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Cervical Radicular Pain and Radiculopathy

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Definitions

Main article: Cervical Spine Pain Definitions

Cervical radiculopathy is characterised by objective loss of neurologic function. Loss of function is some combination of sensory loss, motor loss, or impaired reflexes, in a segmental distribution. Pain is not a component of radiculopathy, and so is distinguished from cervical radicular pain.[1]

Pathophysiology

Not much is known about the causes and mechanisms of cervical radicular pain. The literature often uses the term cervical radiculopathy, but radiculopathy and radicular pain are not synonymous.

Radiculopathy arises from either direct compression of a cervical spinal nerve or root, or by ischaemia from vascular injury to their blood supply. There is a conduction block along the affected axons which results in sensory or motor loss. Compression of axons, including those of the lumbar nerve roots, does not cause activity in nociceptive afferent fibres. Meanwhile, compression of a dorsal root ganglion does cause pain through activation of Aฮฒ and C fibres. The causes of cervical radicular pain cannot therefore be attributed to the same causes as those of radiculopathy.

It is thought that inflammation of the cervical nerve roots is the underlying mechanism through which radicular pain occurs secondary to disc herniation. There are pro-inflammatory molecules in disc material. Meanwhile, inflammation is not the cause of pain in other causes of radicular pain when due to tumours, cysts, and osteophytes. In these conditions it must be through dorsal root ganglion compression that pain occurs, as these conditions are non-inflammatory in nature.[1]

Aetiology

Clinical Features

The asterix indicates the only area where there is a statistical difference, with impaired in the distal radial aspect of the dorsal forearm more common in C6 than C7 radiculopathy. Based off data from Rainville et al. [2]

Cervical radiculopathy is characterised by negative objective signs: sensory loss, motor loss, or impaired reflexes, in a segmental distribution. The sensory loss occurs in the upper limbs, and tends to be dermatomal in distribution.[1] Notably however C6 and C7 cannot be differentiated based on dermatomes alone.[2]

The pattern of cervical radicular pain on the other hand is not dermatomal. The pain can be felt proximally in the scapula and shoulder girdle, and scapula pain usually precedes pain in the arm and/or fingers. This is analogous to the common finding of buttock pain with lumbar radicular syndrome. The reason it is not dermatomal is likely due to the pain not being restricted to cutaneous fibres, but there is also a deeper pain arising from the muscles and joints. The segmental innervation of the skin (dermatomes) is different to that of the deeper tissues. The muscles of the shoulder girdle are supplied by C6 and C7, very different to their dermatomes. And so the segmental innervation of muscles is more closely related to the radicular pain patterns than dermatomes, while dermatomes are more helpful for patterns of sensory loss in radiculopathy.[1][3]

(a)C5 and C8 cutaneous nerves traverse up and down the spine of the scapula, respectively, whereas the courses of C6 and C7 cutaneous nerves are not found. (b) The site of radicular pain involving the C6 root overlaps with that of the C5 root, and also involves the posterior deltoid.[3]

The site of scapula pain may be a helpful data point in determining the affected level in cervical radicular pain. Mizutamari et al suspect that scapula pain occurs through the medial branches of the dorsal rami of the cervical nerves. They found that there was no cutaneous course of C6 and C7 and that these patients complained of deep scapula pain only. This is compared to patients with C5 and C8 lesions having both superficial and deep pain.[3]

Mizutamari et al found the following pain referral pattern:
Nerve root Shoulder Girdle Region Deep or superficial
C5 Suprascapular region Superficial and deep pain
C6 Suprascapular to posterior deltoid region Deep pain
C7 Interscapular region Deep pain
C8 Interscapular and scapular regions Superficial and deep pain

References

  1. โ†‘ 1.0 1.1 1.2 1.3 Bogduk. The anatomy and pathophysiology of neck pain. Physical medicine and rehabilitation clinics of North America 2011. 22:367-82, vii. PMID: 21824580. DOI.
  2. โ†‘ 2.0 2.1 Rainville et al.. Exploration of sensory impairments associated with C6 and C7 radiculopathies. The spine journal : official journal of the North American Spine Society 2016. 16:49-54. PMID: 26253986. DOI.
  3. โ†‘ 3.0 3.1 3.2 Mizutamari et al.. Corresponding scapular pain with the nerve root involved in cervical radiculopathy. Journal of orthopaedic surgery (Hong Kong) 2010. 18:356-60. PMID: 21187551. DOI.

Literature Review

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