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Hybrid Lumbar Fusion:
A clinical and radiological review at 2 years
*Dyson P., **Abuhadra K.,
*Warren M.
*The Luton and Dunstable Hospital, Luton
Bedfordshire, England
**Orthopedic Section, Surgery Department, Hamad
Medical Corporation, Doha, Qatar
  Abstract:
We report on our first 20 patients treated with
hybrid lower lumbar stabilization, in which one
or more segments were treated with caged
interbody fusion by PLIF technique and one or
more adjacent segments were stabilized using
GRAF instrumentation.
The indications for interbody fusion included
spondylolysis; previous failed disc surgery, and
primary discopathy with positive discography
and/or active modic signal on MRI.
The indication for flexible stabilization of
adjacent segments was for disc degeneration on
MRI scanning with or without evidence of
posterior annular tear.
This was a prospective study with clinical
evaluation using VAS pain scales and Oswestry
disability score. All patients were reviewed by
an independent consultant radiologist to assess
integrity of the implant after two years and
underwent CT scanning to assess progression of
the caged fusion. There were no instances of
failed fusion in this group and no cases of
implant failure.
 Introduction:
The clinical
outcomes of flexible lumbar stabilization using
the GRAF method have been reviewed by Gardner(1,2)
who has reported clinical improvement in 70% of
cases of symptomatic lumbar disc degeneration.
Our own experience has been similar, and has
confirmed certain contra-indications for
flexible stabilization.
1. GRAF
stabilization has never been recommended for
spondylolisthesis.
2. Success rates below 50%
have been reported in revision cases.
3. The result in patients
with Modic changes in the adja- cent end plates
are inferior to those reported with inter- body
fusion.
We therefore recommend interbody fusion rather
than GRAF stabilization where surgery is
undertaken for the above indications.
The assessment of interbody fusion remains
confounded by the fact that clinical outcomes do
not correlate well with successful radiological
fusion. Failed radiological fusion, however,
remains an unsatisfactory outcome for patients
and their surgeons, and it is recognised that
this is increasingly likely to occur according
to the number of levels operated. Agazzi S,
Reverdin A et al report successful fusion in 98%
of cases at one level, 90% at two levels, and
only 70% at three levels(3).
Gardner has reported
excellent outcomes when using the GRAF methods
in symptomatic transitional segments adjacent to
previous successful fusion.
It would therefore
seem logical when there is established disc
degeneration adjacent to an intended fusion to
perform a hybrid procedure in which the
secondary degenerative level is controlled by
flexible stabilization. This procedure has also
been referred to as “Topping Off” and several
manufacturers have produced devices to address
the issue. There have been no reports as yet to
assess the efficacy of such devices.
We have found it
relatively simple to combine the implant we are
currently using for PLIF surgery (Diapason,
Stryker) with the GRAF system. The purpose of
this report is to establish whether such usage
is clinically effective and, in particular,
whether such usage might lead to unpredictable
implant failure.
Patients
and Methods:
This study reports
the outcomes of twenty consecutive patients
operated upon by the senior orthopedic surgeon
(PD) using hybrid stabilization between January
1996 and June 1998. The minimum follow up is
therefore two years (range 2.1 to 4). Patients
were scored prospectively using VAS for back and
leg pain and Oswestry disability score, and
these were repeated at final follow up.
Post-operative
lumbar spine radiographs were independently
reviewed (MW) to ascertain the integrity of the
pedicle screws and to assess the extent of
fusion. Spiral computed topography (SCT) with
sagittal and coronal reconstruction was
performed using a General Electric Hi-Speed
Advantage 3.1. In three patients the slice
thickness was 3 mm with pitch of 1.5 throughout
and in four patients the slice thickness was 3
mm through the pedicle screws and 1 mm with a
pitch of 1.5 through the cages.
Successful
radiological fusion was assessed using a
combination of the plain radiographic and SCT
findings using the following criteria:
1. Presence of high
attenuation material (trabecular bone) in and
between the cages.
