23.16 The reinforcing ligamentous structures

• The gleno-humeral capsulo-ligamentous structures are lax but solid to allow a large degree of movement

• Ligaments are relaxed in the neutral position (arm alongside the body)

• Ligaments tighten in external rotation

• Helocoidal tightening in external rotation + abduction

• Ligaments restrain in three ways

  • Limitation of rotation (axial and shearing) forces

  • Limitation of perpidicular displacement from the glenoid (axial tension in ligaments)

  • Limitation of displacement parallel to the glenoid (shearing forces) where they act as a mechanical block

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