Abstract
Background: Intermediate-term radiographic studies have shown that
anterior and circumferential techniques result in high fusion rates in
patients with high-grade spondylolisthesis, whereas posterolateral fusion is
less successful. We are not aware of any long-term comparative studies in
which these three methods have been evaluated with regard to functional
outcome, including systematic spinal mobility and trunk strength
measurements.
Methods: Sixty-nine of eighty-three consecutive patients with
high-grade isthmic spondylolisthesis who underwent posterolateral
(twenty-one), anterior (twenty-three), or circumferential (twenty-five)
uninstrumented spondylodesis between 1977 and 1991 participated in the study.
The average duration of follow-up was 17.2 years. Radiographs that were made
preoperatively and at the time of the most recent follow-up were assessed with
regard to fusion quality and degenerative changes. Outcome was assessed at the
time of the most recent follow-up by independent observers on the basis of a
physical examination, spinal mobility and nondynamometric trunk strength
measurements, and Oswestry Disability Index scores.
Results: The mean preoperative vertebral slip was 61% in the
posterolateral fusion group, 63% in the anterior fusion group, and 71% in the
circumferential fusion group. The final fusion rate was 86% (eighteen of
twenty-one) in the posterolateral fusion group, 100% (twenty-three of
twenty-three) in the anterior fusion group, and 96% (twenty-four of
twenty-five) in the circumferential fusion group. A decrease in lumbar
intervertebral disc height at the first mobile level superior to the fusion
was noted in five patients in the posterolateral fusion group, seven patients
in the anterior fusion group, and one patient in the circumferential fusion
group (p = 0.037). The mean Oswestry Disability Index score was 9.7 for the
posterolateral fusion group, 8.9 for the anterior fusion group, and 3.0 for
the circumferential fusion group (p = 0.035). Nondynamometric trunk strength
measurements corresponded with referential values. Abnormally low lumbar
flexion affected the posterolateral and circumferential fusion groups more
often than the anterior fusion group (p = 0.0015). The percentage of slip
showed inverse correlations with lumbar flexion, lumbar extension, and trunk
side-bending.
Conclusions: As assessed on the basis of patient-based outcomes,
circumferential in situ fusion provided slightly better long-term results than
did posterolateral or anterior in situ fusion. When the radiographic and
functional results were combined with the patient-based outcomes, the overall
differences between the three groups were small.
Level of Evidence: Therapeutic Level III. See
Instructions to Authors for a complete description of levels of evidence.
Opinions differ with regard to the best method for the surgical treatment
of high-grade spondylolisthesis. Anterior or circumferential spondylodesis is
most often recommended because of the concern that posterolateral in situ
fusion does not always stop progression of the
slip1-5
or the increase in lumbosacral
kyphosis1.
Previous short-term and intermediate-term clinical and radiographic studies
have demonstrated good subjective results and have shown a high fusion rate
after anterior fusion, with or without posterior
fusion4-11.
However, radiographic fusion does not always correlate with clinical and
functional outcome and patient
satisfaction12. In
addition, there have been few long-term clinical, radiographic, and functional
studies comparing posterolateral, anterior, and anteroposterior
(circumferential) procedures, so it has been unclear whether or not more
extensive anterior or circumferential fusion procedures are associated with a
better long-term overall outcome.
The purpose of the present study was to evaluate whether circumferential
fusion is associated with the best long-term clinical, radiographic, and
functional outcome for young patients (defined as patients less than twenty
years old) with high-grade isthmic spondylolisthesis (as indicated by a slip
of >50%) and to compare the functional outcome for these patients with the
findings in the general population. The hypothesis was that circumferential
fusion would be associated with higher fusion rates, which then would be
reflected in more favorable subjective, clinical, and functional outcome
measurements.
