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12.11 Radicular Lesions: Motor Deficits

A Indicator musdes of radicular lesions—limb musdes and diaphragm (after Kunze)

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Location of pain or sensory disturbance

Indicator muscle

Reflexes abolished by a segmental lesion

While a lesion of the sensory dorsal roots leads to sensory disturbances in specific dermatomes (see p. 344 and C, p. 345), a lesion of the motor ventral roots will cause weakness to develop in specific musdes. Just as the affected dermatome indicates the site of the sensory root lesion, the affected muscle indicates the level of the damaged spinał cord segment or its root. The musdes that are predominantly supplied by a particular spinał cord segment are called its indicator musdes (analogous to the dermatomes for the dorsal roots). Because indicator musdes are supplied predominantly but, as a rule, not exdusively by a single segment, a lesion in one segment or spinał nerve root usually causes weakness (paresis) of the affected muscle ratherthan complete paralysis (plegia). Slight weakness may also be noted in musdes that receive some inner-vation from the affected segment but are not principally supplied by it. The indicator musdes in the upper and lower limbs are listed in the ta-bles below. Whereas sensory (dorsal) root lesions may occur in isolation, motor (ventral) root lesions usually occur in association with dorsal root lesions, and therefore the dermatomes are also listed in the tables. Notę: Because these nerves of the trunk are derived directly from the spinał nerve roots without any intervening plexuses, the pattern of seg-mental innen/ation in the trunk is identical to the pattern of peripheral innervation.

Location of pain	Lateral and posterior side	Dorsoradial upper arm,	Posterior side of upper arm,	Ulnarace stwh
or sensory	of shoulder, anterolateral	radial forearm	extensor side of forearm	to
disturbance	side of proximal forearm	—* thumb	—♦ second/third (fourth) finger
Indicator muscle	© Deltoid	© Biceps brachii	© Triceps brachii, hand and	------ , J
(and other	© (Biceps brachii)	© (Brachioradialis)	digital flexors and extensors	fleios i
affected musdes)			© Thenar musdes	(TriGeasta^^H
			© Pectoralis major (atrophy of	~ąor-£OHM
Reflexes abolished			stemocostal part)
by a segmental	Biceps reflex	Biceps reflex	Triceps refłex	Trfcss - =fer
lesion	(Brachioradialis ref!ex)	(Brachioradialis refłex)	(Trómner reflex)	(TtoMni^H