damage to the accessory nerve would result in
Accessory nerve disorder Injury to the spinal accessory nerve can cause an accessory nerve disorder or spinal accessory nerve palsy, which results in diminished or absent function of the sternocleidomastoid muscle and upper portion of the trapezius muscle.
Dead arm syndrome The shoulder is unstable and dislocation may come next. Dead arm syndrome will not go away on its own with restâ€”it must be treated. If there is a SLAP lesion, then surgery is needed to repair the problem. If the injury is caught before a SLAP tear, then physical therapy with stretching and exercise can restore it.