Patients
A total of eighty-three consecutive patients who were managed surgically at
our hospital for the treatment of high-grade isthmic spondylolisthesis between
1977 and 1991 were asked to participate in the present study. One patient had
died and, of the remaining eighty-two patients, sixty-nine (84%) agreed to
participate. The reasons not to participate were traveling distances (nine
patients) and lack of interest (four patients). Posterolateral fusion was
performed for twenty-one patients (30%), anterior fusion was performed for
twenty-three (33%), and combined anterior and posterolateral (circumferential)
fusion was performed for twenty-five (36%)
(Table I). The groups were
comparable with regard to the age at the time of the operation
(Table I), but the duration of
follow-up in the posterolateral fusion group was longer than those in the
other two groups. The average duration of follow-up for the entire study group
was 17.2 years.
Methods
Preoperative and postoperative data were collected from the patients'
records. Physical examinations were conducted by three independent observers
(T.L., V.R., and I.H.). Standing anteroposterior and lateral radiographs of
the lumbar spine were made preoperatively and at the time of the most recent
follow-up visit. In addition, flexion and extension lateral lumbar spine
radiographs were made at the time of the most recent follow-up visit. The
Oswestry Disability Index
questionnaire13 was
mailed to the patients along with the invitation to participate in the study.
Besides the Oswestry Disability Index, patient-based outcome was measured with
use of a visual analog scale for back pain, with values ranging from 0 (no
pain) to 100 (maximum pain). Previously validated spinal mobility and
nondynamometric trunk performance tests were performed at the time of the most
recent follow-up
visit14,15.
Operative Technique and Postoperative Treatment
All patients underwent operative treatment because of back pain and a
high-grade spondylolisthesis (defined as a slip of >50%) at L5-S1. Besides
the low-back pain and severe spondylolisthesis, neurological symptoms that
affected daily activities and that were not responsive to conservative
treatment were noted preoperatively, including back pain radiating distal to
the knee without neurological deficiencies (five patients) and neurological
deficiencies or hamstring tightness causing symptoms (fourteen patients).
The posterolateral fusion group comprised twenty-one patients (30%) who had
a standard uninstrumented posterolateral fusion with use of autogenous iliac
crest bone graft. The fusion was from L4 to S1 in seventeen patients and from
L5 to S1 in four patients.
The anterior fusion group comprised twenty-three patients (33%) who had an
anterior in situ fusion with autogenous iliac crest bone graft. The fusion was
performed through a transperitoneal approach with use of one to three
autogenous tricortical iliac crest bone grafts. The fusion was from L5 to S1
in all patients. If necessary, the anteroinferior edge of L5 was resected to
obtain better access to the presacral intervertebral disc space. No attempt
was made to reduce the slipped vertebra, but some reduction could occur as a
result of the lordotic position of the patient on the operating table and the
wedged shape of the interbody bone grafts.
The circumferential fusion group comprised twenty-five patients (36%) who
underwent combined anterior and posterolateral fusion. The anterior L5-S1
fusion was performed as described above. The posterolateral fusion was between
L4 and S1 in thirteen (52%) of the twenty-five patients and between L5 and S1
in twelve (48%). In sixteen (64%) of the twenty-five patients both operations
were performed during a single operative session, and in nine patients (36%)
the operations were performed separately two to three weeks apart.
No spinal instrumentation was used, and no decompression was performed in
any of the patients at the time of the primary fusion procedure. The patients
were mobilized on the second or third postoperative day and wore a soft brace
(posterolateral fusion group) or plastic brace (anterior fusion and
circumferential fusion groups) for four months. No prophylactic antibiotics
were administered.
Physical Examination
All patients underwent a thorough physical examination at the time of the
most recent follow-up visit. In addition to providing demographic data, all
patients reported on any low back pain. Height (in centimeters) and weight (in
kilograms) were measured, and the body mass index (weight [kg]/height
[m2]) was calculated. The finger-to-floor distance was measured in
centimeters. The straight leg-raising test was performed with the patient
supine; the result was considered to be negative when the leg was raised
>60° without causing any back pain or pain radiating distal to the
knee. Patellar and ankle deep tendon reflexes were tested and were classified
as present or absent. Muscle strength for extension of the great toe as well
as for dorsiflexion and plantar flexion of the ankle was tested and was
classified as normal, decreased, or absent. Similarly, sensation in the
dermatomes of L3 through S1 was tested and was classified as normal,
decreased, or absent.
