IN BRIEF
Classifications In Brief: American Spinal Injury Association
(ASIA) Impairment Scale
Timothy T. Roberts MD, Garrett R. Leonard MD, Daniel J. Cepela MD
Received: 20 May 2016 / Accepted: 17 October 2016 / Published online: 4 November 2016
Ó The Association of Bone and Joint Surgeons1 2016
History
There are approximately 12,500 spinal cord injuries in the
US annually [15], with global incidence ranging from
133,000 to 226,000 cases annually [8]. The cost associated
with spinal cord injuries is substantial, with estimates of
the average lifetime cost of direct care ranging from USD
1.5 to 4.7 million [15]. Motor vehicles are the leading
cause of injury, and are becoming an increasingly common
cause in developing nations [15]. The demographics of
patients with spinal cord inj uries have broadened with time,
however, males still account for 80% of new patients with
spinal cord injuries [15].
The American Spinal Injury Association was created in
1973 to facilitate the exchange of research, data, and ideas
among practitioners involved in the treatment of patients
with spinal cord injuries. Its founders sought to establish a
standardized model of care for the growing number of
patients with spinal cord injuries. Before this, the Frankel
scale had been developed to categorize spinal cord injuries
[3]. However, the Frankel scale had considerable limita-
tions. It did not specify the level of spine injury in its
classification. It also did not define the difference between
‘motor useful’ and ‘motor useless’ grades, leading to sub-
jective grading. [17]. In 1982, the American Spinal Injury
Association published the International Standards for
Neurological Classification of Spinal Injury [1], a grading
and classification system that would evolve into the current
American Spinal Injury Association Impairment Scale
(AIS) [7]. Among its notable contributions, the Interna-
tional Standards for Neurological Classification of Spinal
Injury classification helped identify key muscle groups and
sensory po ints that improved prac titioners’ precision at
identifying neurologic levels of injury. In addition, it was a
reproducible classification with detailed descriptions of
each sensory and motor grade. This allowed accurate
characterization of incomplete and complete spinal cord
injuries [9].
The AIS replaced the modified Frankel scale and
became the international gold standard for evaluation of
spinal cord injuries [17]. Since its inception, the AIS has
been revised multipl e times as its authors continue to refine
the steps of the neurologic examination and details of the
classification grades. These revisions have improved
reproducibility of the AIS and allowed for better under-
standing of the scale’s therapeutic and implications [17].
Purpose
The purpose of the AIS is to (1) standardize careful,
detailed d ocumentation of spinal cord injuries, (2) guide
further radiographic assessment and treatment, and (3)
Each author certifies that he or she, or a member of his or her
immediate family, has no funding or commercial associations (eg,
consultancies, stock ownership, equity interest, patent/licensing
arrangements, etc) that might pose a conflict of interest in connection
with the submitted article.
All ICMJE Conflict of Interest Forms for authors and Clinical
Orthopaedics and Related Research
1
editors and board members are
on file with the publication and can be viewed on request.
T. T. Roberts (&)
Cleveland Clinic Neurological Institute, 9500 Euclid Avenue,
S40, Cleveland, OH 44113, USA
e-mail: timothy.t.roberts@gmail.com
G. R. Leonard, D. J. Cepela
Division of Orthopaedic Surgery, Albany Medical Center,
Albany, NY, USA
123
Clin Orthop Relat Res (2017) 475:1499–1504
DOI 10.1007/s11999-016-5133-4
Clinical Orthopaedic
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and Related Research
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A Publication of
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determine whether injuries are complete or incomplete—an
important and often subtle neurologic distinction that has
tremendous prognostic implications [17].
In addition to standardizing practice and aiding research,
the AIS has practical clinical utility. The AIS can help pro-
viders answer difficult quest ions such as ‘‘will the patient
ever walk again?’’ [17]. The AIS also may help predict
recovery of autonomic functions such as bowel, bladder,
cardiovascular, respiratory, and reproductive functions,
although this remains a topic for further study [ 17].
