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ORIGINAL ARTICLE
Transdiscal L5-S1 screws for the treatment of adult
spondylolisthesis
C. A. Logroscino •F. C. Tamburrelli •
L. Scaramuzzo •G. R. Schiro
`•S. Sessa •
L. Proietti
Received: 15 February 2012 / Accepted: 19 February 2012 / Published online: 9 March 2012
ÓSpringer-Verlag 2012
Abstract
Purpose The aim of the study was to evaluate clinical and
radiographic outcome of patients treated with a modified Grob
technique analysing the advantages related to increased
mechanical stability.
Methods 30 patients that underwent ‘‘in situ’’ fusion for
L5-S1 spondylolisthesis were evaluated. All patients pre-
sented a low-dysplastic developmental L5-S1 spondylo-
listhesis. Patients were divided into two groups: A, in
which L5-S1 pedicle instrumentation associated with
transsacral screw fixation was performed, and B, in which
L5-S1 pedicle instrumentation associated with a postero-
lateral interbody fusion (PLIF) was performed.
Results Patients treated with transdiscal L5-S1 fixation
observed a faster resolution of the symptoms and a more
rapid return to daily activities, especially at 3–6 months’
follow-up. The technique is reliable in giving an optimal
mechanical stability to obtain a solid fusion.
Conclusions The advantages of this technique are lower
incidence of neurologic complications, speed of execution
and faster return to normal life.
Keywords Spondylolisthesis Surgical technique
Fusion Back pain Radicular pain
Introduction
The optimal treatment of high-grade spondylolisthesis is a
controversial issue. It is well known that symptomatic
high-grade slip, resistant to conservative management
requires surgical stabilization [1,2]. Good results may be
obtained in low-dysplastic spondylolisthesis with ‘‘in situ’’
fusion [3]. In this type of spondylolisthesis a reduction is
generally unnecessary to obtain good biomechanical and
neurologic recovery. In situ fusion is a relatively safe and
reliable procedure associated with a high rate of arthrodesis
and at lower risk of neurologic injury [4,5]. The main
argument against reduction manoeuvers in spondylolis-
thesis is the high incidence of neurologic complications, as
high as 31% [6]. Different surgical procedures could be
used to obtain ‘‘in situ’’ spondylodesis: posterolateral
fusion with or without instrumentation, posterior interbody
fusion, combined anterior and posterior procedures and
circumferential 360°fusion. Circumferential fusion as
showed by Lamberg et al. [7], had better long-term results
than isolated posterolateral fusion or anterior fusion alone.
A few posterior surgical techniques could be used to
achieve circumferential stabilization, including transverte-
bral pedicle screw fixation [8], posterior transsacral inter-
body fusion using a cortical bone graft with pedicle screw
implantation [1], posterior interbody cage and pedicle
screw fixation [9] and a posterior pediculo-body fixation
alone or associated with fusion at the superior level to
obtain a greater mechanical stability [10]. The last one
technique combines the possibility of a three-column sta-
bilization with the simplicity and speed of fixation; but
presents limited indications: a significant reduction in the
height of the interposed disc, a vertebral slippage of at least
25% and a good balance of the spine in the sagittal plane.
The aim of the study was to illustrate our modifications
to Grob technique and to analyse the 5-year results
obtained with this modified technique into surgical treat-
ment of low-dysplastic L5-S1 spondylolisthesis compared
with traditional posterior lumbar interboby fusion.
C. A. Logroscino F. C. Tamburrelli L. Scaramuzzo
G. R. Schiro
`S. Sessa L. Proietti (&)
Department of Orthopedic Science and Traumatology
Spine Surgery Division, Catholic University Rome,
Largo A. Gemelli 1, 00168 Rome, Italy
e-mail: proiettil@yahoo.it
123
Eur Spine J (2012) 21 (Suppl 1):S128–S133
DOI 10.1007/s00586-012-2229-8
Methods
From January 2005 to September 2010, 30 patients
underwent ‘‘in situ’’ fusion for L5-S1 spondylolisthesis. All
patients presented a low-dysplastic developmental L5-S1
spondylolisthesis characterized from low back pain and leg
pain and had a failed trial of conservative management. In
all patients a pre-operative radiographic analysis with full
length, plain, dynamic X-rays of the spine was performed.
Spinopelvic parameters as pelvic tilt, sacral slope and
pelvic incidence were analysed with dedicated software
(Kodak DirectView Picture Archiving and Communication
System). Severity index was also calculated following La
Martina criteria [11]. A horizontal line was drawn through
the centre of S2 on a standing lateral radiograph of the
lumbar spine that includes the hips. A vertical line is drawn
through the centre of the femoral heads. A second, vertical
line is drawn through the middle of L5 inferior end plate.
