Traumatic Shoulder Instability.
Last updated Thursday, February 10, 2005
Figure 1 - Torque equilibrium Figure 2 - Anterior glenohumeral ligament Figure 3 - Glenoid abutts against the insertion of the cuff Figure 4 - Age at presentation of traumatic instability patients Figure 5 - Functional impairment among TUBS patients Figure 6 - Glenoid abutting against the cuff insertion to the head posteriorly About traumatic instabilitySummary Traumatic instability (TUBS) is instability that arises from an
force large enough to injure some of the major supporting structures of
the joint, such as the glenohumeral capsule, ligaments, rotator cuff,
or the bone of the humerus or glenoid.
Usually, traumatic instability arises from a fall on the
outstretched hand, for example in skiing, football, or wrestling. In
addition to a careful history and clinical examination, X-rays may be
helpful in evaluating the patient with traumatic instability.
When the instability happens repeatedly or when fear of recurrent dislocation interferes with normal use of the shoulder, surgical repair of the injury can be considered. The postoperative care after this surgery is very important.
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Associated pathologies The most common pathology associated with traumatic instability is
the avulsion of the anteroinferior capsule and ligaments from the
glenoid rim. Substantial force is required to produce this avulsion in
a healthy shoulder. While this load may be applied directly (for
example, by having the proximal humerus hit from behind), an indirect
loading mechanism is more common. Indirect loading is most easily
understood in terms of a simple model of the torques involved. When the
upper extremity is abducted and externally rotated by a force applied
to the hand, the following equation for torque equilibrium is a useful
approximation, if we attribute the major stabilizing role to the
ligament: I x R = F x A or equivalently I = F x A/R, where "I" is the
tension in the inferior glenohumeral ligament, "R" is the radius of the
humeral head, "F" is the abduction external rotation load applied to
the hand, and "A" is the distance from the center of the humeral head
to the hand. If the radius of the humeral head is 2.5 cm and the
distance from the head center to the hand is one meter, this formula
suggests that the inferior glenohumeral ligament would experience a
load 40 times greater than that applied to the hand. From this example
we can see that a much lesser load is required to produce the
characteristic lesion of traumatic instability if this load is applied
indirectly through the lever arm of the upper extremity.
Avulsion of the anterior glenohumeral ligament mechanism deprives
the joint of stability in positions where this structure is a major
stabilizer of the joint, which is typically approaching maximal
external rotation and extension of the arm elevated near the coronal
plane. These are positions in which stability is dependent on integrity
of the capsuloligamentous mechanism. Thus, it is evident that in
recurrent traumatic instability, problems are most likely to occur when
the arm is placed in a position approximating that in which the
original injury occurred. Midrange instability may also result from a
traumatic injury if the glenoid concavity is compromised by avulsion of
the labrum or fracture of the bony lip of the glenoid. Lessening of the
effective glenoid depth compromises the effectiveness of concavity
compression, reduces the angles through which the glenoid can balance
the net joint reaction force, reduces the surface available for
adhesion-cohesion, and compromises the ability of the glenoid suction
cup to conform to the head of the humerus.
The corner of the glenoid abuts against the insertion of the cuff to
the tuberosity when the humerus is extended, abducted, and externally
rotated. Thus, the same forces involved in challenging the strength of
the inferior glenohumeral ligament are also applied to the greater
tuberosity-cuff insertion area. It is not surprising, therefore, that
tuberosity fractures and cuff injuries may be a part of the clinical
picture of traumatic instability. The exact location and type of
traumatic injury depends on the age of the patient and the magnitude,
rate, and direction of force applied. Avulsions of the glenoid labrum
and glenoid rim fractures are more commonly seen in young individuals
after a major injury. In patients over the age of 35, traumatic
instability tends to be associated with fractures of the greater
tuberosity and rotator cuff tears. This tendency increases with
increasing age at the time of the initial traumatic dislocation. Thus,
as a rule, younger patients require management of anterior lesions and
older patients require management of posterior lesions.
The posterior lateral humeral head defect is a common feature of
traumatic instability. These lesions are often noted after the first
traumatic dislocation and tend to increase in size with recurrent
episodes. This impaction injury occurs when the anterior corner of the
glenoid is driven into the posterior lateral humeral articular surface.
