The role of head trauma in the subsequent development of Alzheimer's disease is undergoing intense study. It is likely that serious head injuries shorten the period before Alzheimer's disease would otherwise have developed. There may be a link between traumatic brain injury and the development of Alzheimer’s Disease years later.

In 1999 the American Academy of Neurology's position was that trauma and/or head injury is unlikely to create or permanently aggravate multiple sclerosis. This conclusion is not universally accepted among neurologists and research continues to suggest a possible link.

Parkinsonian patients injured in car accidents, including head injury, suffer a temporary aggravation of their symptoms. There does not seem to be a significant risk of permanent exacerbation of Parkinson's disease from a single head injury, but research continues. Repeated blows to the head, as in boxing, do pose a risk of causing Parkinson's disease.

There are many case reports of mental illness, including obsessive compulsive disorder, depression, mania, hallucinations, etc., following head injuries. Depending on the location and severity of the brain damage, preexisting mental illness may be magnified by a brain injury.

Serious frontal lobe injury can cloud judgment and decrease societal inhibitions, making drug and alcohol addiction a significant risk. Those with pre-existing addictions are at greatest risk.

Studies confirm that persons who have suffered from previous brain injuries are more susceptible to reinjury of the brain after a new trauma.

The minimum force necessary to damage the brain is still unknown. Depending on each person's individual susceptibility to brain injury, the threshold may vary considerably among individuals. While engineers and accident reconstructionists can estimate the forces involved in the accident by viewing the speed of, and the damage to, the vehicles involved, the best judges of permanent damage are the health care providers caring for the patient.

Cases of serious brain injury inevitability raise the essential issue of long term or permanent care. Rehabilitation specialists examine such patients and extrapolate their medical and non-medical needs for the remainder of their life span. Non-medical needs include home modification, wage loss, home care, and transportation needs.

The spinal cord extends downward from the brain and travels down the back in a bony tunnel, protected on all sides by the vertebral bodies and the bony lamina extending from those vertebral bodies. In some people, the bony tunnel is rather narrow, leaving just enough room for the spinal cord to function but no room for any mishaps.

Everyone is familiar with paralysis resulting from diving into a shallow pool. When the victim's face or chin hits the floor of the swimming pool, the head is snapped back. This acute hyperextension causes ligaments (ligaments hold bones together) running along the inner walls of the cervical spinal canal to buckle and acutely bang the spinal cord. If the patient is lucky, the spinal cord is only stunned, and will recover in a day or two. If he's not, the cord will never recover and the patient will be left weak or completely paralyzed in the arms and legs, sometimes just the legs.

Hyperextension injuries to the cervical spinal cord can also result from football players spearing another player or from falling on their face the wrong way.