Spinal Cord Injury

Spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent change in motor, sensory or autonomic function below the level of injury. The distinction between a complete injury (ASIA A) and an incomplete one (ASIA B-D) is crucial for prognosis.

Mechanism. The causes, in order of frequency:

• Motor vehicle accidents - 39%
• Falls - 31%, and increasing in the elderly
• Violence - 14%, predominantly gunshot wounds
• Sports - 8%, with diving injuries common
• Medical and surgical complications - 5%

Level. By region:

• Cervical - 55%, with the worst outcomes
• Thoracic - 30%, from high-velocity injuries
• Lumbar - 15%, often with burst fractures

Age. The distribution has two peaks: young adults aged 15-29 injured in trauma, and people over 65 who fall onto a cervical spine with pre-existing stenosis. The elderly are a growing proportion of SCI patients.

Global burden. Traumatic SCI occurs in roughly 8 to 50 per million people per year, with the highest rates in regions carrying a heavy burden of road-traffic injury and falls.

The cord. The spinal cord ends at L1-L2 as the conus medullaris. It has two enlargements for the limbs: cervical (C4-T1) for the upper limb and lumbar (L1-S2) for the lower. In cross-section the grey matter is central, motor anteriorly and sensory posteriorly, and the white matter tracts lie peripherally around it.

Primary injury. The mechanical disruption at the moment of trauma, by compression, contusion or transection. It is not reversible.

Secondary injury. The damage that follows over hours to days, and the part that can be prevented:

• Ischaemia from hypotension
• Oedema and inflammation
• Excitotoxicity from glutamate release
• Apoptosis (programmed cell death)

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The ASIA Impairment Scale is the standard classification for SCI worldwide. It grades completeness; the ISNCSCI examination, in the last tab, defines the level.

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ASIA ClassificationIncomplete SyndromesKey Muscle GroupsLevel & ZPP

Grades B to D are the incomplete injuries, defined by sacral sparing.

• A - Complete. No motor or sensory function in the sacral segments S4-S5: no voluntary anal contraction and no perianal sensation.
• B - Sensory incomplete. Sensory function preserved below the level, including S4-S5, with no motor function below the level.
• C - Motor incomplete. Motor function preserved below the level, but more than half of the key muscles below it have grade less than 3.
• D - Motor incomplete. Motor function preserved below the level, with half or more of the key muscles grade 3 or greater.
• E - Normal. Full motor and sensory function, although the reflexes may be abnormal.

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Central cord syndrome is the most common incomplete pattern, usually from hyperextension with stenosis. The upper limbs are worse than the lower limbs. Sensory loss below the level is variable, and a suspended, cape-like loss is the signature of syringomyelia, not of central cord syndrome. The prognosis for ambulation is favourable, but fine hand recovery is often incomplete.

Brown-Séquard syndrome is a hemisection of the cord, often from penetrating trauma. Motor function and proprioception are lost on the same side, pain and temperature on the opposite side. It carries a good prognosis for ambulation, the best of the incomplete syndromes.

Anterior cord syndrome damages the anterior two-thirds of the cord and spares only the dorsal columns. Motor loss is complete and pain and temperature are lost, while proprioception and vibration are preserved. It has the worst prognosis of the incomplete syndromes.

Posterior cord syndrome is rare: proprioception and vibration are lost with motor function preserved. It is usually caused by tumours or vitamin B12 deficiency.

Ten paired myotomes are tested on both sides.

C5

Muscle

Elbow flexors

Action

Biceps

C6

Muscle

Wrist extensors

Action

ECRL/ECRB

C7

Muscle

Elbow extensors

Action

Triceps

C8

Muscle

Finger flexors

Action

FDP to middle finger

T1

Muscle

Finger abductors

Action

Small finger abduction

L2

Muscle

Hip flexors

Action

Iliopsoas

L3

Muscle

Knee extensors

Action

Quadriceps

L4

Muscle

Ankle dorsiflexors

Action

Tibialis anterior

L5

Muscle

Long toe extensors

Action

EHL

S1

Muscle

Ankle plantarflexors

Action

Gastrocnemius

Level	Muscle	Action
C5	Elbow flexors	Biceps
C6	Wrist extensors	ECRL/ECRB
C7	Elbow extensors	Triceps
C8	Finger flexors	FDP to middle finger
T1	Finger abductors	Small finger abduction
L2	Hip flexors	Iliopsoas
L3	Knee extensors	Quadriceps
L4	Ankle dorsiflexors	Tibialis anterior
L5	Long toe extensors	EHL
S1	Ankle plantarflexors	Gastrocnemius

Power is graded 0-5 on the MRC scale: 0 is no movement, 3 is movement against gravity and 5 is normal.

The ASIA grade (A-E) describes completeness; the ISNCSCI examination also defines where the injury is. Examiners frequently ask you to define these four terms precisely.

