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Lumbar Segmental Instability -
Current Concepts
Dr.PGopinathan
Asst Professor of Orthopaedics
Medical College Calicut
E-Mail: drpgopinath@yahoo.com
Addresses for Correspondence
Dr.PGopinathan
Asst Professor of Orthopaedics
Medical College Calicut
E-Mail: drpgopinath@yahoo.com
J.Orthopaedics 2005;2(1)e1
Introduction:
The diagnosis and the management of
lumbar segmental instability(LSI) is one of the difficult
problems for orthopaedics surgeons all over the world. The
primary concern of LSI is radicular pain and pain due to
instability. The intervertebral disc is the most stabilizing
structure of the spine. The reduction in the disc height results
in narrowing of the size of the intervetebral foramen and
results in root compression.The transverse diameter of the
foramen is only 7mm and the size of the L4 root is 6mm so there
is a critical area through which the root escapes. This can be
addressed to a certain extent by foraminotomy but total
correction of the fundamental pathologic processes is possible
only by maintaining the disc height. The purpose of this review
article is understand the current concept regarding the
diagnosis and management of lumbar segmental instability along
with the review of Author’s own experience
REVIEW:
Hicks GE etal concluded that they
agree with previous studies suggesting that segmental mobility
testing is not reliable. The prone instability test, generalized
Ligamentous laxity scale, and aberrant motion with trunk ROM
demonstrated higher levels of reliability.(1)
Diedrich etal inferred in their study that normal sagittal
alignment after single-level lumbar fusion can be achieved with
rectangular and 4 degrees -wedged cages(2) O’sullivan PBetal made the final conclusion
in their study that individuals with a clinical diagnosis of
lumbar segmental instability demonstrate an inability to
reposition the lumbar spine accurately into a neutral spinal
posture while seated. This finding provides evidence of a
deficiency in lumbar proprioceptive awareness among this
population.(3)
O’Sullivan etal inferred that, Lumbar
segmental instability is considered to represent a significant
sub-group within the chronic low back pain population. The
clinical diagnosis of this chronic low back pain condition is
based on the report of pain and the observation of movement
dysfunction within the neutral zone and the associated finding
of excessive intervertebral motion at the symptomatic level.(4)
Krismer M etal concluded that Several
authors have tried to define segmental lumbar instability. Their
definitions are, increased antero-posterior translation,
pathologic coupled motion, increased neutral zone, pathologic
instantaneous center of rotation describe some mechanic findings
occurring in the aging spine. However, there is no evidence that
they help to differentiate the pathologic entity of segmental
lumbar instability from the normal aging process. The most
important structure to maintain lumbar stability is the
intervertebral disc. In the third and fourth decade, more than
50 percent of specimen show peripheral tears of the anulus. It
was shown in animal experiments that these tears develop to
radial tears, which are accompanied by nuclear volume loss and
decreased height. The facets degenerate one or two decades
later. Corresponding with the loss of discal function, they
increasingly contribute to spinal stability It is recommended to
base the decision of lumbar fusion on a painful degenerated
disc, and additional findings promising a good result.(5)
KaigleAM etal inferred that, Segmental
instability in the lumbar spine is associated with abnormal
intervertebral motion. The majority of biomechanical studies
have examined the in vitro effects of transecting individual
stabilizing structures (i.e., intervertebral disc, facet joints,
and ligaments), and have not simultaneously considered the
effects of active musculature on spinal kinematics, which exist
in the in vivo environment. Also, few studies have evaluated the
kinematic behavior in the neutral region, for example, the
transition phase between flexion and extension. Because of the
direct attachment to the vertebrae, both passive and active
strain from the musculature influence the spinal kinematics in
normal or destabilized motion segments. Although increasing the
range of motion, stimulation of the musculature surrounding the
injured motion segment has a stabilizing effect by reducing
abrupt kinematic behavior, particularly in the neutral region
where the muscles are under reduced tension. A facetectomy
produces a paradoxical kinematic behavior, which enhances the
unstable condition of the motion segment. Surgical and
rehabilitative treatments for patients with segmental
instability need to consider the physiologic influences of the
spinal musculature. (6)
