eMedicine Specialties > Physical Medicine and Rehabilitation > Spinal Cord Injury

Spinal Cord Injury - Definition, Epidemiology, Pathophysiology

Author: Segun T Dawodu, MD, JD, MBA, FAAPMR, FAANEM, CIME, DipMI(RCSed), Former Clinical Instructor, Mount Sinai Medical School; Current Director, Pain and Injuries Rehabilitation Services, PMRehab Pain and Sports Medicine Associates
Contributor Information and Disclosures

Updated: Mar 30, 2009

Definitions and Pathophysiology

Spinal cord injury (SCI) is an insult to the spinal cord resulting in a change, either temporary or permanent, in its normal motor, sensory, or autonomic function. The International Standards for Neurological and Functional Classification of Spinal Cord Injury is a widely accepted system describing the level and extent of injury based on a systematic motor and sensory examination of neurologic function.^1,2 The following terminology has developed around the classification of SCI:

• Tetraplegia (replaces the term quadriplegia) - Injury to the spinal cord in the cervical region, with associated loss of muscle strength in all 4 extremities
• Paraplegia - Injury in the spinal cord in the thoracic, lumbar, or sacral segments, including the cauda equina and conus medullaris

SCI can be sustained through different mechanisms, with the following 3 common abnormalities leading to tissue damage:

• Destruction from direct trauma
• Compression by bone fragments, hematoma, or disk material
• Ischemia from damage or impingement on the spinal arteries

Edema could ensue subsequent to any of these types of damage. The different clinical presentations of the above causes of tissue damage are explained further below.

Spinal shock

Spinal shock is a state of transient physiologic (rather than anatomic) reflex depression of cord function below the level of injury, with associated loss of all sensorimotor functions. An initial increase in blood pressure due to the release of catecholamines, followed by hypotension, is noted. Flaccid paralysis, including of the bowel and bladder, is observed, and sometimes sustained priapism develops. These symptoms tend to last several hours to days until the reflex arcs below the level of the injury begin to function again (eg, bulbocavernosus reflex, muscle stretch reflex [MSR]).

Neurogenic shock

Neurogenic shock is manifested by the triad of hypotension, bradycardia, and hypothermia. Shock tends to occur more commonly in injuries above T6, secondary to the disruption of the sympathetic outflow from T1-L2 and to unopposed vagal tone, leading to a decrease in vascular resistance, with associated vascular dilatation. Neurogenic shock needs to be differentiated from spinal and hypovolemic shock. Hypovolemic shock tends to be associated with tachycardia.

Autonomic dysreflexia

See the article Autonomic Dysreflexia in Spinal Cord Injury.

In a study showing a high incidence of autonomic dysfunction, including orthostatic hypotension and impaired cardiovascular control, following SCI, it was recommended that an assessment of autonomic function be routinely used, along with American Spinal Injury Association (ASIA) assessment, in the neurologic evaluation of patients with SCI.³

Motor strengths and sensory testing

The extent of injury is defined by the ASIA Impairment Scale (modified from the Frankel classification), using the following categories^1,2 :

• A - Complete: No sensory or motor function is preserved in sacral segments S4-S5.⁴
• B - Incomplete: Sensory, but not motor, function is preserved below the neurologic level and extends through sacral segments S4-S5.
• C - Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade less than 3.
• D - Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade greater than or equal to 3.
• E - Normal: Sensory and motor functions are normal.

Perform a rectal examination to check motor function or sensation at the anal mucocutaneous junction. The presence of either is considered sacral-sparing.

Definitions of complete and incomplete SCI are based on the above ASIA definition with sacral-sparing.^1,2,4

• Complete - Absence of sensory and motor functions in the lowest sacral segments
• Incomplete - Preservation of sensory or motor function below the level of injury, including the lowest sacral segments

Sacral-sparing is evidence of the physiologic continuity of spinal cord long tract fibers (with the sacral fibers located more at the periphery of the cord). Indication of the presence of sacral fibers is of significance in defining the completeness of the injury and the potential for some motor recovery. This finding tends to be repeated and better defined after the period of spinal shock.

With the ASIA classification system, the terms paraparesis and quadriparesis now have become obsolete. The ASIA classification using the description of the neurologic level of injury is employed in defining the type of SCI (eg, C8 ASIA A with zone of partial preservation of pinprick to T2).

