Traumatic Shoulder Instability.
Last updated Thursday, February 10, 2005
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Figure 1 - Torque equilibrium
Figure 2 - Anterior glenohumeral ligament
Figure 3 - Glenoid abutts against the insertion of the cuff
About traumatic instability
What is traumatic glenohumeral instability (TUBS)?
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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What are the associated pathologies of traumatic instability of the shoulder?
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.
What does TUBS mean?
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.
What are SLAP (superior labrum, anterior to posterior) lesions and how are they managed?
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.
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