Neurologic evaluation of nerve root syndromes

The differential diagnosis of nerve root syndromes requires a working knowledge of the innervation patterns of the spinal nerve roots (including dermatomes, myotomes, and sclerotomes) and the peripheral nerves. Normal anatomical variations and overlapping patterns of segmental innervation require testing not only the key muscles and dermatomes in the suspected spinal region, but also the key muscles and dermatomes in the spinal segments above and below the suspected lesion. We recommend that the practitioner use the following reference charts on innervations and the more common nerve root syndromes as a guide to the neurologic evaluation of patients with suspected nerve root involvement.

¦ Sensory innervation of the skin

When testing for sensory paraesthesias, the manual therapist differentiates patterns of peripheral nerve innervation from segmental cutaneous innervation (dermatome). Figure 7.1 and Figure 7.2 demonstrate the overlap between these multiple sources of cutaneous innervation. When a patient reports diffuse sensory disturbance there can be a significant amount of der-matomal overlap. Patterns of peripheral innervation are more clearly delineated.

N. trigeminus N. auricularis magnus N. cutaneus colli Nn. supraclaviculares N. axillaris (N. cut. brachii lat.)


Ri. vent, nervor. intercost.

N. cut. brachii med.

N. radialis (N. cut. brachii post.)

Ri. lat. nervor. intercost.

N. musculocutaneus (N. cut antebrachii lat.)

N. cut. antebrachii med.

N. radialis N. medianus N. ulnaris

N. iliohypogastricus N. ilioinguinalis N. genitofemoralis N. cut femoris lat.

N. obturatorius

N. femoralis (Ri. cut. fern, ant.)

N. saphenus

N. cut. surae lat.

N. suralis N. fibularis sup. N. fibularis prof.

Figure 7.1

Dermatomes and peripheral innervation of the ventral side of the human body

N. frontalis (V-|)

Figure 7.2

Dermatomes and peripheral innervation of the dorsal side of the human body


N. occipitalis major

N. occipitalis minor N. auricularis magnus Ri. dors, nervor. spinal, cerv.

Nn. supraclaviculares

N. axillaris (N. cut. brachii lat.)

Ri. dors, nervor. spin, thorac.

N. radialis (N. cut. brachii post.)

N. cutaneus brachii med.

Ri. lat. nervor. intercost.

N. cut. antebrachii med.

N. musculocutaneus (N. cut. antebrachii lat.)

N. iliohypogastricus N. radialis N. ulnaris N. medianus

Nn. clunium sup., med., inf.

N. cut. femoris lat.

N. cut. femoris post.

N. obturatorius

N. saphenus N. cut. surae lat.

N. suralis

N. plantaris lat.

N. plantaris med.

Sensory innervation of deep structures

The segmental innervation of muscles (myotome), ligaments, and the periosteum (sclerotome) often differs from segmental cutaneous innervation (dermatome), especially in the extremities, the shoulder girdle, and the pelvis. For example, at the inferior angle of the scapula, the periosteum, the vascular supply, and the muscles are innervated by C8 (Figure 7.3) while the overlying skin is innervated by the T6 and T7 nerve roots (Figure 7.2).

Figure 7.3

Myotomes and sclerotomes of the right upper extremity with the shoulder girdle and the right lower extremity, dorsal view (from Inman and Saunders, 1944)


Motor innervation

In the presence of motor loss, the manual therapist first determines whether the weakness is of peripheral or central origin. Monoradicular lesions are distal to the ventral horn and therefore can only be flaccid (not spastic). These paresis can be differentiated with the use of manual muscle testing, evaluation of muscle atrophy, and electromyography or chronaximetry.

Almost all muscles in the body, even the smallest, are innervated by more than one nerve root. Those muscles innervated mainly by one root are the key muscles most useful in the evaluation of spinal nerve root lesions. Any loss of function or atrophy in a key muscle implicates a possible nerve root lesion at a particular spinal segment.

Monoradicular loss can also present with atrophy of certain small distal muscles of the extremities, indicating that the remaining nerve root(s) involved in innervation of this muscle cannot offset the weakness caused by the involved nerve.

¦ Common nerve root syndromes

Table 2: Cervicothoracic nerve root syndromes

Root

Key Muscle(s)

Reflex

Dermatome

Cl

Intrinsic upper cervicai fiexors and extensors between 0-C1

C2

Intrinsic upper cervicai rotators between C1-C2

Posterior head

C3

Scaieni

’’Shawl”

C4

Diaphragm

’’Epaulets”

C5

Biceps brachii

Infraspinatus and supraspinatus

Biceps tendon refiex

Shoulder and lateral side of upper arm

C6

Brachioradialis Wrist extensors

Brachioradialis refiex Radiaiperiosteal refiex

Forearm (radiai side) Thumb and index finger

C7

Triceps brachii Wrist fiexors Finger extensors Abductor poiiicis brevis Opponens poiiicis

Triceps tendon reflex

Forearm (dorsai side) Middie and index finger

C8

Flexor digitorum Adductor poiiicis Abductor digiti minimi

Thumb reflex

Forearm (ulnar side) Smaii and ring fingers

T1

Interossei

Arm (medial side)

Table 3: Lumbosacral nerve root syndromes

Root

Key Muscle(s)

Reflex

Dermatome

L1-2

Cremaster

Cremasteric reflex

Waist “backbeit"

L2-3

Hip adductors

Adductor reflex

Ventral thigh down to the knee

L4

Tibialis anterior Quadriceps (vastus medialis)

Patellar tendon reflex

Medial side of lower leg down to the malleolus

L5

Extensor hailucis longus Extensor digitorum iongus and brevis Tibiaiis posterior

Tibialis posterior refiex Semitendinous reflex

Dorsal foot Big toe

S1

Peroneais

Triceps surae (primariiy gastrocnemius, mediai)

Achilles tendon reflex

Laterai foot and soie Smaii toe

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