Postoperative Lumbosacral Instability: Proposal of a New

WSJ. 2007;2(1):16-21
Volume 2: Issue 1
Postoperative Lumbosacral Instability: Proposal of a New
Classification Based on Etiology
Sait Naderi, MD1; Özgür Akşan, MD2; Süleyman Men, MD2; Levent Fırat,
MD3; Tansu Mertol, MD2; M. Nuri Arda, MD2
Yeditepe University School of Medicine, Department of Neurosurgery, Istanbul, Turkey,
Dokuz Eylul University School of Medicine, Department of Neurosurgery, Izmir, Turkey,
3
Dokuz Eylul University School of Medicine, Department of Radiology, Izmir, Turkey
1
2
Abstract
Objective:
Postoperative lumbosacral instability is one of the causes of failed back surgery syndrome. This process
results from a variety of preoperative, intraoperative and postoperative reasons. A careful preoperative
workup and planning can decrease the rate of this type of instability. The aim of this study is to review the
results of surgery for postoperative instability, and to determine the factors contributing to its formation.
Methods:
Between 1998 and 2005, 22 cases of postoperative lumbosacral instability were operated. The charts and
radiographs could be reviewed in 18 cases. The study was designed in two parts. The first part consisted of
the general retrospective review of cases, and the second part consisted of analysis of factors contributing
to formation of instability.
Results:
There were 13 female and five male cases aged from 30 to 74. Instability occured after six months to 19 years
after primary surgery. The diagnosis during the primary surgery was lumbar disc herniation in 14 cases,
lumbar spinal stenosis in two cases and instrumentation of degenerative spondylolisthesis in two cases.
The causes of instability include preoperative overt instability in 11.1%, aggressive bony resection in 61.2%
and adjacent level degeneration in 11.1% of cases. A transpedicle screw fixation and intertransvers fusion
procedure were performed. The Odom Clinical Situation was evaluated as excellent in 77.9%, good in 16.6%
and poor in 5.5% of cases. The second part of the study revealed that postoperative instability was associated with an increased L4-5 facet angle and decreased lumbar lordosis angle.
Conclusion:
It is concluded that aggressive facet resection during the primary surgery was the most important cause
of postoperative lumbosacral instability. Increased facet angle and decreased lumbar lordosis angle were
the main contributing factors. All these factors need to be taken into consideration before and during the
primary lumbosacral surgery.
Key Words:
instability, laminectomy, postoperative, spondylolisthesis
Introduction
Many authors sought to predict the formation of postoperative lumbosacral instability. They studied many factors,
including age, disc height, the presence of abnormal motion
in dynamic radiographs, the amount of bony resection, and
the facet angle.(4, 5,9,10,19-27) However, controversies remain.
The aim of this study is to review the clinical and radiological data in cases operated for postoperative lumbosacral
instability and to determine the factors affecting formation
of instability after surgery.
Lumbosacral instability is one of the causes of failed back
surgery syndrome complicating the postoperative course.
This process results in low back and/or leg pain. A variety
of preoperative, intraoperative and postoperative factors
may lead to postoperative lumbosacral instability.(1-18)
The main preoperative cause of postoperative lumbosacral
instability include failure to notice the preoperative instability or avoiding fixation procedure. The major intraoperative
cause of postoperative lumbosacral instability is aggresive
bony and ligamentous decompression, whereas the major
postoperative reasons include adjacent level degeneration in
already fixated cases and natural degeneration of the lumbosacral spine.
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Postoperative lumbosacral instability
Volume 2: Issue 1
Materials and Methods
Results
Ninety-seven cases with lumbosacral instability underwent
surgery between 1998 and 2005. Twenty two (22.8%) out
of 97 cases were classified as postoperative lumbosacral instability. Three patients were missed during follow up, and
could not be included to the study. The clinical and radiolagical data of 18 cases with postoperative lumbosacral instability were retrospectively reviewed.
The radiological studies included plain AP and lateral
lumbosacral radiography, lateral dynamic (flexion-extension) lumbosacral radiography, lumbosacral magnetic resonance imaging (MRI) and computed tomography (CT). The
indications for surgery included presence of axial pain with
or without leg pain concomitant with radiological signs of
lumbosacral instability, i.e., presence of abnormal motion (>
4mm) and angulation (> 20° for L3-4 and L4-5 and 25° for
L5-S1 level) in flexion and extension radiographs.
The study was designed in two parts. Part I consisted of
the general review of the cases, and part II consisted of the
analysis of the factors affecting instability.