Oswestry Disability Questionnaire
Subjective disability was estimated with use of the Oswestry Disability
Index, with scores ranging from 0 to 100. According to the system of Fairbank
et al.13, low back
disability was classified on the basis of this index as minimal (0 to 19),
moderate (20 to 39), severe (40 to 59), or crippling (=60).
Patients were asked to separately evaluate low back pain and pain radiating
to the lower extremities with use of a visual analog scale, with 0 mm
representing no pain and 100 mm representing maximum pain.
The questionnaire was mailed to all patients before their follow-up visit.
It was completed at home and was returned at the time of the follow-up visit.
The answers were substantiated by the patient during the follow-up visit.
Radiographic Measurements
The magnitude of the L5 slip on S1 was measured on the basis of standing
lateral radiographs and was calculated according to the method of Laurent and
Einola16 as the
quotient of sagittal displacement and the sagittal length of the slipped
vertebral body, expressed as a percentage. Lumbosacral kyphosis was measured
between the posterior aspect of the first sacral vertebral body and the
anterior wall of the body of L5. Lumbar lordosis was measured according to the
system of Wiltse and
Winter17 as the
angle between the planes of the cranial end plates of L1 and L5. Disc height
superior to the fusion level or levels was assessed semiquantitatively on the
basis of lateral radiographs, with the aid of the four-step grading system
recommended by Andersson et
al.18 and Saraste
et al.19, as 0
(normal), 1 (disc height reduced by <50%), 2 (disc height reduced by
=50%), and 3 (disc space completely obliterated). Segmental motion was
measured on the basis of extension and flexion lateral lumbar spine
radiographs that were made at the time of the most recent follow-up visit.
Segmental movement of >3° at any fusion level was defined as a
nonunion. An independent observer (T.L.) measured all radiographs. The
reliability of these radiographic measurements (interobserver and
intraobserver variability) in patients with spondylolisthesis was reported
previously by us20.
For slip percentage, our mean interobserver and intraobserver variabilities
(and standard deviations) were 0.4% ± 0.7% and 0.3% ± 0.8%,
respectively, and for other variables the results were equally good.
Progression of the slip during the follow-up period was regarded as
postoperative "settling" and not a fusion failure if segmental
movement was not seen on the flexion-extension radiographs.
Spinal Mobility and Nondynamometric Trunk Performance Tests
Functional tests, including spinal mobility and trunk muscle strength
measurements, were carried out by the same physiotherapist. Spinal mobility
was determined by measuring lumbar flexion and extension in degrees with a
goniometer. Trunk side-bending was measured with a tape measure from the
fingertips on the thigh to the floor in
centimeters14.
Individual spinal mobility measurements were graded as abnormal when the
values were two standard deviations below the mean of the age and
gender-matched reference values from Finland as previously reported by
Alaranta et al.14.
Nondynamometric trunk strength was evaluated on the basis of repetitive
sit-up, arch-up, and squatting
tests15. The trunk
strength results were scored from 1 (poor) to 5 (excellent). The result was
considered to be poor when it was one standard deviation or more below the
mean of the reference value and was considered to be excellent when it
exceeded the mean by more than one standard deviation.
Statistics
Results are given as the mean and the standard deviation or range.
Statistical comparisons were performed with use of the Kruskal-Wallis test or
the chi-square test, and subgroup comparisons were performed with the Dunn
multiple-comparison test. Correlations were calculated with use of the
Spearman rank correlation test. The level of significance was set at p =
0.05.
Ethical Considerations
All patients provided written informed consent and were aware of the
purpose of the study. We obtained permission to perform this study from the
Ethics Committee of the hospital district where the study was conducted.
