Which is true regarding shoulder dislocation -

The features of posterior dislocation of the shoulder are not very striking, and for that reason the injury is often overlooked. An important sign is fixed medial (internal) rotation of the arm, which cannot be rotated outward (externally), even to neutral position. Radiography may be misleading if only the ordinary anteroposterior film is available, because the dislocation may not be apparent or at least not obvious on this projection.