The distance from the centre of S2 to the vertical of the
centre of the femoral heads is D2; the distance from the
vertical of the middle of L5 inferior end plate to the vertical
of the centre of the femoral heads is D1. The SI is calcu-
lated as follows: SI =D1 9100/D2. A neuroradiological
analysis with an MRI of the lumbar spine was also per-
formed to evaluate neurological structures and L5-S1 disc
degeneration according to Pfirrmann criteria [12]. Inclusion
criteria were low back and radicular pain resistant to medical
and physical treatment, a low-dysplastic developmental L5-
S1 spondylolisthesis with severity index B20%, a L5 vertebral
slip[25%, a Pfirrmann grade between IV b and V. Patients
were divided in two groups: group A (15 patients) in which
L5-S1 pedicle instrumentation associated with transsacral
screw fixation was performed and group B (15 patients) in
which a L5-S1 pedicle instrumentation associated with a
posterolateral interbody fusion (PLIF) was performed. In both
groups a full decompression and a posterolateral fusion were
performed. For each group, we analyzed surgical time, intra-
operative blood loss, perioperative complications and radio-
graphical parameters. Pain was evaluated with the Visual
Analogue Scale (VAS) preoperatively at 1 month, 3, 6 and
12 months and annuallypostoperatively. The ‘‘Short-Form 36
General Health Survey’’ was assessed preoperatively at
1 month, 3 months, 6 months, 12 months and annually after
surgery. Standard X rays were performed at 30 days, 3, 6 and
12 months and annually postoperatively. All data were
recorded and statistically analysed in a retrospective way.
Statistics
Descriptive statistics were calculated. The results obtained
were analysed using the student’s t Test and v
2
Test and
verified with Fisher’s exact test. Significance was accepted
at p\0.05. There are some limitations that need to be
acknowledged and addressed regarding the present study.
The number of cases is too limited for broad generaliza-
tions. Further empirical evaluations and greater patients’
series are needed to validate the present results.
Surgical technique
Group A
All patients were placed in a prone position on a carbon
fibre operating table to have an optimal fluoroscopic
visualization of the involved spine in the antero-posterior
and lateral views. A lumbosacral longitudinal incision was
made and a bilaterally subperiosteal dissection of the par-
avertebral muscles was performed to expose the affected
level. Extensive decompression was performed and the
affected nerve root decompressed adequately. The entry
point of transdiscal screw was near S2 nerve root on the
body of S1 and was identified 1 cm distally and 1 cm
medially with respect to the standard S1 pedicle screw
entry point. The drill was passed under fluoroscopic guid-
ance into the S1 vertebral body, than traversing through
L5-S1 disc space, and then into the L5 vertebral body. An
AO 6.5 cancellous bone screw of appropriate length
(Synthes Raynham, MA, USA) was implanted. (Fig. 1).
The same procedure was repeated on the other side to
stabilize the slip between L5 and S1. This posterior
transdiscal L5-S1 fixation was implemented with pedicle
screw instrumentation at L5 and S1 (EXPEDIUM SYS-
TEM, DePuy Spine, Raynham, MA, USA) and with a
posterolateral fusion with autologous iliac crest bone graft,
obtaining ‘‘in situ’’ fusion (Figs. 2.1, 2.2, 2.3, 3.1, 3.2).
Group B
The same standard posterior approach described for the
group A was used. Under fluoroscopic control four pedicle
screws were inserted in L5 and S1 (EXPEDIUM SYSTEM,
DePuy Spine, Raynham, MA, USA). Then a posterior L5
bilateral laminectomy and a L5-S1 discectomy were per-
formed. The epiphyseal plates of the involved level were
prepared and two interbody cages (Faber DePuy Spine,
Raynham, MA, USA) filled with autologous bone graft
were introduced using posterolateral approach. The rods
were fixed to the screws in a compressive way. A pos-
terolateral fusion with autologous iliac crest bone graft was
performed in all patients.