Other classifications of SCI include the following:

• Central cord syndrome often is associated with a cervical region injury and leads to greater weakness in the upper limbs than in the lower limbs, with sacral sensory sparing.
• Brown-Séquard syndrome, which often is associated with a hemisection lesion of the cord, causes a relatively greater ipsilateral proprioceptive and motor loss, with contralateral loss of sensitivity to pain and temperature.
• Anterior cord syndrome often is associated with a lesion causing variable loss of motor function and sensitivity to pain and temperature; proprioception is preserved.
• Conus medullaris syndrome is associated with injury to the sacral cord and lumbar nerve roots leading to areflexic bladder, bowel, and lower limbs, while the sacral segments occasionally may show preserved reflexes (eg, bulbocavernosus and micturition reflexes).
• Cauda equina syndrome is due to injury to the lumbosacral nerve roots in the spinal canal, leading to areflexic bladder, bowel, and lower limbs.

Muscle strength is graded using the following Medical Research Council (MRC) scale of 0-5:

• 5 - Normal power
• 4+ - Submaximal movement against resistance
• 4 - Moderate movement against resistance
• 4- - Slight movement against resistance
• 3 - Movement against gravity but not against resistance
• 2 - Movement with gravity eliminated
• 1 - Flicker of movement
• 0 - No movement

Muscle strength always should be graded according to the maximum strength attained, no matter how briefly that strength is maintained during the examination. The muscles are tested with the patient supine.

The following key muscles are tested in patients with SCI, and the corresponding level of injury is indicated:

• C5 - Elbow flexors (biceps, brachialis)
• C6 - Wrist extensors (extensor carpi radialis longus and brevis)
• C7 - Elbow extensors (triceps)
• C8 - Finger flexors (flexor digitorum profundus) to the middle finger
• T1 - Small finger abductors (abductor digiti minimi)
• L2 - Hip flexors (iliopsoas)
• L3 - Knee extensors (quadriceps)
• L4 - Ankle dorsiflexors (tibialis anterior)
• L5 - Long toe extensors (extensors hallucis longus)
• S1 - Ankle plantar flexors (gastrocnemius, soleus)

Sensory testing is performed at the following levels:

• C2 - Occipital protuberance
• C3 - Supraclavicular fossa
• C4 - Top of the acromioclavicular joint
• C5 - Lateral side of antecubital fossa
• C6 - Thumb
• C7 - Middle finger
• C8 - Little finger
• T1 - Medial side of antecubital fossa
• T2 - Apex of axilla
• T3 - Third intercostal space (IS)
• T4 - Fourth IS at nipple line
• T5 - Fifth IS (midway between T4 and T6)
• T6 - Sixth IS at the level of the xiphisternum
• T7 - Seventh IS (midway between T6 and T8)
• T8 - Eighth IS (midway between T6 and T10)
• T9 - Ninth IS (midway between T8 and T10)
• T10 - 10th IS or umbilicus
• T11 - 11th IS (midway between T10 and T12)
• T12 - Midpoint of inguinal ligament
• L1 - Half the distance between T12 and L2
• L2 - Midanterior thigh
• L3 - Medial femoral condyle
• L4 - Medial malleolus
• L5 - Dorsum of the foot at third metatarsophalangeal joint
• S1 - Lateral heel
• S2 - Popliteal fossa in the midline
• S3 - Ischial tuberosity
• S4-5 - Perianal area (taken as 1 level)

Sensory scoring is for light touch and pinprick, as follows:

• 0 - Absent
• 1 - Impaired or hyperesthesia
• 2 - Intact

A score of zero is given if the patient cannot differentiate between the point of a sharp pin and the dull edge.

Motor level - Determined by the most caudal key muscles that have muscle strength of 3 or above while the segment above is normal (= 5)

Motor index scoring - Using the 0-5 scoring of each key muscle, with total points being 25 per extremity and with the total possible score being 100

Sensory level - Most caudal dermatome with a normal score of 2/2 for pinprick and light touch

Sensory index scoring - Total score from adding each dermatomal score with possible total score (= 112 each for pinprick and light touch)

Neurologic level of injury - Most caudal level at which motor and sensory levels are intact, with motor level as defined above and sensory level defined by a sensory score of 2

Zone of partial preservation - All segments below the neurologic level of injury with preservation of motor or sensory findings (This index is used only when the injury is complete.)

Skeletal level of injury - Level of the greatest vertebral damage on radiograph

Lower extremities motor score (LEMS) - Uses the ASIA key muscles in both lower extremities, with a total possible score of 50 (ie, maximum score of 5 for each key muscle [L2, L3, L4, L5, and S1] per extremity). A LEMS of 20 or less indicates that the patient is likely to be a limited ambulator. A LEMS of 30 or more suggests that the individual is likely to be a community ambulator.