Murata M etal made the following findings
that they analyzed disc space height, angular displacement,
tilting movement, and horizontal displacement in 109 patients
with low back pain and/or sciatica, on plain radiographs of the
lumbar spine. These parameters were compared with the grade of
disc degeneration as evaluated by magnetic resonance imaging
with the aim of studying lumbar segmental instability. Disc
space height decreased in proportion to the grade of disc
degeneration. Angular displacement was significantly less with
severe disc degeneration, accompanied by a tendency to
stabilization of the motion segment. Tilting movement and
horizontal displacement did not correlate with the grade of disc
degeneration. Lumbar segmental instability was recognized at all
levels even in individuals who appeared to be normal or to have
mild disc degeneration. The incidence of lumbar segmental
instability at the L3-4 level was significantly higher in
patients with normal discs or mild disc degeneration. At the
L4-5 and L5-S levels it did not differ between different grades
of disc degeneration.(7)
Kalebo P etal inferred that the
translatory movements in the patients were composed of a
predominant anterior displacement in the compression view and a
smaller posterior movement in the traction view. Analysis of
sagittal rotation, ie, angulatory movements in the L5-S1
segment, resulted in no significant difference between the two
groups. Compression-traction radiography may detect pathologic
translatory movements, indicative of lumbar segmental
instability.(8)
Harris BM etal concluded that the anterior lumbar interbody
fusion, posterior lumbar interbody fusion, and combined
anterior-posterior spinal procedures are gaining wide acceptance
for the treatment of selected patients with segmental spinal
instability and spondylolisthesis with associated degenerative
changes.(9)
Iguchi T etal made the final coclusion in
their study that anterior lumbar interbody fusion, posterior
lumbar interbody fusion, and combined anterior-posterior spinal
procedures are gaining wide acceptance for the treatment of
selected patients with segmental spinal instability and
spondylolisthesis with associated degenerative changes. Each
fusion technique may have different effects on the overall
flexibility of the lumbar spine. The unilateral TLIF procedure
with adjunctive pedicular fixation is one variation of an
interbody fusion technique that requires less bony and soft
tissue dissection and minimizes nerve root manipulation compared
with other interbody fusion methods.
The presence of patients with excessive
angulation and translation in younger age groups suggests they
have a hypermobile segment with least degenerated discs.
Different predominant patterns of these radiologic factors may
reveal the probable aging process of the instability.(10)
Sciffman etal concludedthat bilateral
implantation of low-profile cages in this patient population led
to satisfactory outcomes. Subsidence and changes in lordosis
were minimal. Fusion rates were good, especially for one-level
cases. Patient satisfaction was relatively high, considering the
population consisted of 96% worker's compensation cases. With
proper surgical technique, bilateral low-profile cages can be
used effectively to treat patients with degenerative disc
disease.(11)
La RosaG etal made the inference that the findings support the
view that an interbody fusion confers superior mechanical
strength to the spinal construct; when posterolateral fusion is
the sole intervention, progressive loss of the extreme
correction can be expected. Such mechanical insufficiency,
however, did not influence clinical outcome.(12)
Patwardhan AG etal concluded that insertion
of an anterior lumbar interbody fusion cage has been shown to
reduce motion in a human spine segment in all loading directions
except extension. The "stand-alone" cages depend on compressive
preload produced by anular pretensioning and muscle forces for
initial stabilization. However, the effect that the in vivo
compressive preload generated during activities of daily living
has on the construct is not fully understood. This study tested
the hypothesis that the ability of the cages to reduce the
segmental motions in flexion and extension is significantly
affected by the magnitude of the externally applied compressive
preload. In contrast to the observed extension instability
under anular tension preload only, the two-cage construct
exerted a stabilizing effect on the motion segment (a reduction
in segmental motion) in flexion as well as extension under
externally applied compressive preloads of physiologic
magnitudes. The external compressive preload significantly
affected the stabilization provided by the cages. The cages
provided substantially more stabilization, both in flexion and
in extension, at larger preloads than at smaller preloads.
