Shoulder instability and dislocation – Definition:
Shoulder instability is a pathology that causes specific symptoms (anxiety, catching, cracking, pain, dislocation) that originates in partial or total loss of normal anatomic interfacing between the humeral head and the scapula’s glenoid; in the first instance, the term used is subluxation, in the second one, dislocation of the gleno-humeral joint.
The best known form of shoulder instability is acute instability by antero-internal gleno-humeral dislocation of the shoulder (shoulder dislocation). When it doesn’t heal properly, this form of dislocation can result in chronic instability with recurrent anterior dislocation or subluxation. The surgeon refers to this as anterior shoulder instability in the form of recurrent dislocation.
In this anterior shoulder instability pathology, two main types of shoulder stabilization surgery are possible:
- stabilization through anterior and posterior capsulo-ligamentous repair surgery, known as arthroscopic bipolar fixation
- stabilization through reinforcement surgery using a bone block which very often comes from the coracoid process; this procedure is known as arthroscopic Latarjet procedure.
Video of arthroscopic shoulder stabilization surgery procedures:
Anatomy of shoulder stability and instability:
Three main factors contribute to shoulder stability:
- bone structures: the volume of the humeral head is markedly greater than that of the glenoid, which in contrast with other joints such as the hip, contributes greatly to make the shoulder instable.
- capsulo-ligamentous and labral structures: to keep these osseous parts together and increase their contact surface, the glenoid has a fibrous extension that looks like a meniscus and is called the labrum. There is also a capsulo-ligamentous layer, like a hammock (rope interweave) linking the glenoid to the humerus.
- cuff muscles: as stabilizers they are less important than the capsulo-ligamentous structures, but the plasticity of muscles is an advantage as these can be strengthened to stabilize the shoulder; they must be preserved as much as possible in stabilization surgery, which makes arthroscopy all the more preferrable.
With these 3 main factors defined, one understands that any acquired pathology (congenital or genetic) of one of these 3 structures will increase the risk of instability (shoulder dislocation): bone malformation, muscular anomalies, ligamentous anomalies such as ligamentous hyperlaxity.
In a first-episode anterior shoulder dislocation, capsulo-ligamentous lesions systematically occur, which can never heal completely:
- tear of the labrum and anterior capsulo-ligamentous tear, which consists in detachment of the anteroinferior gleno-humeral ligaments associated with a lesion of the anteroinferior labrum (Bankart lesion)
- posterior capsular lesion, in an anterior dislocation, at the site where it is attached to the humerus, the posterior capsule ends up holding the humeral head at the front, so there is posterior capsule distension at the humerus.
These systematic lesions can be associated with other frequent lesions:
- SLAP lesion, which refers to an antero-inferior labral tear extending to the superior labrum and biceps;
- fracture and cartilaginous lesion of the glenoid; in shoulder dislocation, the lesion of the labrum can be associated to a lesion of the glenoid (glenoid fracture or Bony Bankart; cartilaginous or GLAD lesion);
- the posterior capsular lesion can extend to the posterior humerus, which is referred to as posterior humeral notch (Hill-Sachs lesion or Malgaigne notch)
The examination that provides the most accurate diagnosis for these instability lesions is CT arthrography of the shoulder.
Depending on the instability lesions found, on the frequency of the dislocations and on the type of sports practised, two main types of shoulder stabilization surgery can be performed:
- repair surgery by anterior and posterior capsulo-ligamentous plication, Bankart procedure + remplissage, called arthroscopic bipolar fixation
- stabilization through reinforcement surgery using a bone block which very often comes from the coracoid process, this procedure is known as arthroscopic Latarjet procedure.