Sensory level

Definition

The most caudal dermatome with NORMAL (2/2) light touch AND pinprick on both sides (with everything above also normal)

Motor level

Definition

The most caudal key muscle with power at least grade 3, PROVIDED the key muscle immediately above is grade 5 (where there is no testable myotome, the motor level follows the sensory level)

Neurological level of injury (NLI)

Definition

The most caudal segment with NORMAL sensory AND antigravity (3+) motor function on both sides, with normal function above it - a single summarising level

Zone of partial preservation (ZPP)

Definition

ONLY in complete (ASIA A) injuries: the dermatomes/myotomes BELOW the level that retain some (partial) sensory or motor function; recorded as the most caudal partially-innervated segment

Term	Definition
Sensory level	The most caudal dermatome with NORMAL (2/2) light touch AND pinprick on both sides (with everything above also normal)
Motor level	The most caudal key muscle with power at least grade 3, PROVIDED the key muscle immediately above is grade 5 (where there is no testable myotome, the motor level follows the sensory level)
Neurological level of injury (NLI)	The most caudal segment with NORMAL sensory AND antigravity (3+) motor function on both sides, with normal function above it - a single summarising level
Zone of partial preservation (ZPP)	ONLY in complete (ASIA A) injuries: the dermatomes/myotomes BELOW the level that retain some (partial) sensory or motor function; recorded as the most caudal partially-innervated segment

Completeness depends on the sacral segments, not the NLI

Whether an injury is complete or incomplete is decided only at S4-S5 (deep anal pressure, S4-5 light touch/pinprick, voluntary anal contraction) - NOT at the injury level. ZPP is a concept reserved for complete (ASIA A) injuries; in an incomplete injury there is, by definition, preserved sacral function so the term does not apply. A common error is to quote a "zone of partial preservation" in an ASIA B-D patient.

Primary survey. Assessment starts with the primary survey, the cervical spine controlled throughout:

• Airway - intubation may be needed
• Breathing - diaphragm function (C3-5) and respiratory assessment
• Circulation - is there neurogenic shock, with bradycardia and hypotension?
• Disability - GCS, pupils and gross neurology
• Exposure - complete spinal examination with a log roll

The ASIA examination. Test the 10 key muscles on both sides on the 0-5 scale, and light touch and pinprick in 28 dermatomes. Test the bulbocavernosus reflex for spinal shock, examine the sacral segments, and document the neurological level and ASIA grade clearly.

Neurogenic shock is cardiovascular. Loss of sympathetic vascular tone causes hypotension, with warm, dry peripheries from vasodilation, and the unopposed parasympathetic supply to the heart causes bradycardia. It occurs with lesions above T6.

Spinal shock is neurological, and it is not the same thing. Below the injury level there is transient areflexia and flaccid paralysis, not yet spasticity, even if the injury is complete; anal tone is lost and the bulbocavernosus reflex is initially absent. It typically resolves over 24-72 hours, and the return of the bulbocavernosus reflex signals its end.

CT defines the bony injury.

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MRI timing. MRI should not delay resuscitation or surgery in an unstable patient. For an incomplete injury with unclear pathology, MRI within 24 hours helps guide surgical planning. What the cord looks like predicts how it will do:

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The patient who cannot move their limbs after trauma is not always a structural cord injury. Distinguishing true SCI from its mimics changes management entirely, and confusing complete with incomplete patterns alters prognosis and surgical urgency.

Neurogenic bladder. The pattern of bladder dysfunction depends on whether the lesion is above or at or below the sacral micturition centre (S2-S4), a high-yield distinction with direct consequences for management.

Rehabilitation. Transfer to a spinal rehabilitation unit as soon as the patient is medically stable. Multidisciplinary care from physiotherapy, occupational therapy, psychology and social work significantly improves functional outcomes.

Recovery by grade. Most neurological recovery occurs in the first 6-12 months, and how much depends on the ASIA grade:

• ASIA A - less than 5% regain functional ambulation. Recovery plateaus within 1 year, and the focus is on maximising function at the level of injury
• ASIA B - 50% regain some walking ability. The prognosis is better than for a complete injury, and early surgery may improve outcomes
• ASIA C - 75% improve at least one ASIA grade, and most will achieve some ambulation
• ASIA D - 95% maintain community ambulation, an excellent functional prognosis

Global Epidemiology

• Reported incidence of traumatic SCI varies widely, roughly 8 to 50 per million population per year, reflecting differences in road safety, violence and ascertainment.
• Bimodal age distribution: young adults (high-energy trauma) and an expanding elderly group (low-energy falls on a stenotic, often degenerate cervical spine).
• Worldwide the cervical spine is the commonest level injured, and males predominate, though the elderly fall cohort narrows this gap.
• High-income settings have seen falling SCI prevalence (Global Burden of Disease 2017 reported a decline in US SCI prevalence), while road-traffic SCI remains a major and rising burden in many low- and middle-income countries.

Major Guidelines Side by Side

High-Resource vs Limited-Resource Practice

SCI management contains several genuinely unresolved questions, the steroid debate under Management among them. Examiners reward a candidate who can argue both sides rather than recite a single dogmatic answer.

How early is early surgery? STASCIS supports decompression within 24 hours. Emerging data and meta-analyses argue for an even tighter "ultra-early" window of under 8 to 12 hours, especially for cervical injuries. The counter-argument is logistical feasibility and the risk of operating on a haemodynamically unstable patient.

The MAP target and its duration. The 85-90mmHg for 5-7 days target is widely cited but rests on small case series, not RCTs. Some argue the threshold should be individualised using spinal cord perfusion pressure (MAP minus intrathecal pressure) measured through an intrathecal catheter, an investigational approach.

Timing in central cord syndrome. Traditional teaching favoured conservative management, given good spontaneous recovery. The 2017 AOSpine guideline now suggests early surgery as an option even in central cord syndrome, though on low-quality evidence, and practice remains genuinely divided.