Results
There were 17 males (56.6%) and 13 females (44.3%); the
mean age was 52.5 years (range 33–69). All patients were
Eur Spine J (2012) 21 (Suppl 1):S128–S133 S129
123
affected by L5-S1 developmental spondylolisthesis with
lysis in 16 cases and with pars interaricularis elongation in
14 cases. The mean operative time was 135 min (range
75–190) in group A versus 400 min (range 180–375) in
group B. The mean intra-operative blood loss was 290 cc
(range 210–370) in group A versus 520 cc (range 390–980)
in group B. Both groups observed an improvement in
radicular pain; however, in the first group we observed a
faster resolution of the symptoms and a more rapid return
to daily activities, especially at 3–6 months’ follow up. The
mean follow-up was 3 year (min 1–max 5 years). A con-
firmation of this trend could be seen in VAS and SF-36
results with a faster decrease in the obtained values yet to
one month’s follow-up. In the first group the average pre-
operative VAS score was 8.5 (range 7–9.5) decreased to
5(range 3–6) at one month’s follow-up; to 2.5(range 1–3.5)
at 3 months follow-up, to 0.9 (range 0–2) at 6 months’
follow-up; to 0.2 (range 0–0.5) at 12 months minimum
follow-up (p=0.003) (Fig. 4). In group B the average pre-
operative VAS score was 8.5 (range 7–9.5) at base time,
decreased to 3.1 (2.5–4.5) at 1 month’s follow up, a further
decrease was seen at 3-, 6- and 12 months’ follow-up with
a mean value, respectively, of 1.5 (range 1–3); 0.3 (range
0–1); 0.2 (0–0.5) (p=0.004).
The Short-Form 36 Physical Health in the group A was
equal to 35% (range 22–48%), to 64% (range45–52%) at
1 month, of 75.4% (65.3–86.4%) after 3 months, of 82%
(71.4–92.2%) after 6 months and of 92% (83–98%) after
12 months’ minimum follow-up (p\0.001) (Fig. 5). The
Short-Form 36 Physical Health in the group B was equal to
28% (range 23–41%) at base time, to 43% (range 35–55%)
at 1 month, of 60% (range 53–71%) after 3 months, of
75% (range 59–85%) at 6 months and of 85% (69–91%)
(p=0.003) at 12 months’ minimum follow-up (Fig. 6).
The Short-Form 36 Mental Health was in the group A of
38% (range 35–43%) at base time, of 64% (range54–71%)
at 1 month, of 76% (range 71–83%) at 3 months, of 90%
(range 82–94%) at 6 months and of 92% (83–97%) at
12 months’ minimum follow-up, p\0.001 (Fig. 3). The
Short-Form 36 Mental Health SF-36 mental was in the group
B of 35% (range 28–46%) at base time, of 46% (range31–67%)
at 1 month, of 62% (range 48–73%) at 3 months, of 78% (range
66–91%) at 6 months and at 85% (69–91%) at 12 months
minimum follow-up p=0.005 (Fig. 4).
The severity index was in group A 19.2% at base time
unchanged at 1-year medium follow-up, 19.7% at base time in
the group B unchanged at 1-year minimum follow-up.
The pre-operative spinopelvic parameters were
unchanged in both groups at 1-year medium follow-up. In
group A the mean pre-operative SS was 42.2°(range
38–65°) and the mean pre-operative PT was 27.7°(range
16–32°) unchanged at 1-year minimum follow-up. In the
group B the mean pre-operative SS was 46.3°(range
37–68°) and the mean pre-operative PT was 25.9°(range
15–34°unchanged at 1-year minimum follow-up.
We observed one deep wound infection in the group A,
which required revision surgery and one superficial wound
infection in the group B resolved with antibiotic therapy
administration. In group A one S1 pedicle screw mis-
placement was observed in a patients showing radicular leg
pain which required revision surgery. In group B we
observed one transitory L5 neurological deficit resolved
Fig. 1 Schematic view of the screw entry point in the Grob modified technique 1 cm medially and 1 cm inferiorly, the S1 pedicle screw and
correspondent view in anteroposterior X-ray
S130 Eur Spine J (2012) 21 (Suppl 1):S128–S133
123
with physiotherapy. No hardware failure, or slip increase
was observed.