Physical Examinations and Oswestry Disability Index
The mean body mass index at the time of the most recent follow-up was 25.7
kg/m2 in the posterolateral fusion group, 23.8 kg/m2 in
the anterior fusion group, and 26.3 kg/m2 in the circumferential
fusion group; these differences were not significant. The mean distances from
the fingertips to the floor with forward bending were 3.9, 1.3, and 5.0 cm,
respectively. Neurological deficiencies that had not been present
preoperatively were noted in some patients at the time of the most recent
follow-up examination. In the posterolateral fusion group, two patients had
unilateral sensory deficiencies in the S1 dermatome. In the anterior fusion
group, two patients had single-dermatome (L4 and L5) sensory loss and one
patient had unilateral total peroneal nerve paralysis postoperatively. Three
patients in the posterolateral fusion group, two patients in the anterior
fusion group, and nine patients in the circumferential fusion group had weak
or no unilateral or bilateral patellar or ankle deep tendon reflexes.
The mean Oswestry Disability Index score was 3.0 (range, 0 to 16) for the
circumferential fusion group, 8.9 (range, 0 to 32) for the anterior fusion
group, and 9.7 (range, 0 to 62) for the posterolateral fusion group. The
difference between the circumferential and posterolateral fusion groups was
significant (p = 0.035 for the comparison of all three groups, Kruskal-Wallis
test; p = 0.045 for the comparison of the circumferential and posterolateral
fusion groups, Dunn multiple-comparison test; and p = 0.051 for the comparison
of the circumferential and anterior fusion groups, Dunn multiple-comparison
test). The Oswestry Disability Index revealed moderate disability or worse (as
indicated by an index score of 20) in three patients (14%) in the
posterolateral fusion group and in four patients (17%) in the anterior fusion
group but in no patient in the circumferential fusion group.
The mean visual analog score for low back pain was 22.6 (range, 0 to 100)
in the posterolateral fusion group, 24.5 (range, 0 to 84) in the anterior
fusion group, and 5.2 (range, 0 to 27) in the circumferential fusion group.
The difference between the circumferential and anterior fusion groups was
significant (p = 0.041 for the comparison of all three groups, Kruskal-Wallis
test; p = 0.082 for the comparison of the posterolateral and circumferential
fusion groups, Dunn multiple comparison test; and p = 0.041 for the comparison
of the anterior and circumferential fusion groups, Dunn multiple-comparison
test).
Radiographic Measurements
Radiographic evidence of nonunion following the primary operation was found
in three patients in the posterolateral fusion group and one patient in the
circumferential fusion group. The fusion rate at the time of the most recent
follow-up was 86% (eighteen of twenty-one) in the posterolateral fusion group,
100% (twenty-three of twenty-three) in the anterior fusion group, and 96%
(twenty-four of twenty-five) in the circumferential fusion group. Progression
of lumbosacral kyphosis of =10° was noted in nine patients in the
posterolateral fusion group, three patients in the anterior fusion group, and
three patients in the circumferential fusion group (p = 0.017). The mean
vertebral slip, the number of patients with a progressive slip, the number of
patients with a decrease in lumbar intervertebral disc height superior to the
fusion level, and the extent of lumbar lordosis are presented in
Table II. Neither the mean
lumbosacral kyphosis nor the mean lumbar lordosis changed significantly in any
group during the follow-up period (Table
II).
Slip progression of 10% at the time of the most recent follow-up visit was
noted in four patients (19%) in the posterolateral fusion group, one patient
(4%) in the anterior fusion group, and three patients (12%) in the
circumferential fusion group; the differences were not significant (p =
0.31).
We separately analyzed the radiographic results and demographic data for
the patients who had either pseudarthrosis or marked progression of the slip
and found no difference between those patients and other patients with respect
to height or body mass index. Similarly, the degree of vertebral slip, the
angle of lumbosacral kyphosis, and the inclination of the sacrum did not
differ between these patients and other patients.
A decrease in lumbar intervertebral disc height at the first mobile level
superior to the fusion was noted in five patients (24%) in the posterolateral
fusion group, seven patients (30%) in the anterior fusion group, and one
patient (4%) in the circumferential fusion group (p = 0.037).
