Rotational Instability Of the Midthoracic Spine Assessment and Management
Diane Lee. Published in Manual Therapy 1(5): 234-291
Diane Lee BSR FCAMT, Wednesday 29 March 2006 - 03:47:53

Recent research has enhanced the understanding of instability
of the spine. The principles of this research has been incorporated into the
evaluation and treatment of the unstable thorax. Rotational instability of
the midthorax is commonly seen following trauma to the chest. Specific mobility
and stability tests have been developed to detect this instability. The tests
are derived from a biomechanical model of evaluation. Treatment is based on
sound stabilization principles and although the segment will remain unstable
on passive testing, the patient can be trained to control the biomechanics
of the thorax and return to a high level of function.

Introduction

In the literature pertaining to back pain, the musculoskeletal components
of the thorax have received little attention. Research is sparse in all areas
including developmental anatomy, normal biomechanics, pathomechanical processes,
evaluation and treatment. And yet, midback pain is not uncommon. A biomechanical
approach to assessment and treatment of the thorax requires an understanding
of its normal behavior. A working model has been proposed (Lee 1993, 1994a,b)
part of which is based on scientific research (Panjabi 1976) and the rest on
clinical observation. This model requires validation through further research
studies.

The understanding of instability of the spine has been enhanced by recent
research (Hides et al 1994, 1995, Hodges & Richardson 1995a,b, Panjabi
1992a,b, Richardson & Jull 1995, Vleeming et al 1995). The principles of
this research have been incorporated into the evaluation and treatment of the
unstable thorax. Rotational instability of the midthorax involves both the
spinal and costal components of the segment. Specific tests have been developed
(Lee 1993, 1994a,b, Lowcock 1990) to detect this instability and the management
is based on sound stabilization principles (Richardson & Jull 1994).

Anatomy

The thorax can be divided into four regions according to anatomical and biomechanical
differences. The midthorax is the topic of this paper and includes the T3 to
T7 vertebrae, the third to seventh ribs and the sternum. Rotational instability
of the thorax is most common in this region. A brief anatomical review is relevant
in order to understand the normal mechanics and pathomechanics of rotation
in the midthorax.

The facets on both the superior and inferior articular processes of the thoracic
vertebra are curved in both the transverse and sagittal planes (Davis 1959).
This orientation permits multidirectional movement and does not restrain, nor
direct, any coupling of motion when the thorax rotates. Neither do they limit
the amount of lateral translation which occurs in conjunction with rotation
(Panjabi 1976). The ventral aspect of the transverse process contains a deep,
concave facet for articulation with the rib of the same number. This curvature
influences the conjunct rotation which occurs when the rib glides in a superoinferior
direction. A superior glide is associated with anterior rotation of the rib,
an inferior glide is associated with posterior rotation.

The posterolateral corners of both the superior and inferior aspects of the
vertebral body contain an ovoid demifacet for articulation with the head of
the rib. Development of the superior costovertebral joint is delayed until
early adolescence (Penning & Wilmink 1987, Warwick et al 1989). In the
skeletally mature, the costovertebral joint is divided into two synovial cavities,
separated by an intra-articular ligament. Several ligaments support the costovertebral
complex including; the radiate, costotransverse or interosseous ligament, lateral
costotransverse ligament and the superior costotransverse ligament. Attenuation
of some of these ligaments occurs when the midthorax is unstable.

The anatomy and age related changes of the intervertebral disc in the thorax
have received recent study. Crawford (1995) investigated a series of 51 cadavers
aged from 19 to 91 and tabulated the incidence and location of degeneration,
Schmorl’s nodes and posterior intervertebral disc prolapse. The midthoracic
region was found to have the highest incidence of degenerated discs and intervertebral
prolapses. Wood et al (1995) found that 73% of ninety asymptomatic individuals
had positive anatomical findings at one or more levels of the thoracic spine
on magnetic resonance imaging. These findings included herniation, bulging,
annular tears, deformation of the spinal cord and Scheuermann end-plate irregularities.
While structural changes are common, their clinical consequences are unknown.
It is hypothesized (Lee 1993, 1994a,b) that some changes must take place in
the intervertebral disc for the thoracic segment to become unstable in rotation.
These changes may occur prior to the onset of symptoms and predispose the patient
to the development of instability.