Related eMedicine topics:
Spinal Cord Injuries
Spinal Cord, Topographical and Functional Anatomy
Spinal Cord Trauma and Related Diseases

Epidemiology

Spinal cord injury (SCI) due to trauma is not a common condition, but it has major functional, medical, and financial effects on the injured person, as well as an important effect on the individual's psychosocial well-being.^5,6,7

The most common causes of SCI include the following:

• Motor vehicle accidents (44.5%) - These are the major cause of traumatic SCI in the United States.
• Falls (18.1%) - These are most common in persons at or above age 45 years. Older females with osteoporosis have a propensity for vertebral fractures from falls with associated spinal cord injury.
• Violence (16.6%) - This is the most common cause of SCI in some urban settings in the United States, although a trend toward a slight decrease in violence-related SCI has been found. One study showed that among patients who had suffered an assault, SCI from a penetrating injury tended to be worse than that from a blunt injury.⁸
• Sports injuries (12.7%) - Such injuries are responsible for many cases of SCI. The sport that most commonly leads to SCI is diving.

Other causes of SCI include the following:

• Vascular disorders
• Tumors⁹
• Infectious conditions
• Spondylosis
• Iatrogenic injuries, especially after spinal injections and epidural catheter placement
• Vertebral fractures secondary to osteoporosis
• Developmental disorders

No statistical/epidemiologic data have been compiled for the occurrence of nontraumatic SCI, but cancer alone may account for more SCI than does trauma. Spondylosis is also a common cause of SCI. Traumatic SCI is more common in persons younger than 40 years, while nontraumatic injury is more common in persons older than 40 years.

The incidence of traumatic SCI in the United States is 30-60 new cases per million population, or 10,000 cases per year in the United States. Some sources cite 8 cases per 10,000 population per year.

Figures on estimated prevalence vary from approximately 183,000 to 230,000 cases in the United States, the equivalent of 700-900 cases per million population.

Race

In the United States, the incidence of SCI among whites is higher than among African Americans, which in turn is higher than among Hispanics. Studies indicate that in the United States, 66.4% of SCIs occur in whites; 21.1%, in African Americans; 8.8%, in Hispanics; 1.6%, in Asians; 1.1%, in Native Americans; and 1% in other populations.

Sex

The male-to-female ratio of individuals with SCI in the United States is 4:1; ie, males constitute about 80% of persons with SCI.

Age

More than 50% of all cases of SCI occur in persons aged 16-30 years. The median age is 26.4 years, while the mean age is 31.8 years, and the mode age at injury is 19 years. Traumatic SCI is more common in persons younger than 40 years, while nontraumatic SCI is more common in persons older than 40 years. Greater mortality is reported in older patients with SCI.

In a study on pediatric SCI by Vitale and colleagues, using information from the Kids' Inpatient Database (KID) and the National Trauma Database (NTDB), it was found that, with regard to the annual incidence rate of pediatric SCI, there were significant differences between patient populations (as stratified by race and sex).¹⁰  A significantly greater incidence of pediatric SCI was found in African Americans (1.53 cases per 100,000 children) than in Native Americans (1.0 case per 100,000 children) and Hispanics (0.87 case per 100,000 children). The frequency in Asians was significantly lower than that in all other races (0.36 per 100,000 children).

Also, the likelihood that boys would suffer SCI was found to be more than twice that of girls (2.79 cases per 100,000 children vs 1.15 cases per 100,000 children, respectively). The overall incidence of pediatric SCI is 1.99 cases per 100,000 US children. As estimated from the above data, 1455 children are admitted to US hospitals annually for SCI treatment.

Vitale and coauthors looked at the major causative factors of pediatric SCI as well, with the following incidences reported¹⁰ :

• Motor vehicle accidents - 56%
• Accidental falls - 14%
• Firearm injuries - 9%
• Sports injuries - 7%

Among children in the study, 67.7% of those injured in a motor vehicle accident were not wearing a seatbelt. Alcohol and drugs were found to have played a role in 30% of all pediatric SCI cases.

Associated injuries

Other injuries are often associated with traumatic SCI, including bone fractures (29.3%), loss of consciousness (17.8%), and traumatic brain injury affecting emotional/cognitive functioning (11.5%).

Marital status

Single persons sustain SCIs more commonly than do married persons. Research has indicated that among persons with SCI whose injury is approximately 15 years old, one third will remain single 20 years postinjury. The marriage rate after SCI is annually about 59% below that of persons in the general population of comparable gender, age, and marital status.
 