Description of the AIS
The AIS is a standardized examination consisting of a
myotomal-based motor examination, dermatomal based
sensory examination, and an anorectal examination. Based
on the findings of these examin ations, an injury severity or
grade and level are assigned (Fig. 1).
The sensory examination evaluates 28 specific der-
matomes bilaterally for light touch (generally a piece of
cotton) and pinprick (generally a clean safety pin) sensa-
tion. Each examination component is recorded for each
dermatome and laterality. A grade of 0 denotes absent
sensation, 1 denotes impaired or altered sensation, and 2
denotes normal sensation. A normal unilateral sensory
examination consists of 28 dermatomes each with 2/2
points for light touch and 2/2 points for pinprick, yielding
112 total points. A total score of 224 bilaterally is a fully
normal sensory examination. Inability to distinguish pin-
prick sensation from light touch is technically graded as 0
[11].
The motor examination consists of grading five specific
muscle groups in the upper extremities and five specific
Fig. 1 The American Spinal Injury Association International Stan-
dards for Neurological Classification of Spinal Cord Injury form used
to evaluate spinal cord injury is presented. (American Spinal Injury
Association. International Standards for Neurological Classification
of Spinal Cord Injury. Atlanta, GA, Revised 2011, Updated 2015.
Published with permission of the American Spinal Injury Association,
Richmond, VA, USA.)
1500 Roberts et al. Clinical Orthopaedics and Related Research
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muscle groups in the lower extremities, representing major
cervical and lumbar myotomes (Table 1). Motor strength is
graded using a universal six-point scale (graded as 0–5)
(Table 2). Motor strength is recorded for each muscle
group bilaterally. The maximum bilateral motor score in a
healthy individual is 100, 50 for scoring 5/5 in all right
upper and lower extremity myotomes, and another 50 for
the left.
The additional anorectal examination is essential for
determining the completeness of the injury and evaluating
for the presence of spinal shock. The external anal
sphincter is examined digitally for voluntary motor con-
traction and the ability to sense deep anal pressure. Both
are graded in a binary fashion, 0 for absent and 1 for
present. The bulbocavernosus reflex is assessed via digital
rectal examination, during which a palpable internal and
external anal sphincter contraction occur s in response to
squeezing the glans penis or clitoris. Tugging on an
indwelling urinary catheter also may elicit the reflex.
The AIS also includes the level of neurologic injury in
its classification. As stated, this is defined as the most
caudal functioning root level with intact sensation and
Grade 3 or greater motor function; however, the lowest
normal sensory level may be substituted in regions without
readily testable myotomes (such as in the thoracic spine).
The AIS further classifies injuries as a complete or
incomplete spinal cord injury. A complete spinal cord
injury is defined as the absence of all motor and sensory
functions, including sacral roots, distal to the site of injury.
These injuries are designated as being Grade A on the AIS.
Incomplete injuries are defined as those with some degree
of retained motor or sensory function below the site of
injury. These are graded B through E on the AIS (Table 3).