Biomechanics of rotation

In the cadaver, Panjabi et al (1976) found that rotation around a vertical
axis was coupled with contralateral sideflexion and contralateral horizontal
translation. Clinically, it appears that in the midthorax, midrange rotation
can couple with either contralateral or ipsilateral sideflexion. At the limit
of rotation, however, the direction of sideflexion has consistently been found
to be ipsilateral. In other words, at the limit of axial rotation, rotation
and sideflexion occur to the same side. It may be that the thorax must be intact
and stable both anteriorly and posteriorly for this in vivo coupling of motion
to occur. The anterior elements of the thorax were removed 3 cm lateral to
the costotransverse joints in the study by Panjabi et al (1976).

During right rotation of the trunk, the following biomechanics are proposed
(Lee 1993, 1994a,b). The superior vertebra rotates to the right and translates
to the left . Right rotation of the superior vertebral body 'pulls' the superior
aspect of the head of the left rib forward at the costovertebral joint inducing
anterior rotation of the neck of the left rib (superior glide at the left costotransverse
joint), and 'pushes' the superior aspect of the head of the right rib backward,
inducing posterior rotation of the neck of the right rib (inferior glide at
the right costotransverse joint). The left lateral translation of the superior
vertebral body 'pushes' the left rib posterolaterally along the line of the
neck of the rib and causes a posterolateral translation of the rib at the left
costotransverse joint. Simultaneously, the left lateral translation 'pulls'
the right rib anteromedially along the line of the neck of the rib and causes
an anteromedial translation of the rib at the right costotransverse joint.
An anteromedial/posterolateral slide of the ribs relative to the transverse
processes to which they attach is thought to occur during axial rotation.

When the limit of this horizontal translation is reached, both the costovertebral
and the costotransverse ligaments are tensed. Stability of the ribs both anteriorly
and posteriorly is required for the following motion to occur. Further right
rotation of the superior vertebra occurs as the superior vertebral body tilts
to the right (glides superiorly along the left superior costovertebral joint
and inferiorly along the right superior costovertebral joint). This tilt causes
right sideflexion of the superior vertebra at the limit of right rotation of
the midthoracic segment .

Definition of instability

Instability can be defined as a loss of the functional integrity of a system
which provides stability. In the thorax, there are two systems which contribute
to stability - the osteoarticularligamentous and the myofascial. Snijders & Vleeming
(Snijders et al 1992, Vleeming et al 1990a,b, 1995) refer to these two systems
as form and force closure. Together they provide a self-locking mechanism which
is useful in rehabilitation.

“Form closure refers to a stable situation with closely fitting joint
surfaces, where no extra forces are needed to maintain the state of the system.” (Snijders
et al 1992, Vleeming et al 1995). The degree of inherent form closure of any
joint depends on its anatomy. There are three factors which contribute to form
closure; the shape of the joint surface, the friction coefficient of the articular
cartilage and the integrity of the ligaments which approximate the joint. The
costal components of the midthorax have considerable form closure given the
shape of the costovertebral joints and the structure of the ligaments.

“In the case of force closure, extra forces are needed to keep the object
in place. Here friction must be present.” (Snijders et al 1992). Joints
with predominantly flat surfaces are well suited to transfer large moments
of force but are vulnerable to shear. Factors which increase intraarticular
compression will increase the friction coefficient and the ability of the joint
to resist translation. The relatively flat zygapophyseal joints provide little
resistance to lateral translation and rely on the form closure of the costal
components and the myofascial force closure for stability. The muscles which
contribute to force closure of the midthoracic region include the transversospinalus
and erector spinae groups. These muscles will be addressed in rehabilitation
of the unstable thorax.

Panjabi has proposed a conceptual model which describes the interaction between
the components of the spinal stabilising system (Panjabi 1992a,b). In this
model, he describes the neutral zone which is a small range of displacement
near the joint’s neutral position where minimal resistance is given by
the osteoligamentous structures. The neutral zone can be palpated during specific
tests for stability. The range of the neutral zone may increase with injury,
articular degeneration (loss of form closure) and/or weakness of the stabilising
musculature (loss of force closure). When the thorax is unstable, the neutral
zone is increased.

