Shoulder instability and dislocation – Definition
Shoulder dislocation is a frequent sports injury; it is the main joint of the shoulder coming apart between the humeral head and the scapula's glenoid. Shoulder dislocation is sometimes confused with acromioclavicular dislocation.
Acromioclavicular dislocation is typically the result of a fall on the point of the shoulder while the trauma from which anterior shoulder dislocation results is most of the time a direct fall onto the hand.
In the typical sporting dislocation, the shoulder is displaced frontally in a fall where the arm is stretched backward. while running (basketball, football), from height (horseriding, cycling), at high speed (ski). Shoulder dislocation can also result from contact (rugby), or resistance to a throw whilst in the cocking position, as in handball or basketball.
The first episode of dislocation justifies relocation by external manoeuvre (after x-ray confirming absence of fracture) and brief shoulder immobilization, for approx. 10 days. Shoulder surgery is seldom necessary after the 1st episode but specialized shoulder rehabilitation must be started very quickly.
Video of arthroscopic shoulder stabilization surgery
Anatomy of shoulder stability and instability
Three main natural 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 shoulder instability.
- labrum and capsulo-ligamentous 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: it is the shoulder’s articular capsule.
- tendons and muscles of the rotator cuff: 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.
Whoever appreciates the importance of these three stabilizing structures of the shoulder understands that any acquired pathology (congenital, genetic) of one of these three elements will increase the risk of instability (shoulder dislocation), bone deformity, muscular anomalies, ligamentous anomalies such as constitutional ligamentous hyperlaxity or shoulder hyperlaxity.
In a first-episode anterior shoulder dislocation, capsulo-ligamentous lesions systematically occur, which can never heal completely:
- labral tear and anterior capsulo-ligamentous tear, consisting 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 ligamentous and capsular (labrum) lesions which are always found after a first dislocation episode can also be associated with other instability lesions which are not systematic but frequent:
- 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 aka GLAD lesion)
- the posterior capsular lesion can spread to the posterior humerus, which is referred to as posterior humeral notch (Hill-Sachs lesion or Malgaigne notch)
The diagnostic examination that offers the most accuracy for these dislocation and instability lesions is called CT arthrography; MRI arthrography is an alternative in case of allergy to iodine.
Rehabilitation of shoulder dislocation in sports:
Specific rehabilitation must begin as soon as initial shoulder pain allow it, that is to say 10 days after dislocation approximately. Rehabilitation of a dislocated shoulder first consists in reducing pain (pain control physiotherapy), and restoring range of motion.
The second stage will focus on strengthening the stabilizing muscles of the shoulder (rotators) so as to compensate for the systematic instability lesions that occurred.
Finally, rehabilitation will address proprioception to optimize sensation and articular feel. This rehabilitation work is essential and it is the best method to prevent recurrent shoulder dislocations and painful instability.
Principle of surgical treatment of the unstable shoulder-dislocation
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 recurring anterior dislocation or subluxation. This is known as anterior shoulder instability in the form of recurrent dislocation.
Rehabilitation is the best way to prevent the shoulder instability pathology. Unfortunately, despite well managed rehabilitation, recurrent instability can persist, in which case arthroscopic shoulder stabilization surgery must be performed.
In anterior instability, two main shoulder surgery procedures are possible:
- stabilization through anterior and posterior capsulo-ligamentous repair surgery, known as 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.
Arthroscopic Latarjet is the surgery of choice to treat an unstable shoulder in a young patient who practises contact sports, judo, handball, rugby.