Part I: The retrospective analysis include the age, gender, the number and location of instable segments, the diagnosis of primary surgery, the duration between the primary
surgery and admission for instability, the causes of instability, the type of surgical treatment and surgical outcome using VAS score and Odom Scale.
Part II: To detect the factors affecting occurence of postoperative instability, following radiological parameters were
analysed: Facet angle, lordosis angle, disc height and facet
resection amount. The results obtained from the patient
group were compared with the results of asymptomatic individuals of a control group.
The facet angle was measured as described elswhere.(28)
The mean facet angles of the L3-4, L4-5, and L5-S1 levels
were compared with the facet angles of analoge levels of control group.
The lumbar lordosis angle was described as angle between the lines intersecting the lines parallel to the L1 and
S1 superior endplates. The angle obtained from the patient’s
group was compared with the control group’s mean angle.
The disc height of each level was measured as the mean
of height of anterior and posterior aspect of intervertebral
disc, and the obtained results were compared with results of
the control group.
The amount of facet resection was measured in axial
lumbar spine CT with respect to the contralateral side.
Part II. Factors Affecting to Formation of Iatrogenic Instability
There was no statistically significant difference between the
facet angles of L3-4 and L5-S1 levels of the control group
and patient group. The mean facet angles in L4-5 level of the
patient group was 52º±15.5º in the right, and 41.8º±18.13º
in the left side. When compared with the control group, the
patient group facet angle was statistically larger (p<0.001 in
the right, p<0.05 in the left) (Table 3).
The mean lordosis angles were measured as 20.82º ±
11.08 and 43.53º ± 18.35 in patient and control groups, respectively (p<0.001).
Part I. General Results
There were 13 female and five male cases, aged from 30 to
74 (mean 49.7). There was a one-segment instability in 16
(88.9%), and two-segment instability in two cases (11.1%).
Instable segment was located at L3-4 in two cases (%11.1), at
L4-5 in nine cases (50%), and at L5-S1 level in seven cases
(38.9%).
The instability occured after hemipartial laminectomy
for lumbar disc herniation in 14 (77.8%), after laminectomy
for lumbar spinal stenosis in two (11.1%), and long time after
lumbar instrumentation for degenerative spondylolisthesis
in two cases (11.1%) (Table 1).
The duration between the first primary surgery and admission for instability ranged from 6 months to 19 years.
The radiological investigations revealed that there was
a preoperative instability in two cases (11.1%), whereas instability was secondary to intraoperative reasons (>%50
facetectomy) in 11 cases (61.2%). In two cases (11.1%) who
underwent spine instrumentation 10 years ago, instability
was secondary to adjacent level degeneration after spine
instrumentation. In three cases (16.6%) no reason could be
detected (Table 2).
A one-segment (two vertebrae) pedicle screw fixation
was performed in 14 cases, two-segment fixation in three
cases, and a three-segment fixation was performed in only
one case.
Follow-up ranged between 18 months and 80 months
(mean 50.2). Preoperative VAS was 7.9±1.1, whereas postoperative VAS was 3.1±1.4.
The Odom clinical situation was found to be excellent
in 14 (77.9%) cases, good in three (16.6%) cases, and poor in
one case (5.5%).
Table 1. The diagnosis of primary surgery
Table 2. The causes of iatrogenic instability
Lumbar disc herniation
Lumbar spinal stenosis
Degenerative spondylolisthesis2
Overt preoperative instability
Aggressive bony resection
Adjacent level degeneration after spine instrumentation
No detectable reason
14 (77.8%)
2 (11.1%)
(11.1%)
2 (11.1%)
11 (61.2%)
2 (11.1%)
3 (16.6%)
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Naderi et al
Volume 2: Issue 1
ported that development of postoperative spondylolisthesis
was related to facet joint orientation and dimensions, rather
than the absolute amount of joint removed.(39) In a similar study, Naderi et al reported the importance of increased
facet angle in L4-5 level spondylolisthesis.(28) In a second
study, Naderi et al reported that intraoperative reduction
was achieved easier in cases with increased facet angle. On
the other word, increased facet joint angle both predispose
instability and facilitate reduction of slipped vertebra.(31)
The present study supported the effect of increased
L4-5 facet angle in the occurence of postoperative lumbosacral instability. Based on the aforementioned studies, we
recommend an additional fixation procedure in cases with
increased facet angle who are candidates for aggressive lumbosacral decompression, even if there is no overt instability.