The divorce rate annually among individuals with SCI within the first 3 years following injury is approximately 2.5 times that of the general population, while the rate of marriages contracted after the injury is about 1.7 times that of the general population. Marriage is more likely if the patient is a college graduate, previously divorced, paraplegic (not tetraplegic), ambulatory, living in a private residence, and independent in the performance of activities of daily living (ADL).

The divorce rate among persons with SCI who were married at the time of injury is higher if the patient is younger, female, African American, without children, nonambulatory, and previously divorced. The divorce rate among those who were married after the SCI is higher if the individual is male, has less than a college education, has a thoracic level injury, and was previously divorced.

Educational status

The rate of injury differs according to educational status, as follows:

• Less than a high school degree at 39.8%
• High school degree - 49.9%
• Associate degree - 1.6%
• Bachelors degree - 5.9%
• Masters or doctorate degree - 2.1%
• Other degree - 0.7%.

Level and type of injury

The most common levels of injury on admission are C4, C5 (the most common), and C6, while the level for paraplegia is the thoracolumbar junction (T12). The most common type of injury on admission is ASIA level A.

Season

SCIs occur most frequently in July and least commonly in February. The most common day on which SCIs occur is Saturday. SCIs occur more frequently during daylight hours, which may be due to the increased frequency of motor vehicle accidents and of diving and other recreational sporting accidents during the day.

Substance abuse

The rate of alcohol intoxication among individuals who sustain SCI is 17-49%.

Injuries by ASIA classification

• Incomplete tetraplegia - 29.5%
• Complete paraplegia - 27.9%
• Incomplete paraplegia - 21.3%
• Complete tetraplegia - 18.5%

The most common neurologic level of injury is C5. In paraplegia, T12 is the most common level.

Employment

Patients with SCI classified as ASIA D are more likely to be employed than individuals with ASIA A, B, and C. Persons employed tend to work full-time. Individuals who return to work within a year of injury tend to return to the same job. Those individuals who return to work after a year of injury tend to work for a different employer at a different job requiring retraining.¹¹

The likelihood of employment after injury is greater in patients who are younger, male, and white and who have more formal education, higher reported intelligence quotient (IQ), greater functional capacity, and less severe injury. Patients with greater functional capacity, less severe injury, history of employment at the time of injury, greater motivation to return to work, nonviolent injury, and ability to drive are more likely to return to work, especially after more elapsed time following injury.

Life expectancy

Approximately 10-20% of patients who have sustained an SCI do not survive to reach acute hospitalization, while about 3% of patients die during acute hospitalization. Patients aged 20 years at the time they sustain an SCI have a life expectancy of approximately 33 years (patients with tetraplegia), 39 years (patients with low tetraplegia), or 44 years (patients with paraplegia). Individuals aged 60 years at the time of injury have a life expectancy of approximately 7 years (patients with tetraplegia), 9 years (patients with low tetraplegia), and 13 years (patients with paraplegia). The annual death rate for patients with acute SCI is 750-1000 deaths per year in the United States.

Studies have found that patients with SCI who suffer from pain have less life satisfaction than do patients in whom pain is well controlled; this may also affect the patients' general outlook on life.^12,13  A 2006 study by Strauss and colleagues reported that among patients with SCI, during the critical first 2 years following injury, a 40% decline in mortality occurred between 1973 and 2004.¹⁴ The study also found that during that same 31-year period, there had been only a small, statistically insignificant reduction in mortality in the post 2-year period for these patients.

Leading cause of death

The leading causes of death in patients following SCI are pneumonia and other respiratory conditions, followed by heart disease, subsequent trauma, and septicemia.^15,16 Suicide and alcohol-related deaths are also major causes of death in patients with SCI.^17,18 In persons with SCI, the suicide rate is higher among individuals who are younger than 25 years.

Among patients with incomplete paraplegia, the leading causes of death are cancer and suicide (1:1 ratio), while among persons with complete paraplegia, the leading cause of death is suicide, followed by heart disease.

Related eMedicine topic:
Spinal Cord Injury and Aging

Keywords

spinal cord injury, spine, spinal, spinal cord, paralysis, paralyzed, spinal injury, cervical spine, paraplegia, quadriplegia, paraplegic, quadriplegic, spinal injuries, spinal cord injuries, injury to spinal cord, central cord syndrome, tetraplegic, tetraplegia, complete spinal cord injury, incomplete spinal cord injury, Brown-Séquard syndrome, anterior cord syndrome, conus medullaris syndrome, cauda equina syndrome

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