Shoulder instability is defined as the inability to maintain the humeral head at the center of the glenoid during activearm mobilization.
Shoulder instability has to be classified into several parameters in order to be characterized. Clinical history should define the existence of a traumatic episode, the energy involved in that episode, the presence of a concomitant hypermobility (elasticity) and the evolutionary character of instability and consequently of symptomatology.
Repeated injuries can lead to progressive structural changes (capsule labrum and ligaments), which is called acquired instability. These patients have a clinical history, with several factors that contribute to the onset of instability, such as an underlying condition of joint hypermobility and a sports activity that favors the onset of progressive overload.
Besides the origin of the instability, it must be characterized according to the degree of instability. This may be very small and give only discomfort and easy tiredness, may be of intermediate degree and in addition to these complaints give pains by inflammation of the tendons and sensations that the shoulder is sometimes “not in place” or the highest degree that corresponds to shoulder dislocation episodes.
The direction of instability may be difficult to determine either by clinical history or by objective examination. Sometimes there is a need foradditional examinations to target the typical structural injuries of the various directions of instability. Anterior instability is the most frequent, with an incidence greater than 95%.
According to what we have said so far, instability / dislocation must be classified (characterized) in several ways:
- By its origin – Traumatic (single or repetitive injuries) and atraumatic
- By its direction – Unidirectional (forward, backward, downward), Bidirectional and Multidirectional
- By its degree – Minor, Recurrent dislocation
Thus someone who after a violent trauma becomes shoulder dislocations has unidirectional traumatic instability (95% ofcases forward) of the shoulder. On the other hand someone who through minor injuries has been doing minor ligament injuries will have minor shoulder instability with one, two or more directions of instability and no shoulder dislocations but the humeral head is not in the center of the glenoid during arm mobilization. which leads to pain and inability to perform certain gestures.
How it all happens
The glenohumeral (shoulder) joint due to its potential mobility is intrinsically unstable. The stabilizing elements areclassically divided into static (bones and ligaments) and dynamic (tendons and muscles that make them work).
Labrum is a fibro-cartilage consisting of confluence of ligaments and capsular insertion in the anteriorrim of the glenoid. Itsessential functions are increasing the depth of the glenoid and increasing the contact surface with the humeral head.
The joint capsule is reinforced by three glenohumeral ligaments (upper, middle and lower).
We know that ligament failure occurs most often at the level of the glenoid insertion and is accompanied by plastic deformationof the body of the ligament complex prior to the failure of the glenoid insertion.
This fact suggests that repeated trauma can cause distension and consequent laxity of this stabilizing element that is fundamental for shoulder biomechanics.
Shoulder muscle strengths are defined by their power and direction, which can be broken down into two elements:
compressive forces and translational forces. If the former stabilize the joint, the others may unsettle the joint.
We may then have shoulder instability only by changes in muscle power and coordination, or by injuries to the labrum, ligaments, and joint capsule due to single and / or repeated injuries. In addition to these changes, certain characteristics of the patient with hypermobility (greater elasticity) may contribute to instability.
Clinical history (as dislocations followed) is critical in beginning to characterize instability.
The clinical examination is based mainly on the verification of risk factors such as joint hypermobility, alteration of the scapulo-thoracic rhythm, and the verification of signs of instability. These are mainly characterized by apprehension (fear) that the patient expresses in certain shoulder positions and not by painful tests.
Radiographic examinations may, due to erosion of the anterior rim of the glenoid and the existence of injury to the posterior face of the humeral head, give indirect signs of the direction and degree of instability.
Classical Computed Axial Tomography is of very little interest but can be used to quantify bone loss.
Magnetic resonance imaging should be used to screen for lesions of the labrum and capsular ligaments in patients without episodes ofdislocation, or in those where the direction of dislocation cannot be clinically defined.
In cases of recurrent shoulder dislocation (more than 1 episode), surgical treatment is the only solution. The introduction of arthroscopic techniques for the treatment of these patients does not require the use of magnetic resonance imaging to characterize ligament injuries.
This is advantageously performed during the intervention through clinical observation under anesthesia and visualization and direct testing of the lesions.
After the first episode of traumatic dislocation, it is classic to perform immobilization of the shoulder in adduction and internal rotation (arm to chest) for aperiod of three weeks. However studies with a high degree of evidence show an equal incidence of new episodes of dislocation in patients who have not been immobilized. Thus, keeping the arm at chest relative rest during the period of discomfort is enough. There is usually no need to take medication, but if there is pain, an anti-allergic and / or anti-inflammatory may be taken. After 3 weeks you should start a physical therapy program.
Another recent approach to traumatic instability is the surgical repair of ligament injuries at the first episode of dislocation.
This action aims mainly to prevent the progressive degradation of the capsulo-ligament complex with future episodes of dislocation.Recentarthroscopic techniques allow the indication for intervention for the first episode of dislocation in athletes under 30 years of age.
Treatment of recurrent shoulder dislocation is surgical. Studies have shown a higher rate of new episodes the youngerthe patient is and we know that the number of dislocations aggravates capsular-ligament complex injuries and therefore the outcome of treatment.
Conservative (non-surgical) treatment, however, can be viewed as a transient form of management of the clinical situation, such as during the sporting season or the school periods.
For the surgical approach of shoulder instability, it is essential to study all the characteristics of instability, to know thepatient’s sports activity , to know which injuries result from instability: bone, ligament and capsular, in order to decide which techniques to use. The goal is to reconstruct the anatomy. As we have seen, the use of arthroscopy allows the surgeon to observe all quadrants of the shoulder without opening it, testing it under visualization and adopting treatment to the needs of each patient, deciding which techniques to use under direct vision of the shoulder to be treated. So if there is a lesion of the labrum it can be reinserted, if there is a distension (enlargement) of the capsule it can be plied (folded).
Arthroscopy is not yet able to repair bone lesions in cases where it is greater than 25% of the glenoid surface. In thesecases open interventions with transfer and fixation of bone grafts, classically of the coracoid (shoulder bone eminence ) are indicated.
The incidence of relapses is higher in arthroscopic stabilization compared with open surgery (2-18% to 11%). However, arthroscopic procedures are associated with less loss of mobility and function of the shoulder joint, thus maintaining the sportive gesture.
Conservative (non-surgical) treatment is the method of choice for non-traumatic instability and acquired instability. The intervention aims to increase the compression of the humeral head in the glenoid and to restore the scapulo-thoracic rhythm. Most authors recognize the importance of strengthening exercises for the rotator cuffs (tendons that involve the shoulder joint) and the deltoid (outside arm muscle) as a way to control glenohumeral translation.
Exercises that require coordination between various muscle groups should be used to reprogram normal patterns ofmuscle activity.
Points to Retain
There are several forms, degrees and directions of instability, the most severe being shoulder dislocation.
Non-traumatic instabilities are treated with physiotherapy and surgical treatment is performed only in resistant cases. Traumatic instabilities are most often treated surgically.
After the dislocation episode it is sufficient to use a brachial suspension for rest.
In some cases, the patient may benefit from having the first episode of dislocation. Arthroscopy gives a direct view of the lesions, a very accurate approach to all quadrants of the shoulder, and anatomical repairof the lesions.