Spinal cord injury

A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. Symptoms may include loss of muscle function, sensation, or autonomic function in the parts of the body served by the spinal cord below the level of the injury. Injury can occur at any level of the spinal cord and can be complete injury, with a total loss of sensation and muscle function, or incomplete, meaning some nervous signals are able to travel past the injured area of the cord. Depending on the location and severity of damage, the symptoms vary, from numbness to paralysis to incontinence. Long term outcomes also ranges widely, from full recovery to permanent tetraplegia (also called quadriplegia) or paraplegia. Complications can include muscle atrophy, pressure sores, infections, and breathing problems. In the majority of cases the damage results from physical trauma such as car accidents, gunshots, falls, or sports injuries, but it can also result from nontraumatic causes such as infection, insufficient blood flow, and tumors. Just over half of injuries affect the cervical spine, while 15% occur in each of the thoracic spine, border between the thoracic and lumbar spine, and lumbar spine alone. Diagnosis is typically based on symptoms and medical imaging. Efforts to prevent SCI include individual measures such as using safety equipment, societal measures such as safety regulations in sports and traffic, and improvements to equipment. Treatment starts with restricting further motion of the spine and maintaining adequate blood pressure. Corticosteroids have not been found to be useful. Other interventions vary depending on the location and extent of the injury, from bed rest to surgery. In many cases, spinal cord injuries require long-term physical and occupational therapy, especially if it interferes with activities of daily living. In the United States, about 12,000 people a year survive a spinal cord injury. The most commonly affected group are young adult males. SCI has seen great improvements in its care since the middle of the 20th century. Research into potential treatments includes stem cell implantation, engineered materials for tissue support, epidural spinal stimulation, and wearable robotic exoskeletons. Spinal cord injury can be traumatic or nontraumatic, and can be classified into three types based on cause: mechanical forces, toxic, and ischemic (from lack of blood flow). The damage can also be divided into primary and secondary injury: the cell death that occurs immediately in the original injury, and biochemical cascades that are initiated by the original insult and cause further tissue damage. These secondary injury pathways include the ischemic cascade, inflammation, swelling, cell suicide, and neurotransmitter imbalances. They can take place for minutes or weeks following the injury. At each level of the spinal column, spinal nerves branch off from either side of the spinal cord and exit between a pair of vertebrae, to innervate a specific part of the body. The area of skin innervated by a specific spinal nerve is called a dermatome, and the group of muscles innervated by a single spinal nerve is called a myotome. The part of the spinal cord that was damaged corresponds to the spinal nerves at that level and below. Injuries can be cervical 1–8 (C1–C8), thoracic 1–12 (T1–T12), lumbar 1–5 (L1–L5), or sacral (S1–S5). A person's level of injury is defined as the lowest level of full sensation and function. Paraplegia occurs when the legs are affected by the spinal cord damage (in thoracic, lumbar, or sacral injuries), and tetraplegia occurs when all four limbs are affected (cervical damage). SCI is also classified by the degree of impairment. The International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), published by the American Spinal Injury Association (ASIA), is widely used to document sensory and motor impairments following SCI. It is based on neurological responses, touch and pinprick sensations tested in each dermatome, and strength of the muscles that control key motions on both sides of the body. Muscle strength is scored on a scale of 0–5 according to the table on the right, and sensation is graded on a scale of 0–2: 0 is no sensation, 1 is altered or decreased sensation, and 2 is full sensation. Each side of the body is graded independently. In a 'complete' spinal injury, all functions below the injured area are lost, whether or not the spinal cord is severed. An 'incomplete' spinal cord injury involves preservation of motor or sensory function below the level of injury in the spinal cord. To be classed as incomplete, there must be some preservation of sensation or motion in the areas innervated by S4 to S5, e.g. voluntary external anal sphincter contraction. The nerves in this area are connected to the very lowest region of the spinal cord, and retaining sensation and function in these parts of the body indicates that the spinal cord is only partially damaged. Incomplete injury by definition includes a phenomenon known as sacral sparing: some degree of sensation is preserved in the sacral dermatomes, even though sensation may be more impaired in other, higher dermatomes below the level of the lesion. Sacral sparing has been attributed to the fact that the sacral spinal pathways are not as likely as the other spinal pathways to become compressed after injury due to the lamination of fibers within the spinal cord.