Nerve compression signs

Neurologic signs include muscle wasting, motor weakness, sensory change, or a depressed tendon reflex. These are traditionally called nerve compression signs, though that is perhaps simplistic. Whatever the exact mechanism, they show that nerve function is compromised. Most low back problems affect a single nerve root, although they occasionally affect the same nerve root to both legs. Nerve function is usually only depressed because of overlap from adjacent roots. Complete anesthesia or paralysis is rare, so you must look for minor neurologic changes. You should check each

Table 2.2 The nerve supply of the L4-S1 nerve roots

L4

L5

S1

Distribution of pain

Anterior thigh

Dorsum of foot

Lateral border

and sensory disturbance

Great toe

of foot

Sole

Motor weakness

Quadriceps

Dorsiflexion ankle

Plantar flexion ankle

(Dorsiflexion

Eversion ankle

(Dorsiflexion

ankle)

Dorsiflexion toes"

great toe)

Reflex

Knee jerk

(Ankle jerk)

Ankle jerk

"An L5 lesion usually only affects some of these muscles.

"An L5 lesion usually only affects some of these muscles.

Figure 2.10 Clinical exam for motor weakness should test each myotome in turn, comparing the two legs for minor differences.

Figure 2.11 Clinical exam for sensory changes should test each dermatome in turn, comparing the two legs for minor differences.

dermatome and myotome in turn (Table 2.2) and the best way to detect minor change is to compare the two legs (Figs 2.10-2.12).

The common L5 and SI signs are weakness of the ankle and toes, sensory loss in the foot, and a diminished ankle reflex (Table 2.2). You should concentrate on these unless symptoms suggest a higher lumbar root or a widespread neurologic disorder.

The exact pattern of leg pain and a brief examination for nerve irritation and compression signs should usually allow you to diagnose a nerve root problem. Referred leg pain is simply part of more severe, but still "ordinary" backache.

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Back Pain Revealed

Back Pain Revealed

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