It is evident that this injury is close to the cuff insertion. Large
head defects compromise stability by diminishing the articular
congruity of the humerus. TUBS syndrome We refer to the usual type of traumatic instability as the TUBS
syndrome because it arises from a significant episode of Trauma,
characteristically from abduction and extension of the arm elevated in
the coronal plane. The resulting instability is usually Unidirectional
in the anteroinferior direction. The pathology is usually an avulsion
of the capsuloligamentous complex from the anterior inferior lip of the
glenoid, commonly referred to as a Bankart lesion. With functionally
significant recurrent traumatic instability, a Surgical repair of this
ligament avulsion is frequently required to restore function. We have
established some diagnostic criteria for making this diagnosis. SLAP lesions SLAP lesions (superior labrum, anterior to posterior) are
detachments of labrum (the lining of the glenoid socket of the
shoulder). In many cases it is difficult to tell if the labral
attachment is normal or not--even with arthroscopy. Thus it is
important that the surgeon and the patient be able to relate the
symptoms to the finding on arthroscopy. This is a particular challenge
because there are no symptoms or presurgical tests that reliably
establish the presence of a symptomatic SLAP lesion.
Surgery can either trim the labrum or attempt to reattach it.
After this surgery, the patient experiences the same type of
discomfort as after other arthroscopic surgeries. The details of the
recovery and rehabilitation depend on the specifics of the surgery. For
example, if there is a trimming, early motion may be carried out,
while, after a repair, a period of restricted use may be in order until
healing has occurred. The initial episode Traumatic instability commonly begins with an injury when the
patient is between 14 and 34 years of age. In suspected recurrent
instability from a traumatic cause, the most important element in the
history is the definition of the original injury. As is evident to
anyone who has attempted to recreate these lesions in a cadaver,
substantial force is required to produce a traumatic dislocation. In
characteristic anterior traumatic instability, the structure that is
avulsed is the strongest part of the shoulder's capsular mechanism: the
anterior inferior glenohumeral ligament. In order to tear this
ligament, substantial force needs to be applied to the shoulder when
the arm is in a position to tighten this ligament. Thus the usual
mechanism of injury involves the application of a large
extension-external rotation force to the arm elevated near the coronal
plane. Such a mechanism may occur in a fall while snow skiing or while
executing a high speed cut in water skiing, in an arm tackle during
football, with a block of a volleyball or basketball shot, or in
relatively violent industrial accidents with the arm in this position.
Awkward lifting and rear-end automobile accidents would not be expected
to provide the conditions or mechanism for this injury. We find that
direct questioning and persistence are often required to elicit a full
description of the initial mechanism of injury including the position
of the shoulder and the direction and magnitude of the applied force at
the time of the initial injury. Yet this information is critical to
establishing the diagnosis.
An initial traumatic dislocation often requires assistance in
reduction, rather than reducing spontaneously as is usually the case in
atraumatic instability. Radiographs from previous emergency room visits
may be available to show the shoulder in its dislocated position.
Axillary or other neuropathy may have accompanied the glenohumeral
dislocation. Any of these findings individually or in combination
support the diagnosis of traumatic as opposed to atraumatic
instability.
Traumatic instability may occur without a complete dislocation. In
this situation, the injury produces a traumatic lesion, but this lesion
is insufficient to allow the humeral head to completely escape from the
glenoid. The shoulder may be unstable because, as a result of the
injury, it manifests apprehension or subluxation when the arm is placed
near the position of injury. In these cases there is no history of the
need for reduction nor radiographs with the shoulder in the dislocated
position. Thus the diagnosis rests to an even greater extent on a
careful history that focuses on the position and forces involved in the
initial episode. Subsequent episodes Characteristically, the shoulder with traumatic instability is
comfortable when troublesome positions are avoided. However, the
shoulder often remains vulnerable to recurrent episodes of instability.
These may range from sensations of apprehension or impending
dislocation to recurrent complete dislocations requiring manipulative
reduction. In this context, recurrent episodes of instability occur
most commonly when the shoulder is forced unexpectedly into the
abducted externally rotated position or during sleep when the patient's
active guard is less effective. There may be a history of increasing
ease of dislocation. We determine whether the patient is reluctant to
carry out certain activities or to put the arm in certain positions
because of fear of instability. This apprehension may interfere with
the patient's ability to use the arm for work, activities of daily
living, or sports.
The history must seek to demonstrate the position and forces
involved in the initial and subsequent episodes of instability. The
examiner must be convinced that these are appropriate and sufficient to
tear the normally strong capsuloligamentous structures which stabilize
the shoulder at the extremes of motion. This careful history is the
foundation on which the diagnosis of traumatic instability rests.
Functional evaluation The results from the Simple Shoulder Test
evaluations of patients with traumatic anterior glenohumeral
instability show that the most consistent functional impairment was the
inability to throw overhand, but many patients also had problems
sleeping, putting their hand behind their head, and lifting a gallon to
head level.Physical examination The goal of the physical examination is largely to confirm the
impression obtained from the history: that a certain combination of arm
position and force application produces the actual or threatened
glenohumeral instability that is of functional concern to the patient.
