Horner's syndrome after cervical fusion

My grandmother has got Horner's syndrome after cervical fusion. What does it mean? Thank you

Horner syndrome is an uncommon disorder. It caused by damage to sympathetic nerves to the face and eye, so I suppose that something went wrong during her cervical fusion. Other reasons that it happens are: stroke, tumor in the upper part of the lung and low cervical spinal cord, cluster headaches or injury to a carotid artery in the neck. As I know there’s no specific treatment for Horner syndrome.