Clinical Relevance: The study suggests that the segment treated
with an anterior lumbar interbody fusion cage is relatively less
stable under conditions of low external compressive preload. The
magnitude of preload required to achieve stabilization with
stand-alone cages may be only partially achieved by anular
pretensioning. Since the magnitude of the preload across the
disc space due to muscle activity can vary with activities of
daily living, supplemental stabilization of the cage construct
may provide a more predictably stable environment for lumbar
spine fusion.(13)
OdaI etal inferred that it remains undetermined what types of
spinal instability require interbody support in posterior lumbar
reconstruction. For spinal instability with preserved anterior
load sharing, pedicle screw fixation alone is biomechanically
adequate, and interbody cages should not be used because they
further increase segmental motion at the adjacent segment.
However, Posterior stabilization alone provides insufficient
stability and high implant strain in case of damaged anterior
column. In such cases, additional interbody cages significantly
increase construct stiffness and decrease hardware strain.
However, they increase ROM at the adjacent segment as well.(14)
Luk KD etal stated that the lateral
radiographs of patients in flexion and extension are widely used
to obtain quantitative and qualitative data on lumbar
spondylolisthesis. Changes in lumbar disc height and segmental
translation in a group of patients with spondylolisthesis have
been demonstrated with the addition of traction and compression.
Erect flexion and prone traction radiographs represent the
extremes of subluxation and reduction of the olisthesis,
respectively, and the change in olisthesis seen between these
extremes is correlated with the change in disc area and the
intervertebral slip angle. Vertical laxity of the affected
functional spinal unit resulting from disc degeneration produces
laxity in the ligaments and disc anulus, allowing olisthetic
motion. Restoration of disc height in turn restores tension to
the soft tissues around the disc and results in a spontaneous
reduction of the subluxation. Restoration and maintenance of
disc height with a spacer or interbody fusion therefore is
recommended as a goal in the treatment of spondylolisthesis.
When spondylolytic spondylolisthesis involves a posterior column
deficiency, additional reconstruction of this column with
posterior instrumentation is recommended. Application of the
traction radiographic technique in planning for
spondylolisthesis reduction is discussed along with the
technique of stabilization(15)
Tay BB etal concluded that the lumbar
interbody arthrodesis is a surgical technique that results in
fusion of the anterior column of the spine. The indications for
this procedure have evolved over time, and current indications
include spinal deformity, segmental instability, and discogenic
low back pain. Arthrodesis in the interbody space can be
accomplished through anterior or posterior approaches to the
spine, and these techniques are discussed.(16).
Pitkanen MT etal inferred that the sliding
instability is strongly associated with various plain
radiographic findings. In mechanical back pain, functional
flexion-extension radiographs should be limited to situations
when symptoms are not explained by findings of plain radiographs
and/or when they are likely to alter therapy.(17)
LeeSW etal concluded that the spine
instability, a clinical condition that is common but difficult
to diagnose, has been suggested to involve a characteristic
change in the relation between vertebrae during motion.
Assessment of lumbar instability using functional radiographs is
controversial. Information regarding dynamic spine kinematics in
vivo is limited. The results from this study showed that the
newly developed technique is reliable. It may have potential
value for evaluating spine instability in clinical practice.(18)
Laohacharoensombat W etal made the following findings that the
Interspinous bursa is common in the older population. It has
been associated with degenerative lumbar diseases, aging and
anatomical distance between the spinous process. However, no
detailed exploration of the segmental instability as a cause of
bursal formation has been done.angular mobility is a possible
cause of interspinous bursa. On the contrary, the presence of
insterspinous bursa may be evidence of segmental hypermobility.(19)
Togawa D etal concluded that the use of
interbody fusion cages is gaining rapid acceptance, but there is
little histologic documentation of the nature of tissue within
successful human interbody fusion cages. Autogenous bone graft
was incorporated in these radiographically successful human
intervertebral body fusion cages. A few debris particles were
observed, but there was no histologic evidence of
particle-induced(20)
Fujiwara A etal inferred that the
degenerative processes in the disc and facet joints affect the
stability of the motion segment. The exact relations among disc
degeneration, facet joint osteoarthritis, and the kinematics of
the motion segment are not well defined in the literature.