There are controversies regarding the effect of narrowed
intervertebral disc on postoperative instability. A narrowing
of the intervertebral disc more than 30% was reported to be
a clear sign of segmental instability by Schaller et al (16),
whereas Robertson et al addressed the stabilizing effects of
reduced disc height.(29) The current study failed to demonstrate a clear association between the intervertebral disc
height and likelihood of postoperative instability.
Another controversial factor is the angle of the lumbar
lordosis. This study demonstrated a decrease in the lumbar
lordosis in cases with postoperative lumbosacral instability.
The disc height was measured as 8.3 ± 2.4 mm, and
7.9 ± 3.3 mm, in control and patient groups, respectively
(p>0.05).
Discussion
This study revealed that the postoperative instability was
most commonly secondary to aggressive facet resection during lumbar disc herniation surgery. Increased facet angle and
decreased lumbar lordosis angle were the main contributing
factors. All these factors need to be taken into consideration
both before and during the primary lumbosacral surgery.
There are many reports on the occurence of instability
after macro and microdiscectomy procedures, as well as after laminectomy for lumbar spinal stenosis. There is lack of
consensus regarding the factors contributing to formation
of instability. Principally, these factors can be categorised as
preoperative, intraoperative and postoperative factors. Such
a categorization facilitates the understanding of causes of
postoperative lumbosacral instability.
Preoperative Reasons
Preoperative reasons may cause postoperative lumbosacral
instability in two manners; (1) presence of an overt spinal
instability and (2) presence of factors predisposing postoperative instability. Both are of importance and require a
careful preoperative clinical and radiological assessments.
This dictates the use of dynamic radiographs to find out the
abnormal motion and instable segments before lumbosacral
spine surgery.
It is of note that the preoperative study should be focused not only to abnormal motion, but also to other casespecific anatomic variations such as facet joint angle, lumbar lordosis and disc degeneration as evidenced by traction
spurs or diminished disc height, Modic’s signs as well as facet size. The aforementioned factors are important variables
and contribute to the sagittal spinal geometry and preserve
intrinsic spine load bearing abilities.
The contribution of facet joint orientation to instability
was studied by many authors.(28-30) Roberstson et al re-
Intraoperative Reasons
Facet joint, pars interarticularis, lamina, interspinous and
supraspinous ligaments are the main posterior osseoligamentous structures preserving spinal stability. Resections
of posterior bony or ligamentous structures normally lead
to a decrease in stability. The degree of instability depends
on the extent of resection, the loading pattern and the condition of the intervertebral discs. There are many clinical and
biomechanical studies focusing on the consequences of facet
joint resection.
The biomechanical and kinetics of graded facetectomy was studied by many authors in both fresh cadavers
and finite element models studies.(22, 25,26,32-34) Such
a resection may change both the load-bearing and motion
characteristics of the spine and accelerates segmental degeneration. Biomechanically, the excision of the supraspinous/interspinous ligaments and facetectomy greater than
50% affects the motion of the intervertebral joint and induces additional stress to the remaining components of the
spine.(22,25,26,32) Haher et al reported that destruction of
the facet joints establishes an alternate path of loading and
the load is transfered to the anulus and anterior longitudinal
ligament to support the spine.(22) An increase in annular
stress after aggressive posterior bony and ligamentous resection results in an accelerated degeneration of intervertebral discs.(25,26,32)
Table 3. Facet angles of the different levels in control and
patient group
Normal Group
Right 51º±1.6º
Left
50º±1.3º
Patient Group
53.4 º ±19.5
48.0 º ±13 .6
L4-5
Right
Left
41º±8.9º
41º±1.4º
52.0 º ±15.5
48.1º ±18.13
L5-S1
Right
Left
38º±1.8º
37º±1.6º
L3-4
55.0 º ± 12.74
47.8 º ± 9.01
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Postoperative lumbosacral instability
Volume 2: Issue 1
Similar results can be drawn from clinical studies,
too.(3,33,35,36) Shenkin and Hash reported six cases of
postlaminectomy instability (9.8%) after three years of
follow-up in 59 patients who underwent laminectomy and
facetectomy. They reported 6% and 15% of instability after
two level and more level laminectomy, respectively (33).