Discussion
The most useful classification system for spondylolisthesis,
which gives also information about prognosis and therapy,
is that of Marchetti and Bartolozzi [13]. In this system,
spondylolisthesis is divided in two major groups, devel-
opmental and acquired. Developmental are divided in two
subgroups: low dysplastic and high dysplastic, including
that with lysis and elongation. The low-dysplastic type is
characterized by normal S1 and L5 vertebral shape, a
normal lumbosacral profile and a balanced pelvis without
retroversion. Because of the absence of bony morphologic
changes and of spinopelvic inbalance this type of spond-
ylolisthesis is at lower risk of slip progression compared
with high-dysplastic [14]. Spinopelvic imbalance can
modify the biomechanical load at the lumbosacral junction
and creates compensatory mechanism to maintain adequate
posture and gait. In clinical practice is difficult to differ-
entiate low-dysplastic from high dysplastic spondylolis-
thesis, especially in young subjects [11]. A first attempt to
differentiate these two pathologies was made by Vidal
and Marnay introducing the Index C (couple-charnie
`re)
[14]. This index was a calculation of the opposing torque
generated by the anterior displacement of the hips conse-
quent to the loosening of the auditory meatus travel, L5-S1
and the centre of femoral head alignment. In 2009
Lamartina et al. [11] gave a numerical value to this torque
introducing the Severity Index (SI) obtained as follows:
SI =D1 9100/D2. The SI became a simple criterion in
the characterization and assessment of slip progression and
in differentiating low from high dysplastic spondylolis-
thesis. As demonstrated by Vidal and Marney [14]aSI
\20% is present in normal subjects and also in low-dys-
plastic spondylolisthesis patients since there was no pelvic
retroversion. A SI [20% and pelvic retroversion charac-
terized the high-dysplastic spondylolisthesis. In this type of
spondylolisthesis reduction is mandatory to restore the
spine physiological alignment, the sagittal balance and to
correct the pelvic retroversion, avoiding non union and slip
progression seen in this group with an ‘‘in situ’’ fusion [15].
Reduction is gravened by a great risk of neurologic com-
plication with an incidence of 31% [6]. In low-dysplastic
Fig. 2 1Standard A-P and LL X ray showing a L5-S1 low dysplastic
developmental spondylolisthesis. 2X ray at maximum flexion and
extension. 3Sagittal view MRI showing a degenerated L5-S1
(Pfirrmann V) intervertebral disc
b
Eur Spine J (2012) 21 (Suppl 1):S128–S133 S131
123
developmental spondylolisthesis reduction is unnecessary
since there is no pelvic retroversion and sagittal unbalance
[11]. ‘‘In situ’’ fusion has reported in this type of spond-
ylolisthesis satisfactory clinical outcomes and good fusion
rate. [11,16]. Different surgical techniques to obtain ‘‘in
situ’’ fusion have been described. Grob et al. [10] suggest a
pediculo-body fixation with two cancellous screws inserted
from the S1 pedicle to the L5 vertebral body. This tech-
nique was also reported by Zagra et al. with satisfactory
long-term outcome [17]. Bartolozzi et al. [9] described an
in situ interbody fusion with a titanium cage inserted
according to the Bohlman and Cook [18] technique by a
transacral approach associated with pedicle screw fixation.
In this study we introduce a modification to Grob technique
obtaining a new ‘‘in situ’’ fusion. The modification was
introduced to obtain a higher mechanical stability using a
six-screw fixation at one level. We modified the entry point
of the trandiscal-transvertebral screw. The entry point of
transdiscal screw has to be identified meticulously 1 cm
medially and 1 cm distally to S1 pedicle screw entry point
to avoid impingement between these screws. The identifi-
cation of the sacral foramen is mandatory to avoid neuro-
logic complications due to transdiscal screw misplacement.
The analysis of our data showed a great reliability of this
Fig. 3 Anteroposterior and lateral view of post-operative L5-S1 low-dysplastic developmental spondylolisthesis X-ray treated with Grob
modified technique
Fig. 4 Visual Analogue Scale score results after a 12-months’
follow-up; patients (n=15) group A and B Fig. 5 Group A results of the SF-36 physical and mental component
after a 12-months’ follow-up; patients (n=15)
S132 Eur Spine J (2012) 21 (Suppl 1):S128–S133
123
surgical technique, a lower operative time, lower intraop-
erative blood loss resulting in better clinical outcome and
faster return to normal day-life compared with traditional
interbody fusion group. At 5-year follow-up we observed
no hardware failure. The complications were not statisti-
cally significant. The success of this technique is due to the
correct indication: a SI\20%, a slip[25% and a Pfirrmann
grade of at least IVB.
Conclusion
The analysis of the 5-year follow-up data of low-dysplastic
developmental spondylolisthesis with this modified tech-
nique gave satisfactory results. The technique is reliable in
giving an optimal mechanical stability to obtain a solid
fusion. The advantages are the lower incidence of neuro-
logic complications, the speed of execution and the faster
return to normal life of treated patients. The limits of the
study are the retrospective analysis and the small number
of cases.
Conflict of interest None.
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