Rotational instability of the thorax causes an increase in the neutral zone
which is palpated during segmental lateral translation. The unstable segment
has a softer end feel of motion, an increased quantity of translation and a
variable symptom response. If the joint is irritable, the test may provoke
pain. If the instability is long standing and asymptomatic, the tests are often
not provocative.


Clinical tests for lateral translation stability (rotation)

To evaluate the stability of a midthoracic segment, it is necessary to first
determine the available mobility in lateral translation. Left rotation/left
sideflexion/right translation requires the left sixth rib to glide anteromedially
relative to the left transverse process of T6 and the right sixth rib to glide
posterolaterally relative to the right transverse process of T6 and the T5
vertebra to laterally translate to the right relative to T6. This motion is
tested in the following manner. The patient is sitting with the arms crossed
to opposite shoulders. 5). With the right hand/arm, the thorax is palpated
such that the fifth finger of the right hand lies along the sixth rib. With
the left hand, the transverse processes of T6 are fixed. With the right hand/arm
the T5 vertebra and the sixth ribs are translated purely to the right in the
transverse plane. The quantity, and in particular the end feel of motion, is
noted and compared to the levels above and below.

Next, the stability of the T5-6 spinal component can be evaluated by restricting
the sixth ribs from gliding relative to their transverse processes and then
applying a lateral translation force. No motion should occur when the ribs
are fixed. This test stresses the anatomical structures which resist horizontal
translation between two adjacent vertebrae when the ribs between them are fixed.
A positive response is an increase in the quantity of motion and a decrease
in the resistance at the end of the range. To test the T5-6 segment, the patient
is sitting with the arms crossed to opposite shoulders. With the right hand/arm,
the thorax is palpated such that the fifth finger of the right hand lies along
the fifth rib. With the left hand, T6 and the sixth ribs are fixed bilaterally
by compressing the ribs centrally towards their costovertebral joints. The
T5 vertebra is translated through the thorax purely in the transverse plane.
The quantity of motion, the reproduction of any symptoms and the end feel of
motion is noted and compared to the levels above and below. When the segment
is stable, no motion should occur. When unstable, the same degree of motion
previously noted in the mobility test can be palpated.

Subjective and objective findings

Rotational instability of the midthorax can occur when excessive rotation
is applied to the unrestrained thorax or when rotation of the thorax is forced
against a fixed rib cage (seat belt injury). At the limit of right rotation
in the midthorax, the superior vertebra has translated to the left, the left
rib has translated posterolaterally and the right rib has translated anteromedially
such that a functional U joint is produced. Further right rotation results
in a right lateral tilt of the superior vertebra. Fixation of the superior
vertebra occurs when the left lateral translation exceeds the physiological
motion barrier and the vertebra is unable to return to its neutral position.

Initially, the patient complains of localized, central midthoracic pain which
can radiate around the chest wall. The pain may be associated with numbness
along the related dermatome. Sympathetic symptoms including sensations of local
coldness, sweating, burning and visceral referral are common. If the unstable
complex is fixated at the limit of rotation, very little relieves the pain.
All movements, especially contralateral rotation, and sustained postures tend
to aggravate the pain. If the complex is not fixated, the patient often finds
that contralateral rotation and extension affords some relief.

Positionally, the following findings are noted when T5-6 is fixated in left
lateral translation and right rotation (right rotational instability). T5﷓T6
is right rotated in hyperflexion, neutral and extension, the right sixth rib
is anteromedial posteriorly and the left sixth rib is posterolateral posteriorly.
All active movements produce a 'kink' at the level of the fixation, the worst
movement is often rotation . The passive accessory mobility tests for the zygapophyseal
and costotransverse joints are reduced but present. The right lateral translation
mobility test is completely blocked.

Prior to reduction of the fixation, the left lateral translation stability
test of T5-6 is normal because the joint is stuck at the limit of left lateral
translation. After the fixation is reduced, the stability test reveals the
underlying excessive left lateral translation. The reduction restores the complex
to a neutral position from which the amplitude of left lateral translation
can be more effectively measured.

