TRAUMA 2023, Jan, 22 | 12:00 am

POSTERIOR GLENOHUMERAL DISLOCATION

POSTERIOR GLENOHUMERAL DISLOCATION

Incidence

  • These injuries represent 2% to 4% of shoulder dislocations and 2% of shoulder injuries.
  • They are often unrecognized by primary care and emergency physicians, with 60% to 80% missed on initial examination.

Mechanism of Injury

  • Indirect trauma: This is the most common mechanism.
    • The shoulder typically is in the position of adduction, flexion, and internal rotation.
    • Electric shock or convulsive mechanisms may produce posterior dislocations owing to the greater muscular force of the internal rotators (latissimus dorsi, pectoralis major, and subscapularis muscles) compared with the external rotators of the shoulder (infraspinatus and teres minor muscles).
  • Direct trauma: This results from force application to the anterior shoulder, resulting in posterior translation of the humeral head.

Clinical Evaluation

  • Clinically, a posterior glenohumeral dislocation does not present with striking deformity; the injured upper extremity is typically held in the traditional sling position of shoulder internal rotation and adduction. These injuries may be missed if a complete radiographic series is not obtained.
  • A careful neurovascular examination is important to rule out axillary nerve injury, although it is much less common than with anterior glenohumeral dislocation.
  • On examination, limited external rotation (often <0 degrees) and limited anterior forward elevation (often <90 degrees) may be appreciated.
  • A palpable mass posterior to the shoulder, flattening of the anterior shoulder, and coracoid prominence may be observed.

Radiographic Evaluation

  • Trauma series of the affected shoulder: AP, scapular-Y, and axillary views. A Velpeau axillary view (see earlier) may be obtained if the patient is unable to position the shoulder for a standard

axillary view.

  • On a standard AP view of the shoulder, signs suggestive of a posterior glenohumeral dislocation include:
    • Absence of the normal elliptic overlap of the humeral head on the glenoid.
    • Vacant glenoid sign: The glenoid appears partially vacant (space between anterior rim and humeral head >6 mm).
    • Trough sign: impaction fracture of the anterior humeral head caused by the posterior rim of

glenoid (reverse Hill-Sachs lesion). This is reported to be present in 75% of cases.

    • Loss of profile of humeral neck: The humerus is in full internal rotation.
    • Void in the superior/inferior glenoid fossa, owing to infero-superior displacement of the dislocated humeral head.
  • Glenohumeral dislocations are most readily recognized on the axillary view; this view may also

demonstrate the reverse Hill-Sachs defect.

  • Computed tomography scans are valuable in assessing the percentage of the humeral head involved with an impaction fracture.

Classification

Etiologic Classification

Traumatic: Sprain, subluxation, dislocation, recurrent, fixed (unreduced)

Atraumatic: Voluntary, congenital, acquired (due to repeated microtrauma)

Anatomic Classification

Subacromial (98%): Articular surface directed posteriorly with no gross displacement of the humeral head as in anterior dislocation; lesser tuberosity typically occupies glenoid fossa; often associated with an impaction fracture on the anterior humeral head

Subglenoid (very rare): Humeral head posterior and inferior to the glenoid

Subspinous (very rare): Humeral head medial to the acromion and inferior to the spine of the scapula

 

Treatment

Nonoperative

  • Closed reduction requires full muscle relaxation, sedation, and analgesia.
    • The pain from an acute, traumatic posterior glenohumeral dislocation is usually greater than with an anterior dislocation and may require general anesthesia for reduction.
    • With the patient supine, traction should be applied to the adducted arm in the line of deformity

with gentle lifting of the humeral head into the glenoid fossa.

    • The shoulder should not be forced into external rotation, because this may result in a humeral

head fracture if an impaction fracture is locked on the posterior glenoid rim.

    • If prereduction radiographs demonstrate an impaction fracture locked on the glenoid rim, axial traction should be accompanied by lateral traction on the upper arm to unlock the humeral head.
  • Postreduction care should consist of a sling and swathe if the shoulder is stable. If the shoulder

subluxes or redislocates in the sling and swathe, one should consider surgical stabilization.

    • With a large anteromedial head defect, better stability may be achieved with immobilization in external rotation.
    • External rotation and deltoid isometric exercises may be performed during the period of

immobilization.

    • After discontinuation of immobilization, an aggressive internal and external rotator strengthening program is instituted.

Operative

  • Indications for surgery include:
    • Major displacement of an associated lesser tuberosity fracture
    • A large posterior glenoid fragment
    • Irreducible dislocation or an impaction fracture on the posterior glenoid preventing reduction
    • Open dislocation
    • An anteromedial humeral impaction fracture (reverse Hill-Sachs lesion)
    • Twenty percent to 40% humeral head involvement: transfer the lesser tuberosity with attached subscapularis into the defect (modified McLaughlin procedure)
    • Greater than 40% humeral head involvement: hemiarthroplasty with neutral version of the

prosthesis

    • Recurrent instability
  • Surgical options include open reduction, infraspinatus muscle/tendon plication (reverse Putti-Platt procedure), long head of the biceps tendon transfer to the posterior glenoid margin (Boyd-Sisk procedure), humeral and glenoid osteotomies, and capsulorrhaphy.
  • Voluntary dislocators should be treated nonoperatively, with counseling and strengthening exercises.

Complications

  • Fractures: These include fractures of the posterior glenoid rim, humeral shaft, lesser and greater tuberosities, and humeral head.
  • Recurrent dislocation: The incidence is increased with atraumatic posterior glenohumeral dislocations, large anteromedial humeral head defects resulting from impaction fractures on the glenoid rim, and large posterior glenoid rim fractures. They may require surgical stabilization to prevent recurrence.
  • Neurovascular injury: This is much less common in posterior versus anterior dislocation, but it may include injury to the axillary nerve as it exits the quadrangular space or to the nerve to the

infraspinatus (branch of the suprascapular nerve) as it traverses the spinoglenoid notch.

  • Anterior subluxation: This may result from “overtightening” posterior structures, forcing the humeral head anteriorly. It may cause limited flexion, adduction, and internal rotation.