rod strain, the use of accessory rods with either material provided the most
immediate fixation. Besides, these rods receive greater strain than the primary rods.[45 ]
Deformity corrections with PSO are demanding procedures with high rates of complications
(37% and 67% when performed in the lumbar and thoracic regions respectively), including
12 to 30% of sensitive or motor neurological deficits, most of them transient.[46 ]
[47 ]
[48 ] Intraoperative neurophysiological monitoring has presumably positive effects in
identifying neurological deficits, but it still might neglect some neurological injuries.[49 ] Therefore, although IONM should be used in deformity corrective surgery involving
PSO whenever available, its role in the decrease of new neurological deficits is still
unclear.[50 ] An experimental study in swine[51 ] has demonstrated that spinal cord injury (SCI) occurred when the shortening was
equivalent to the height of one vertebra at the thoracolumbar level. Thus, a PSO performed
to correct sagittal TL hyperkyphosis should not result in neurological damage if judicious
care is taken with dural sac retraction (more protection than retraction) and wide
emerging root decompressions followed by inspection of neural elements during and
after osteotomy closure.
The mean blood loss during a PSO is of 55% of the patient's volemia, and in 24% of
cases there can be losses of ∼ 4 L of blood.[48 ] Thus, a cell saver should be preferably used to avoid massive transfusion. Dural
tear is the most common complication after PSO for the treatment of short-angle kyphosis
(15.8%).[34 ]
Conclusions
The present report highlights the rationale, surgical steps and outcome of spinal
stabilization with the four-rod technique after a PSO in the TL junction. During a
two-year follow-up, there was no pseudarthrosis or implant failure, and the patient
experienced sustained improvement in pain control and quality of life, as depicted
by the self-reported questionnaires. This technique has been proven to increase construct
stiffness and prevent rod breakages in the lumbar spine. Also, the placement of short
rods (and screws) is feasible, and should not considerably increase the complications
and the operating time. Despite this, the technique must still be compared in larger
series to other procedures used in the correction of short-angle kyphosis in the TL
junction, such as circumferential stabilization, as well as PSO and two-rod fixation.