If the diagnosis has been rigorously established from the history, for
example by documented recurrent anterior dislocations, it is not
necessary to risk redislocation on the physical examination. If such
rigorous documentation is not available, however, we must challenge the
ligamentous stability of the shoulder in the suspected position of
vulnerability. We seek to have the patient identify the positions and
events that are of functional significance.
The most common direction of recurrent traumatic instability is
anteroinferior. Stability in this position is challenged by externally
rotating and extending the arm elevated in the coronal plane. This is
conveniently done in the supine position with one of the examiner's
hands under the back of the shoulder serving as a fulcrum for the
external rotation and extension force. We apply extension and external
rotation loads in different positions of elevation to challenge the
various parts of the anterior capsular mechanism. The patient will very
often guard against the position of instability by actively limiting
the range of humeroscapular motion. For this reason, we may need to
hold the arm in the challenging position for 1 to 2 minutes to fatigue
the stabilizing musculature. When the muscle stabilizers tire, the
capsuloligamentous mechanism is all that is holding the humeral head in
the glenoid. At this moment the patient with traumatic anterior
instability becomes apprehensive, recognizing that the shoulder is
about to come out of joint. This recognition is strongly supportive of
the diagnosis of traumatic anterior instability.
Standard tests of glenohumeral laxity are of limited value in the
diagnosis of traumatic instability. As has been described earlier the
magnitude of translation on the standard test of glenohumeral laxity
does not distinguish stable from unstable shoulders. The magnitude of
translation on some clinically stable shoulders may be as great or
greater than that on shoulders with traumatic instability. However, the
experienced examiner may detect certain findings such as increased ease
of translation on the anterior drawer test or grinding as the humeral
head slides over a bony edge of the glenoid from which the labrum has
been avulsed. There may also be a catching or a locking of a torn
glenoid labrum, producing findings analogous to those of a torn
meniscus in the knee.
We do not consider pain on abduction, external rotation and
extension to be specific for instability. Such pain may relate to
shoulder stiffness or alternatively to abutment of the glenoid against
the cuff insertion to the head posteriorly. Furthermore, relief of this
pain by anterior pressure on the humeral head may result from
diminished stretch on the anterior capsule or from relief of the
abutment posteriorly.
In all patients with traumatic instability but particularly in those
over age 35, the strength of the internal and external rotation must be
examined. With increasing age, there is an increasingly common
association between traumatic glenohumeral instability and rotator cuff
defects. Patients with significant cuff lesions may demonstrate atrophy
of the spinatus muscles as well as pain and or weakness on resisted
abduction or external rotation. Any rotator cuff pathology must be
recognized and incorporated in the treatment plan.
Finally, carefully examine the brachial plexus to assure that the
episodes of traumatic instability have not compromised its function. Radiographs Radiographs frequently help to provide confirmation of traumatic
glenohumeral instability. These findings may include an indentation or
impaction in the posterior aspect of the humeral head from contact with
the anteroinferior corner of the glenoid when the joint is dislocated.
Radiographs may also reveal a periosteal reaction to the ligamentous
avulsion at the glenoid lip or occasionally a fracture of the glenoid
rim.
These lesions are usually revealed by an anteroposterior view in the
plane of the scapula, a proper axillary view, and an apical oblique
view, as shown in the example movie listed below. We have not found
additional radiographic views, CT arthrography, or MRI to be cost
effective in the evaluation of shoulders with characteristic traumatic
instability. We occasionally use CT to define the magnitude of bone
loss when a sizable humeral head or glenoid defects have been
identified on a series of plain radiographs.
In a patient whose onset of traumatic instability occurred after age
35 there may be evidence on history and physical examination of rotator
cuff pathology. In these situations, preoperative imaging of cuff
integrity may play an important role in surgical planning: the approach
for rotator cuff repair is quite different than the approach for the
repair of an anterior inferior capsular lesion.
Electromyography may be helpful in the evaluation of the patient
with recurrent traumatic instability if the history and physical
examination suggest residual brachial plexus lesions.
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Management options A patient with traumatic anterior glenohumeral instability has
symptoms of instability (apprehension, subluxation, or dislocation)
when the arm is elevated near the coronal plane, extended, and
externally rotated. Characteristically the shoulder is relatively
asymptomatic in other extreme positions or in midrange positions.
Thus, for some patients appropriate management may consist solely of
education about the nature of the lesion and identification of the
positions and activities that need to be avoided. Strengthening the
shoulder musculature may help prevent the shoulder being forced into
positions of instability. The exercise program suggested for atraumatic instability
may be considered as an option for traumatic instability as well.
"Training tape" may be applied to the anterior aspect of the shoulder
as a reminder to avoid abduction, external rotation, and extension
ofthe shoulder. However, many patients with refractory symptoms will
wish to consider surgical repair.
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