Spinal Mobility and Nondynamometric Trunk Performance Tests
The results of the trunk strength and spinal mobility measurements are
listed in Table III. The range
of lumbar flexion was abnormally low in seventeen patients (81%) in the
posterolateral fusion group, eight patients (35%) in the anterior fusion
group, and twenty-one patients (84%) in the circumferential fusion group (p =
0.0015). Other mobility variables were similar in the three study groups. With
the numbers available, there were no significant differences in sit-up,
arch-up, or squatting scores between the three groups. The percentage slip
correlated significantly inversely with lumbar flexion (rs = 0.56
[95% confidence interval, —0.71 to 0.36]; p < 0.0001), lumbar
extension (rs = —0.29 [95% confidence interval, —0.50
to —0.05]; p = 0.020), and trunk side-bending (rs =
—0.26 [95% confidence interval, —0.48 to —0.01]; p = 0.040).
Lumbosacral kyphosis showed an inverse correlation with the sit-up score
(rs = —0.26 [95% confidence interval, —0.48 to
—0.01]; p = 0.039). Lumbar lordosis did not correlate with either trunk
strength or spinal mobility measurements. With the numbers available, no
correlations were observed between radiographic parameters and the Oswestry
Disability Index or between the Oswestry Disability Index and trunk strength
or spinal mobility measurements.
Complications
Data on complications and reoperations are shown in a table in the
Appendix. A total of one patient (5%) in the posterolateral fusion group, four
patients (17%) in the anterior fusion group, and one patient (4%) in the
circumferential fusion group underwent revision surgery during the follow-up
period. Three patients (14%) in the posterolateral fusion group and one
patient (4%) in the circumferential fusion group had a nonunion. One patient
in the posterolateral fusion group underwent a reoperation for the treatment
of a nonunion, but the remaining three patients with a nonunion were
asymptomatic at the time of the most recent follow-up evaluation and did not
have a reoperation. In one patient in the anterior fusion group, the slip
progressed to a spondyloptosis. Posterolateral fusion was performed two years
after the initial operation, and the patient was asymptomatic at the time of
the most recent follow-up. One patient with a postoperative wound infection
required prolonged hospitalization, but the wound healed with antibiotic
treatment.
Posterolateral in situ spinal fusion is generally accepted as the gold
standard for the treatment of mild
spondylolisthesis21-23.
In cases of high-grade spondylolisthesis, however, posterolateral fusion has
been associated with inferior fusion rates, and anterior or circumferential
fusion has therefore been recommended for these
patients2-5.
The published results of both anterior and circumferential fusion have been
good. However, the clinical outcome tools have not been sufficiently sensitive
or the follow-up times have not been sufficiently long to permit definitive
conclusions to be drawn regarding overall long-term
outcome7,9-11.
Furthermore, we are not aware of any previously published studies that have
compared long-term clinical, radiographic, and functional outcomes after
posterolateral, anterior, and circumferential spondylodesis in patients with
high-grade spondylolisthesis (characterized by a slip of >50%). In the
present study, circumferential spondylodesis resulted in a slightly better
overall outcome than did either anterior or posterolateral spondylodesis when
used for the treatment of childhood or adolescent high-grade
spondylolisthesis.
Various questionnaires and clinical outcome tools have been used to measure
patient satisfaction after spinal fusion.
Seitsalo1 employed
four pain-based outcome categories, Thomsen et
al.22 and Moller
and Hedlund24 used
visual analog scale-based questionnaires, and Gehrchen et
al.25 used a
questionnaire that included items on medication, vocational status, and pain.
We applied the Oswestry Disability Index as a patient-based outcome tool in
our retrospective study. A good patient-based outcome (as indicated by an
Oswestry Disability Index score of <20) was recorded for >80% of
patients, irrespective of the operative method. In terms of the Oswestry
Disability Index scores and back pain visual analog scores, however, we noted
a tendency toward a better patient-based outcome after circumferential fusion.
The good subjective outcome results after anterior or circumferential fusion
are similar to those reported
earlier4,10-11.
