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Prolapsed intervertebral discs are most common between C4 and T1 in the cervical spine and between L3 and S1 in the lumbosacral spine. In the cervical region, there is not a great discrepancy between the level of the cervical spinal cord segment and the cervical vertebra of the same number, i.e. the C5 segment of spinal cord, the C5 nerve roots and the C4/5 intervertebral foramen, through which the C5 spinal nerve passes, are all at much the same level (see Fig. 6.1, p. 83). If the patient presents with a C5 neurological deficit, therefore, it is very likely that it will be a C4/5 intervertebral disc prolapse.

Figures 6.1 and 9.3 show that this is not the case in the lumbar region. The lower end of the spinal cord is at the level of the L1 vertebra. All the lumbar and sacral nerve roots have to descend

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Common nerve roots to be compressed by prolapsed intervertebral discs:

Vertebral body

Theca, i.e. spinal dura mater

Intervertebral

disc

Sacrum

Spinal cord

Lumbosacral nerve roots forming the cauda equina, in the subarachnoid space, within the theca

Spinal nerve, with dural sleeve, leaving the spinal canal via an intervertebral foramen

Fig. 9.3 Posterior view of the cauda equina. NB The pedicles, laminae and spinous processes of the vertebrae, and the posterior half of the theca, have been removed.

L2/3

L4/5/S1

L5/S1

L3/4

L4/5

S1/2

L2/3

S2

L4/5

S1

Knee jerk L3/4

(NB no jerk for L5)

Ankle jerk S1/2

Fig. 9.5 Segmental nerve supply to the lower limb, in terms of movements, tendon reflexes and skin sensation.

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Spinal tumours

Pain in the spine and nerve-root pain may indicate the presence of metastatic malignant disease in the spine. More occasionally, such pains may be due to a benign tumour such as a neurofibroma. The root pain may be either unilateral or bilateral. It is known as girdle pain when affecting the trunk, i.e. between T3 and L2. Segmental neurological signs in the form of lower motor neurone weakness, deep tendon reflex loss, and dermatome sensory abnormality may be evident, but the reason for early diagnosis and management is to prevent spinal cord compression, i.e. motor, sensory and sphincter loss below the level of the lesion (Chapter 6, see pp. 90–2).

Brachial and lumbosacral plexus lesions

Lesions of these two nerve plexuses are not common, so they will be dealt with briefly. Of the two, brachial plexus lesions are the more common. In both instances, pain is a common symptom, together with sensory, motor and deep tendon reflex loss in the affected limb.

Spinal nerves from C5 to T1 contribute to the brachial plexus, which runs from the lower cervical spine to the axilla, under the clavicle, and over the first rib and lung apex. Lesions of the brachial plexus are indicated in Fig. 9.6.

Spinal nerves from L2 to S2 form the lumbosacral plexus, which runs downwards in the region of the iliopsoas muscle, over the pelvic brim to the lateral wall of the pelvis. The common pathology to affect this plexus is malignant disease, especially gynaecological cancer in women.

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Peripheral nerve lesions

Individual peripheral nerves in the limbs may be damaged by any of five mechanisms.

1.Trauma: in wounds created by sharp objects such as knives or glass (e.g. median or ulnar nerve at the wrist), by inaccurate localization of intramuscular injections (e.g. sciatic nerve in the buttock), or by the trauma of bone fractures (e.g. radial nerve in association with a midshaft fracture of the humerus).

2.Acute compression: in which pressure from a hard object is exerted on a nerve. This may occur during sleep, anaesthesia or coma in which there is no change in the position of the body to relieve the compression (e.g. radial nerve compression against the posterior aspect of the humerus, common peroneal nerve against the lateral aspect of the neck of the fibula).

3.Iatrogenically: following prolonged tourniquet application (e.g. radial nerve in the arm), or as a result of an ill-fitting plaster cast (e.g. common peroneal nerve in the leg).

4.Chronic compression: so-called entrapment neuropathy, which occurs where nerves pass through confined spaces bounded by rigid anatomical structures, especially near to joints (e.g. ulnar nerve at the elbow or median nerve at the wrist).

5.As part of the clinical picture of multifocal neuropathy. There are some conditions that can produce discrete focal lesions in individual nerves, so that the patient presents with more than one nerve palsy either simultaneously or consecutively (e.g. leprosy, diabetes and vasculitis).

The speed and degree of recovery from injury or compression obviously depends on the state of the damaged nerve. No recovery will occur if the nerve is severed, unless it is painstakingly stitched together soon after injury by surgery. Damage which has injured the nerve sufficiently to cause axonal destruction will require regrowth of axons distally from the site of injury, a process which tends to be slow and incompletely efficient. Damage which has left the axons intact, and has only injured the myelin sheaths within the nerve, recovers well. Schwann cells reconstitute myelin quickly around intact axons.

Some peripheral nerve palsies are more common than others. Figures 9.7 and 9.8 show the common and uncommon nerve lesions in the upper and lower limbs, respectively. Brief notes about the uncommon nerve palsies are shown. The remainder of this chapter deals with the three common nerve palsies in the upper limbs and the two common ones in the legs.

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