Patients with AIS Grade B injuries have some sensory
Table 1. Key myotomes and dermatomes for extremity neurologic testing
Upper extremity Lower extremity
Root Functional group Myoterm Dermatome Root Functional group Myoterm Dermatome
C5 Elbow flexors Biceps, brachialis Lateral shoulder L2 Hip flexors Iliopsoas Anterior mid-thigh
C6 Wrist extensors Extensor carpi
radialis longus,
Extensor carpi
radialis brevis
Lateral forearm,
dorsum of
thumb and
index finger
L3 Knee extensors Quadriceps Anterior knee
C7 Elbow extensors Triceps Dorsum of
middle finger
L4 Ankle
dorsiflexors
Tibialis
Anterior
Medial leg and
medial malleolus
C8 Finger flexors Flexor digitorum
profundus (middle
finger)
Dorsum of ring
and small
finger
L5 Long toe
extensors
Extensor
halluces
longus
Lateral leg, medial
dorsum foot
T1 Finger abductors Abductor digiti
minimi (small
finger)
Medial forearm S1 Ankle plantar
flexors
Gastrocsoleus
complex
Distal calf, lateral
plantar foot
Table 2. Muscle strength and sensory grading
Muscle function grading Sensory grading
0 = total paralysis 0 = Absent (or inability to tell sharp from dull)
1 = palpable or visible contraction 1 = Altered, either decreased or impaired
sensation or hypersensitivity
2 = active movement, full ROM with gravity eliminated 2 = Normal
3 = active movement, full ROM against gravity NT = Not testable
4 = active movement, full ROM against gravity and moderate resistance in a muscle specific
position
5 = (normal) active movement, full ROM against gravity and full resistance in a functional
muscle position expected from an otherwise unimpaired person
5* = (normal) active movement, full ROM against gravity and sufficient resistance to be
considered normal if identified inhibiting factors (ie, pain, disuse) were not present
NT = not testable (ie, attributable to immobilization, severe pain such that the patient cannot be
graded, amputation of limb, or contracture greater than 50% of the normal ROM)
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function but no motor function. AIS Grade C injuries have
a motor grade less than 3 below the neurologic level of
injury while AIS Grade D injuries have a motor grade of at
least 3 below the neurologic level of injury. Patients with
Grade E injuries have normal motor and sensory exami-
nations, but still may have abnormal reflex es or other
neurologic phenomena [17].
The determination of a complete or incomplete spinal
cord injury requires resolution of spinal shock. Spinal
shock is a physiologic response to trauma that is marked by
initial depolarization of axonal tissue immediately after
injury. During spinal shock, the patient exhibits a transient
period of flaccid paralysis during which time he or she is
areflexic. Notably, this includes absen ce of the bulbocav-
ernosus reflex. After return of this reflex, the patient can be
assessed accurately for complete versus incomplete injury.
Finally, a complete and meaningful examination cannot be
performed in patients with altered or limited consciousness
(such as might occur with intoxication, head injury, intu-
bation) or in the presence of an untreated major distracting
injury.
Validation
Multiple studies investigating the intra- and interobserver
reliability of the AIS show overall good reliability for
motor and sensory (pin prick and light touch) testing
[2, 12–14, 16, 22]. Correlation coefficients for intra- and
interobserver motor and sensory assessment generally are
quoted as 0.90 or greater, which reflects generally high
agreement [4, 14]. Incomplete injuries tend to exhibit
weaker intra- and interobserver correlations than those with
more ‘‘cut-and-dry’’ complete injuries [22].
The AIS has strong prognostic value that has been
shown across various functional outcomes [18, 19, 21]. van
Middendorp et al. [18] reported excellent predictive values
of the AIS scores regarding predicting independent
ambulation at 1 year. They found that patients with AIS
Grade A injuries have a 91.7% (95% CI, 87.4%–94.8%)
negative predictive probability for independent ambulatory
ability, whereas those with AIS Grade D injuries have a
97.3% (95% CI, 92.2%–99.4%) positive predictive proba-
bility of regaining independent ambulation at 1 year [18].
van Middendorp et al. [18, 20] reported superiority of these
prognostic factors over the clinical practice of distin-
guishing injuries as ‘‘complete’’ or ‘‘incomplete;’’
however, the prognostic accuracy of Grades B and C
injuries are considerably less consistent. The presence of
postinjury somatosensory evoked potentials in the tibial
nerve, among others, have been strongly related to ambu-
latory outcomes. However, neurophysiologic testing does
not offer additional prognostic accuracy over information
gleaned from the AIS examination [5].
Diagnosis of an AIS Grade A injury after resolution of
spinal shock has a remar kably strong—albeit unfortunate—
correlation with future inability to regain functional motor
capacity [6, 21]. Kirshblum et al. [6] presented a longitu-
dinal study of patients with spinal cord injury and found
that only 2.1% patients with a complete injury improved to
having an incomplete injury by 5 years.
