Shoulder:Glenohumeral Instability/Posterior Instability

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Bullet Points

  • Posterior shoulder instability is not as rare as previously though.


  • Diagnosing posterior instability may be difficult because patients often report vague symptoms not linked to a clear history of traumatic shoulder dislocation.


  • This condition is consequently often misdiagnosed or patients experience a delay in diagnosis.


  • It that encompasses different acute and chronic pathologies involving the labrum, the cartilage, the capsule, bony lesions.


  • A tear between the posterior labrum and the glenoid cartilage without complete detachment of the labrum is described as a Kim lesion. It is postulated that this lesion is due to posterior force acting on the posterior-inferior glenohumeral ligament as it attaches to the posterior labrum.


  • Numerous classifications exit, none having done unanimity.


  • Risk factors for recurrent instability are: (1) age below 40 at time of first instability; (2) dislocation during a seizure; (3) a large reverse Malgaigne (Hill-Sachs) lesion; (4) glenoid retroversion, and (5) a high and horizontally oriented acromion in the sagittal plan.


  • Hyperlaxity is multidirectional but instability is almost exclusively unidirectional.


  • Physical examination comprises the articular range of motion, the rotator cuff, and jerk, Kim and O’Brien tests.


  • Three views plain radiographs, including true anteroposterior of the glenohumeral joint, scapular Y (scapular lateral), and Bernageau views are the mainstay of imaging in the setting of shoulder instability.


  • An internally rotated humeral head gives a rounded appearance on anteroposterior view, which is called the lightbulb sign.


  • In case of a suspicion about posterior dislocation of the shoulder, additional imaging including, depending of the type of instability, magnetic resonance arthrography (MRA) or computed tomography (CT) is required.


  • Acute or recurrent posterior dislocations can be treated conservatively, by soft tissue or bony procedures.


  • Surgical options include anatomic reconstruction as well as non-anatomic procedures such as subscapularis tendon transfer, allo-/autograft reconstruction, derotation osteotomy or shoulder arthroplasty.


  • Treatment of locked dislocation depends on the extent of the articular defect size of the humeral head, duration of the dislocation and patient-specific conditions such as age and activity levels.


Key words

Posterior shoulder stabilization; Functional instability; Soft tissue injuries; Locked dislocation; Subluxation; Epidemiology; Labrum; ABC classification; Treatment options; Arthroscopy; McLaughlin procedure; Bone block; Clinical outcomes; Complications.


History

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Anecdote

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Epidemiology and Mechanism

Posterior dislocation of the shoulder accounts for around 20% of all shoulder dislocations, which is much higher than the 4-5% prevalence previously mentioned in the literature.[1] A reason for this large discrepancy is the challenge of clinical diagnosis, since symptoms are often subtle and patients often lack the typical feeling of posterior apprehension in provocative arm positions.


Anatomy, Pathoanatomy

Soft Tissue Lesion

Four different type of labral insertion have been described by Nourissat et al.[2] Type 1, 60% of the cases, correspond to a posterior labrum totally inserted in the glenoid, with direct contact with the cartilage, totally flush. In type 2 (20% of the cases), insertion of the superior segment is medialized. Type 3, 15% of the cases, represents an associated medialization of the superior and medial segment of the posterior labrum. Type 4 is a medialized insertion of the all-posterior labrum.




Consequently, a subchondral cleft (labrum and capsule attached but no tear) may be a normal finding.[3] Surgeons should be aware that while anterior capsule anatomy is quite variable, the posterior capsular insertion tends to be more homogenous in appearance among patients (Figure).

A) Normal insertion of the posterior capsule. B) Posterior disinsertion of the capsule.







Reverse humeral avulsion of the glenohumeral ligaments (rHAGL)

Posterior arthroscopic view of a left shoulder. Observe the humeral avulsion of the capsule.

References

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  1. ↑ Song DJ, Cook JB, Krul KP, Bottoni CR, Rowles DJ, Shaha SH, Tokish JM. High frequency of posterior and combined shoulder instability in young active patients. J Shoulder Elbow Surg. 2015 Feb;24(2):186-90. doi: 10.1016/j.jse.2014.06.053
  2. ↑ Nourissat G, Radier C, Aim F, Lacoste S. Arthroscopic classification of posterior labrum glenoid insertion. Orthop Traumatol Surg Res. 2014 Apr;100(2):167-70. doi: 10.1016/j.otsr.2013.09.015
  3. ↑ Campbell SE, Dewitt RM, Cameron KL, Thompson AK, Owens BD. Posterior chondrolabral cleft: clinical significance and associations with shoulder instability. HSS J. 2014;10:208-212. doi: 10.1007/s11420-014-9404-x
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