The overall outcome after posterolateral fusion was not quite as good as those
after anterior and circumferential fusion. The Oswestry Disability Index
score, in contrast, was worse in the posterolateral fusion group than in the
circumferential fusion group but, unexpectedly, it was similar in the
posterolateral and anterior groups. The amount of vertebral slip or
lumbosacral kyphosis preoperatively or postoperatively did not correlate with
the Oswestry Disability Index score either in the series discussed here or in
patients with low-grade spondylolisthesis in the report by Lamberg et
al.26. Previously,
it was suggested that patients with pseudarthrosis or those undergoing a
repeat arthrodesis have a poorer clinical
outcome9. However,
as there were only four patients with pseudarthroses in our series, this issue
remains unresolved.
In the present study, there was only one fusion failure among the
forty-eight patients in the anterior and circumferential fusion groups,
compared with three fusion failures among the twenty-one patients in the
posterolateral fusion group. Our overall fusion rate is comparable with rates
that have been reported
recently5,7,10-12,
providing further evidence that a high fusion rate can be obtained with both
the anterior method and the circumferential method without instrumentation. In
most of our patients, all fusion methods effectively prevented further
anterior slip of the high-grade spondylolisthesis during the fifteen-year
follow-up period.
A weakness of our study lay in the selection of the operative method. The
preferred method in the late 1970s and early 1980s was posterolateral fusion
as there was a tendency in our hospital to avoid anterior surgery. Later, the
surgeon's preference appears largely to have dictated whether anterior or
circumferential fusion was used. As a result, circumferential fusion may have
been employed in the most challenging cases in an effort to secure a stable
fusion. That this was the case is suggested by the more severe amount of
preoperative slip seen in the circumferential fusion group.
A major concern after spinal fusion has been the fate of the intervertebral
disc superior to the fusion level, although the correlation between
radiographic disc degeneration and clinical symptoms is not
clear11,26,27.
In the present study, radiographs demonstrated an increase in degenerative
changes in the lumbar intervertebral discs in nine patients (43%) in the
posterolateral fusion group, seven patients (30%) in the anterior fusion
group, and one patient (4%) in the circumferential fusion group. However,
these degenerative changes were not reflected in subjective patient
satisfaction as assessed with Oswestry Disability Index scores. The higher
prevalence of degenerative changes after anterior fusion is probably partly
explained by the fact that the first mobile intervertebral disc space was at
L4-L5 in all of the patients in that group, as compared with fewer than half
of the patients in the circumferential and posterolateral fusion groups; in
the remainder of the patients, the first mobile intervertebral disc space was
L3-L4, which is known to be less prone to degenerative changes.
We are not aware of any previous studies on the long-term results of
systematic spinal mobility and trunk strength measurements after fusion in
patients with high-grade spondylolisthesis as compared with those in the
reference population. The values for sit-up and arch-up tests tended to be
higher in the circumferential fusion group than in the posterolateral and
anterior fusion groups. However, irrespective of the fusion method, the
results of trunk strength measurements were, on the average, similar to those
in the healthy reference population discussed earlier by Alaranta et
al.14,15.
Abnormally low lumbar flexion was common in the posterolateral and
circumferential fusion groups. The percentage slip showed inverse correlations
with lumbar flexion, lumbar extension, and trunk side-bending. In addition, an
inverse correlation existed between the sit-up score and lumbosacral kyphosis.
A possible explanation for this finding is that increasing lumbosacral
kyphosis adversely affects the biomechanics of the lumbar spine and makes
sitting up more difficult. The difference in lumbar flexion between the groups
may also be partly attributed to the length of the fusion.
In conclusion, circumferential in situ fusion appears to provide the best
subjective long-term results in young patients under the age of twenty years.
However, the results after posterolateral and anterior fusions were only
slightly inferior. Both functional and radiographic outcomes as well as the
complication rates were similar in all groups, irrespective of the fusion
method used.
A table showing the complications that occurred in this series is available
with the electronic versions of this article, on our web site at
(go to
the article citation and click on "Supplementary Material") and on
our quarterly CD-ROM (call our subscription department, at 781-449-9780, to
order the CD-ROM). ?
Note: The authors thank Timo Yrjönen, MD, Kalevi
Österman, MD, and Pekka Tervahartiala, MD, for their help in conducting
physical examinations of the patients and for giving valuable comments during
the manuscript writing and editing process.
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