When examining the AIS by its components, the lowest
rates of intra- and interobserver reliability involve asse ss-
ment of anorectal function and determination of sacral
sparing [14, 22]. van Middendorp et al. [20] reported that
the anorectal examination and presence of sacral sparing
correlated only with prognosis in the setting of chronic
injury; in the acute phase, where such functions may be
masked by unrecognized spinal shock, reliability is
diminished [20
].
Limitations
The most fundamental limitation of the AIS may be
obvious given its title: it is an impairment scale that does
not report the objective anatomic nature of the causal
injury. It also does not determine injury severity. For
example, a complete AIS Grade A injury in the lower
lumbar spine can lead to bowel or bladder dysfunction with
foot-drop, but an otherwise ambulatory and independently
functional lifestyle. By contrast, the ostensibly less severe
AIS Grade C or D injury in the upper cervical spine can
still render patients quadriplegic and largely dependent on
Table 3. American Spinal Injury Association Impairment Scale
A Complete No motor or sensory function is preserved in the sacral segments S4–S5.
B Incomplete Sensory function preserved but not motor function is preserved below the neurological level and includes the sacral segments
S4–S5.
C Incomplete Motor function is preserved below the neurological level, and more than half of key muscles below the neurological level have a
muscle grade less than 3.
D Incomplete Motor function is preserved below the neurological level, and at least half of key muscles below the neurological level have a
muscle grade of 3 or more.
E Normal Motor and sensory function are normal.
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support. In its defense, use of the AIS grade without an
associated level is not its intended application.
A second criticism of the AIS is that it does not account
for pain, spasticity, or dysesthesia that might result from
spinal cord injury, but only the ability to sense pinprick and
light touch. In reality, patients with AIS Grade E injuries
may score as having ‘‘normal’’ motor and sensory function
but still show marked disability from such neurologic
phenomena.
A third limitation of the AIS is that, with a few
notable exceptions [12, 22], a study of its reliability is
limited to adult patients [10]. It has been shown that chil-
dren as young as 6 years are able to consistently comply
with the examination, however, this was evaluated only in
patients with chronic spinal cord injuries [13]. It is likely
that in patients with an acute injury, the ability of the
patient to comply with the examination would be limited
by stress, pain, and the presence of med ications.
Finally, we do not know the minimal clinically important
difference of the AIS [10]. In other words, there is not an
agreed-upon threshold above which a given medical or sur-
gical intervention can be clearly said to be benefic ial. While
numerous authors agree that improvement in a single AIS
letter grade is a substantial and desirable improvement
[16, 20], gaining a couple of points for one’s nume rical
American Spinal Injury Association score may not result in
tangible benefits. In addition, not all points are created
equally: gaining a motor grade or two in a key muscular
group may be the difference between ambulating and
requiring a wheelchair; however, gaining the same number
of points in one’s thoracic sensory levels, for example, is less
likely to make a tangible effect on quality of life.
Conclusions and Uses
A spinal cord injury is a relatively common occurrence
with devas tating complications. When examining a patient
with spinal cord injuries, a detailed and carefully per-
formed neurologic assessment is paramount. Testing
consists of motor strength and sensory function at various
key myotomes and dermatomes. The purpose of the AIS is
to (1) standardize careful, detailed documentation of an
injury, (2) guide further radiographic assessment and
treatment, and (3) determine whether injuries are complete
or incomplete, an important and som etimes subtle neuro-
logic distinction that has tremendous prognostic
implications. Complete spinal cord injuries are defined by
the absence of all motor and sensory functions below the
site of injury, whereas incomplete spinal cord injuries will
retain variable motor and/or sensory function. Diagnosing
complete or incomplete spinal cord injuries requires reso-
lution of spinal shock. The AIS classification has
tremendous prognostic value. This allows for better patient
counseling regarding expectations of recovery. It also
precisely defines the level and degree of a patient’s deficit,
allowing treatments and therapy to be tailored to a patient’s
individual needs.
References
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