Similarly, Guigui et al, analysed the causes of postoperative
instability after surgery for lumbar spinal stenosis in
38 patients. They reported that in 25% of their cases,
postoperative destabilization (ie, total bilateral facetectomy
without fusion, wide laminectomy extended into the pars
interarticularis with resultant in isthmic fracture) was the
cause of failure.(35) Postoperative instability is not reported
only after total facetectomy, it can also occur after a limited
facet resection. Mullin et al reported a high rate of spinal
instability after laminectomy for lumbar spinal stenosis.(36)
They reported that 54% of cases showed radiographic signs
of instability after decompressive lumbar laminectomy with
medial facetectomy. The evidence of instability after limited
facetectomy may be attributed to the predisposing factors.
The results of the current study support the importance
of the facet joint integrity even in cases of lumbar disc herniation. Based on the aforementioned clinical and biomechanical studies, a bilateral resection of more than 50% of a facet
joint, or total unilateral facetectomy is not recommended.
Such a procedure requires addition of a spinal fusion and
fixation procedure.
It is of note that aggressive resection may result in
instability even in instrumented cases, if the extent of instrumentation is shorter than extent of decompression.
Etebar and Cahill (37) addressed the instability secondary
to decompression beyond the level of instrumentation. This
type of instability is caused by decompression-instrumentation mismatch, and requires a careful surgical planing.
tive instability. This type of instability may occur long time
after a fixation procedure (23,37-39), and is secondary to accelerated degeneration of the adjacent levels. This type led
some surgeons to use new treatment modalities such as dynamic spine fixation or lumbar arthroplasty. The long-term
results of these modalities, however, are not known.
Classification
Although there are comprehensive classifications of spondylolisthesis (40), there are only a few studies addressing postoperative instability classification. Sefter and McAfee (41),
classified postlaminectomy spondylolisthesis as preoperative listhesis, new spondylolisthesis, and iatrogenic listhesis.
Based on the results presented here, we propose a classification for postoperative lumbosacral instability according to
causes of instability (Table 4).
1A. Instability caused by overt preoperative instability.
It is clear that an overt preoperative instability is associated
with postoperative lumbosacral instability. This dictates the
surgeon to perform a spinal instrumentation in addition to
the primary procedure. However, missing the instability or
avoiding an instrumentation procedure will cause postoperative instability.
1B. Instability caused by predisposing factors (potential instability). Predisposing factors may increase the risk of
postoperative instability even after limited bony resection.
This type of instability can be called as potential instability.
In other words, there is no instability unless these cases undergo decompressive procedure. Therefore, before any decompressive procedure in cases with predisposing factor, a
careful preoperative planning is mandatory. Unfortunately,
still most surgeons do not routinely use instrumentation in
such cases.
2A. Instability caused by aggressive bony and ligamentouse resection. This type of instability is caused by aggressive facet, pars interarticularis and interspinous ligament
resections. Depending on the amount of osseoligamentous
resection and the presence or abscence of risk factors, this
type of instability may occur after a short time or a long time
after surgery. The limited decompression may decrease the
rate of this type of instability.
2B. Instability caused by adjacent level degeneration. It
is well known that there is an increased stress in the level adjacent to the instrumented level. Such a stress may result in
instability in long term. The preventive and treatment modalities are not standard. The use of dynamic systems may
decrease the percentage of this group.
2C.
Instability
caused
by
instrumentationdecompression mismatch. It is reported that aggressive
bony and ligamentous resection beyond (extended over)
the instrumented level may result in instability shortly
after instrumentation.(23,37) If this occurs, there is an
insrumentation-decompression mismatch. Therefore, one
should avoid further cranial or caudal bony and ligamentous
Postoperative Reasons
The results of the current study revealed that degeneration
related-instability forms only a small percent of postopera-
Table 4. The proposed classification for iatrogenic lumbosacral instability based on the cause of instability.
1.
2.
3.
Instability due to preoperative reasons
A. Overt instability
B. Potential instability (No overt instability: Presence
of predisposing factors facilitating instability)
Iatrogenic instability
a. Instability due to aggressive decompression
b. Instability due to adjacent level degeneration
c. Instability due to instrumentation-decompression
mismatch
Instability unrelated to primary surgery
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Naderi et al
Volume 2: Issue 1
decompression beyod the instrumented level. In other
words, all decompressed levels should be fixated.
In summary, iatrogenic lumbosacral instability is a
multifactorial situation. Preoperative factors such as overt
instability and the presence of factors predisposing instability, or the need for aggressive decompression may faciliate postoperative lumbosacral instability. The addition of a
lumbosacral fusion and instrumentation will decrease the
likelihood of postoperative instability and failed back surgery syndrome.
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Postoperative lumbosacral instability
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