Abnormal tilting movement on flexion and anteroposterior
translatory instability both had negative associations with
facet joint osteoarthritis. However, anterior translatory
instability was positively associated with disc degeneration and
facet joint osteoarthritis. Rotatory instability in the sagittal
plane and posterior translatory instability were not associated
with disc degeneration and facet joint osteoarthritis.(21)
.Tsantriozs A etal cocluded that the cages were introduced to
overcome the limitations of conventional allografts. Radiodense
cage materials impede radiographic assessment of the fusion,
however, and may cause stress shielding of the graft. The
biomechanical data did not suggest any implant construct to
behave superiorly either as a stand-alone or with supplemental
posterior fixation. The PLIF Allograph Spacer is biomechanically
equivalent to titanium cages but is devoid of the deficiencies
associated with other cage technologies. Therefore, the PLIF
Allograft Spacer is a valid alternative to conventional
cages.(22)
Axelsson P etal inferred that as evidenced
by the resulting olisthetic deformity and supported by the
outcome from prior investigations, spondylolysis is assumed to
induce spinal segmental instability/hypermobility. The
spondylolytic defect in pars interarticularis does not cause
permanent instability/hypermobility detectable in the adult
patient with low back pain and low-grade olisthesis(23).
Tsantriozs A etal concluded that the
differences between cages in flexion/extension and lateral
bending NZ are attributed to the severity of geometrical
cage-endplate surface mismatch. Stand-alone cage constructs
reduced ROM effectively, but the residual ROM present indicates
the presence of micromotion at the cage-endplate interface.(24)
Lu WW etal inferred that In the management
of lumbar spinal stenosis, wide decompressive laminectomy with
partial or total facetectomy has been the standard procedure for
multilevel nerve decompression. Main complications with these
procedures have been instability and chronic pain syndrome.
Multilevel fenestration with undermining enlargement of the
spinal canal has been selected for multilevel nerve
decompression in recent years. However, the biomechanical
effects of multilevel fenestration and discectomy have been
controversial and difficult to validate. This study investigated
the in vitro biomechanical effects of multilevel fenestrations
and discectomies on motion behavior of the whole lumbar spine
CONCLUSIONS: The results demonstrate that multilevel
fenestrations and discectomies affect lumbar spinal stability in
flexion, but have no effect on the stability of the lumbar spine
in lateral bending or axial rotation.(25)
Kotilainen etal made tha findings that, comfirming earlier
observations, the findings of their study support the concept
that patients with postoperative lumbar instability have a poor
prognosis. Further studies are needed to define the optimal
treatment for this problematic patient group.(26)
Shono etal concluded that recently, many
adverse effects have been reported in fusion augmented with
rigid instrumentation. Only few reports are available regarding
biomechanical effects of stability provided by spinal
instrumentation and its effects on residual adjacent motion
segments in the lumbar-lumbosacral spine. However, segmental
displacement at the site of simulated instability becomes more
obvious. Application of segmental instrumentation changes the
motion pattern of the residual intact motion segments, and the
changes in the motion pattern become more distinct as the
fixation range becomes more extensive and as the rigidity of the
construct increases.(27)
Tekeoglu etal concluded that the
gravitational traction is performed by suspending the patient in
a hanging, upright position for an extended period of time. In
spite of disagreement among authors about the effect of lumbar
traction, recent innovations have enabled the distraction of
vertebrae Gravitational traction had a very apparent effect on
intervertebral space and was found to be an effective method to
distract lumbar vertebrae. Discomfort experienced by the patient
during suspension may be overcome by making biomedical changes
to the suspension corset.(28)
The author’s preferred method is that
maintenance of the disc space is the most important factor in
treating the LSI.(29).
CONCLUSIONS
Lumbar segmental instability is one of the difficult problems to
spine surgeons all over the world. The standard clinical tests
including prone instability test and stress radiography will
help in a long way to make a clinical diagnosis. Identification
of the individual problem which results in a particular symptom
and addressing each one of them individually will give
symptomatic relief and patient satisfaction. Posterior
instrumentation and fusion alone may not always result in
biomechanical stability. Combined anterior and posterior fusion
will stabilize the spine in a clinically useful manner
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29 DrPGopinathan DrAnwarMH Dr Yassir Hussain Physiologic
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lumbar segmental instability JCOA 2004 vol2 No4 62 -66
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