Shoulder dislocation

Shoulder Dislocation Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Jumana Nagarwala, M.D., Senior Staff Physician, Department of Emergency Medicine, Henry Ford Hospital; Cafer Zorkun, M.D., Ph.D. [2]

Pathophysiology

Associated Conditions

• • Hill-Sach lesions (describes a characteristic defect of the posterolateral surface of the humeral head, and represents a compression fracture)
  • Labral lesions (i.e., Bankart lesion)
  • Bony glenoid lesions - Osseous anterior glenoid rim fractures (44%), bony Bankart lesions, fracture of the greater tuberosity
  • Intraarticular loose body
  • Rotator cuff lesions - Supraspinatus tears or subscapularis tears

Diagnosis

X Ray

• Posterior dislocation may be missed initially on frontal radiographs in 50% of cases.
• Signs on frontal radiographs are subtle, including the trough line sign and the loss of normal "half-moon overlap".
• Axillary, scapular Y, or posterior oblique projections are needed for confirmation.
• The absence of external rotation on images in a standard shoulder series is a clue to posterior dislocation.
• Loss of half-moon overlap: On a normal true anteroposterior image, there is a half-moon overlap between the humeral head and the glenoid. In a posteriorly dislocated shoulder, there is lateral displacement of the humeral head with respect to the glenoid (losing the half-moon overlap)
• Trough line sign: In posterior dislocation, the anterior aspect of the humeral head becomes impacted against the posterior glenoid rim. With sufficient force, this causes a compression fracture on the anterior aspect of the humeral head. This compression fracture is analogous to the Hill-Sachs compression fracture seen with anterior dislocation of the glenohumeral joint. Frontal radiographs reveal two nearly parallel lines in the superomedial aspect of the humeral head.

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Shown below are the X ray findings of posterior shoulder dislocation.

Courtesy: RadsWiki, copyleft source

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Shown below are the X ray findings of anterior shoulder dislocation.

Courtesy: RadsWiki, copyleft source

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Shown below are the X ray findings of anterior shoulder dislocation post reduction.

Courtesy: RadsWiki, copyleft source

References

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