2. Presence of high
attenuation material (trabecular bone) anterior
to the cages (sentinel sign).
3. Absence of bone resorption in adjacent end
plates.
Results:
Of the twenty patients reviewed, only fifteen
replied to the questionnaire for the assessment
sent to them, making the response rate 75%, the
female /male ratio is (2:1) chart no 4, There
were no complications in this group in terms of
neurological damage, infection, wound haematoma,
pedicle fracture or implant malposition.
The Oswestry scores were analyzed pre- and
post-operatively using t-Test Paired Two Sample
for Means show that P value 0.001 which is
statistically significance (Table 1).
The VAS score for the leg pain pre and post op
as well as the back pain, using t-Test: Two
Sample Assuming Unequal Variances show the P
value to be 0.002, and 0.00009 which is very
significant statistically (Table 1 and
Table 3).
Of the twenty patients, eleven had radiological
investigations available for review. Plain
radiographs alone were reviewed in four patients
and in these no SCT had been performed. Plain
radiographs and SCT were reviewed in six
patients and SCT alone in one patient.
Plain radiographs in ten patients showed no
evidence of abnormality in the end plates
adjacent to the cages and there were no
complications relating to the pedicle screws. In
two patients, in whom SCT had not been
performed, there was a small amount of bone
density material lying anteriorly within the
intervertebral disc space on respectively the
three month and at thirty-three month
post-operative radiographs. In another patient
the amount of bone density material was
extensive on a two months post-operative
radiograph and was confirmed by SCT at twelve
months after operation.
In the seven patients with SCT for review, there
were eight intervertebral disc spaces for
evaluation containing sixteen cages. All sixteen
of the cages contained high attenuation material
consistent with bone and there was no evidence
of bone resorption or sclerosis in adjacent end
plates. Of the eight intervertebral disc spaces,
four (in four patients) showed high attenuation
material outside the cages and in three of these
the amount of material was small with only one
showing an appreciable amount. The high
attenuation material lay anterior to both cages
and lateral to the right cage in two instances,
anteriorly alone in one and between the cages in
another.
Discussion:
The assessment of fusion by conventional
radiography is problematic not least because it
is often technically difficult to visualize the
lower lumbar intervertebral disc spaces in
profile. Conventional radiography is a
relatively insensitive method of detecting bone
formation within the intervertebral disc space
and SCT is far more sensitive, although it
entails a higher radiation dose. However,
artifacts from both the titanium cages and
pedicle screws hinder SCT interpretation and
make absolute measurement of attenuation values
unreliable.
In this series the surgical technique used
involves the insertion of bone graft material
into both the cages and the intervertebral disc
space. Thus the bony attenuation material
observed on SCT may simply represent
consolidated bone graft and it is not certain if
true new bone formation has occurred. This
uncertainty could only be ascertained by further
SCT after a longer interval.
Although the outcomes of this series appear
favorable there is no evidence at this stage
that they are superior to conventional fusion.
There may be a theoretical advantage with
decreased stress at the transitional zone.
There is no doubt that two and three level
fusion is an arduous procedure and is greatly
simplified by reducing the number of levels
fused. This series suggests that this can be
achieved by using the hybrid technique
described. We have not experienced any fusion
failure using conventional assessment techniques
and there has been no prosthetic failure.
References:
1. Gardner A;
Declerck GM.The GRAF ligamentoplasty procedure,
Spine 2000 Jan15; 25(2): 273-6.
2. Brantigan JW;
Pseudarthrosis rate after allograft PLIF: Spine
1994 Jun 1; 19(11): 1271-9.
3. Agazzi S;
Reverdin A; May D; PLIF with cages: An indepen-
dent review of 71 cases, J Neurosurgeon 1999oct;
91(2 suppl): 186-92.
4. Paul
C.Mcafee; IBF cages in Reconstructive operations
on the spine; JBJS June1999. |