If the segment is not fixated at the limit of lateral translation, then both
the mobility and stability tests will reveal excessive left lateral translation.
When the sixth ribs are compressed medially into the vertebral body of T5,
there should be no lateral translation of T5 relative to T6. When the segment
is unstable, excessive motion during this test is noted.

Segmental atrophy of multifidus can be palpated bilaterally. In the lumbar
spine, Hides et al (1994) found wasting and local inhibition at a segmental
level of the lumbar multifidus muscle in all patients with a first episode
of acute/subacute low back pain. In a follow-up study (Hides et al 1995), they
found that without therapeutic intervention, multifidus did not regain its
original size or function and the recurrence rate of low back pain over an
eight month period was very high. They also found that the deficit could be
reversed with an appropriate exercise program. This research is consistent
with clinical observation of instability in the midthorax.

Treatment

If the segment is fixated at the limit of lateral translation/rotation, a
manipulative reduction is necessary prior to the initiation of a stabilization
program. When T5-6 is fixated in left lateral translation/right rotation the
following technique is used.

The patient is in left sidelying, the head supported on a pillow and the arms
crossed to the opposite shoulders. With the left hand, the right seventh rib
is palpated posteriorly with the thumb and the left seventh rib is palpated
posteriorly with the index or long finger. T6 is fixed by compressing the two
seventh ribs towards the midline. Care must be taken to avoid fixation of the
sixth ribs which must be free to glide relative to the transverse processes
of T6. The other hand/arm lies across the patient's crossed arms to control
the thorax. Segmental localization is achieved by flexing and extending the
joint until a neutral position of the zygapophyseal joints is achieved. This
localization is maintained as the patient is rolled supine only until contact
is made between the table and the dorsal hand.

From this position, T5 and the left and right sixth ribs are translated laterally
to the right through the thorax to the motion barrier. Strong longitudinal
distraction is applied through the thorax prior to the application of a high
velocity, low amplitude thrust. The thrust is in a lateral direction in the
transverse plane . The goal of the technique is to laterally translate T5 and
the left and right sixth ribs relative to T6. Following reduction of the fixation,
the thorax is taped to remind the patient to avoid end range rotation. Stabilization
is then required.

If the segment is not fixated, stabilization is begun immediately. Physiotherapy
cannot restore form closure therefore the emphasis of treatment must be on
the restoration of force closure. The goal is to reduce the dynamic neutral
zone during functional activities and to avoid the end ranges of rotation thus
limiting the chances of fixation. This is accomplished through specific exercises
augmented with muscle stimulation and EMG. The first group of muscles which
must be addressed are the transversospinal (multifidus) and erector spinae
groups.

Essentially, the patient is taught to specifically recruit the segmental muscles
isometrically and then concentrically while prone over a gym ball. Electrical
stimulation can be a useful adjunct at this time. In sidelying, specific segmental
rotation can be resisted by the therapist both concentrically and eccentrically
to facilitate the return of multifidus function. The program is progressed
by increasing the load the thorax must control. Initially, scapular motion
is introduced, in particular lower trapezius work. The patient must control
the neutral position of the midthorax throughout the scapular depression. The
goal is to teach the patient to isolate scapular motion from spinal motion
so that the scapula does not produce spinal motion during activities involving
the arm. Once control is gained over the scapula, exercises involving the entire
upper extremity may be added. By increasing the lever arm and then the load,
the midthorax is further challenged. Gymnastic ball, proprioceptive, balance
and resistive work can be integrated into the program as needed. The velocity
of the exercises can be increased according the patient’s work and recreation
demands. Initially, the load should be applied bilaterally and then progressed
to unilateral work. At the completion of the program, the patient should be
able to isolate specific spinal extension without scapular motion and control
both bilateral and unilateral arm motion throughout midrange. They are advised
to avoid any activity which places the midthorax at the limit of rotation in
the direction of their instability.

Conclusion

Instability of the thorax can be extremely debilitating but is a treatable
condition. The segment remains statically unstable and the neutral zone, on
passive testing, remains increased. Through appropriate training, the region
can become dynamically stable and the neutral zone controlled.

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Posted by Mart de Kruijff, BSc. PT, MAS.O.M.T.



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