Functional Shoulder Instability

Functional Shoulder Instability

(FSI) is a condition mainly caused by pathologic muscle activation patterns instead of structural defects.

Postional Functional Shoulder Instability:

1-Positional FSI involves subluxations or dislocations caused by movement of the affected arm in a certain position and spontaneous reduction once the position is left again.

2-Positional FSI can either be controllable or noncontrollable.

A-Controllable means that subluxations or dislocations can voluntarily be caused by the patients by executing certain movements. It creates little discomfort or functional impairment because it can be suppressed by the patient if wanted.

B-Noncontrollable means that subluxations or dislocations occur involuntarily during movement of the arm. It can lead to severe loss of function, discomfort, and pain because it cannot be countered by the patient. The typical movement during which posterior positional FSI can be observed is horizontal flexion and internal rotation. It causes a posterior subluxation or dislocation, which, for the observer, is often hardly noticeable. Subsequent horizontal extension leads to reduction of the joint, which is typically visible for the examiner as a result of an abrupt contour change of the posterior aspect of the shoulder sometimes accompanied by a “popping” noise.

The typical movement during which anterior positional FSI can be observed is abduction and external rotation. The movement causes a subluxation or dislocation of the humeral head, which is visible as bulging in the axilla.?Reduction is obtained by returning to a neutral position. Posterior positional FSI was by far the most commonly observed type of FSI . Anterior positional FSI seems to be much less frequent.

Non-positional Functional Shoulder Instability:

Non-positional FSI involves subluxations or dislocations of the shoulder in neutral or close to neutral position of the arm. In contrast to positional instability, it is not caused by certain arm movements but rather seems to be caused by pathologic muscle contractions that lead to a temporary dislocation of the humeral head.

This form of FSI also can be controllable or noncontrollable. In the case of a?controllable nonpositional FSI, patients often have no functional impairment. In contrast,?noncontrollable nonpositional FSI is a very severe form of shoulder instability that can completely impair normal shoulder function. Repetitive subluxations, dislocations, or sometimes even static dislocations in various directions are sustained even with the arm in neutral rotation because of nonphysiological muscle contractions, and in some cases “tic-like” muscle contractions are observed. Although both anterior and posterior nonpositional FSI exist, the anterior direction can be observed more commonly, especially in patients with controllable nonpositional FSI.

An important factor in FSI is the burden and perception of disease. Patients with controllable positional or nonpositional FSI often do not have any symptoms and therefore do not interpret their “condition” as pathologic but rather as an enhanced ability. Therefore, it is likely that many patients with controllable FSI do not even seek medical attention, which is also the reason why patients with controllable FSI are surely underrepresented in many studies.

The perception of this form of FSI can vary extensively. It ranges from the positive interpretation as delightful party trick maneuver to the negative interpretation as attention-seeking behavior.

In contrast, patients with noncontrollable positional or nonpositional FSI often carry a large burden of disease in terms of severe loss of function, discomfort, and pain.

The presumed cause for positional as well as nonpositional FSI is an imbalance of muscle activation patterns. In the group of patients with positional FSI, hypoactivity of certain rotator cuff muscles appears to lead to excessive translation of the humeral head during movement of the arm. Although hypoactivity of the infraspinatus muscle as well as the teres minor muscle can result in posterior instability, hypoactivity of the subscapularis muscle seems to lead to anterior instability. This can, for example, explain why the wall-slide maneuver (resisted external rotation during arm elevation) stabilizes the shoulder in patients with positional posterior FSI.

Non-positional FSI appears to be caused by hyperactivity of larger muscles, which pull the humeral head out of its physiological position. For example, anterior or anteroinferior non-positional FSI seems to be caused by excessive contraction of the pars abdominalis of the pectoralis major muscle, while possibly overactive large internal rotators such as the latissimus dorsi muscle and teres major muscle cause posterior or posteroinferior instability of the humeral head.

Few principles that have provided treatment success in the past ought to be mentioned.

First of all, patients with controllable FSI should neither be treated surgically nor conservatively as they have not lost control over the stability of their shoulders and are unlikely to develop any secondary degenerative changes.

Patients with noncontrollable FSI should not undergo surgical treatment, because of the unpredictable outcome.

As the pathology might be self-limiting and disappear over the course of several years, skillful neglect has been proposed as a treatment alternative. However, this long-term approach with unguaranteed outcome is hardly accepted by the often young patients who want and need to regain function quickly.

?It is key to provide a targeted conservative treatment including core stabilization, coordination exercises, strengthening, and biofeedback.