Abnormal posturing

Abnormal posturing describes involuntary contraction or extension of an arm or leg. It's a medical emergency and immediate hospital care is required even if the patient is otherwise conscious and responsive. It's a sign of severe brain damage. It's caused when one of a pair of complementary muscles (such as the biceps and triceps) is incapacitated, the other is working normally, but is contracted by a stimulus, typically pain.
As the severity of abnormal posturing is an accurate indicator of the level of brain damage, posturing is part of the assessment of a patient under the Glasgow Coma Scale. In patients with otherwise similar injuries, abnormal posturing usually indicates a worse prognosis.
Although trauma to the brain is a typical cause, it can also be caused by a stroke, intracranial hemorrhage, brain tumor, and encephalopathy. The presentation of posturing can be helpful in a diagnosis. For example, posturing on only one side is a good indication of stroke.
Abnormal posturing at Wikipedia