Numbness, pain, and/or weakness involving one or both arms are common reasons for referral to the neuromuscular clinician. These symptoms may be due to radiculopathy, brachial plexopathy, or one or more mononeuropathies. Some systemic etiologies for these focal neuropathic disorders have been discussed in preceding chapters (e.g., Lyme disease, vasculitis, and diabetes mellitus). This chapter will focus mainly on radiculopathies secondary to compression (e.g., degenerative joint disease and herniated discs), brachial plexitis, traumatic plexopathies, and focal mononeuropathies related to compression or entrapment. Before discussing the evaluation and management of these disorders, a review of the normal anatomy would be helpful.
Recall that there are seven cervical vertebrae, the first of which, the atlas, articulates with the skull's occipital condyles. The orientation of this joint allows primarily for flexion/extension movements. The second cervical vertebra, the axis, has a superiorly directed bony prominence, the dens, which articulates with the atlas and allows for rotational movements of the head and neck. The third through seventh cervical vertebrae are composed of the vertebral bodies themselves as well as short pedicles giving rise to laminae, which end in comparatively short and often bifid spinous processes. The transverse processes arise near the junctional zone of the pedicle and lamina. Between the transverse processes at each vertebral level lies a sulcus for the spinal nerves.
The spinal nerves are composed of a dorsal root and a ventral root (Fig. 23-1). The dorsal root consists of sensory fibers emanating from the dorsal root ganglia that lie outside the spinal cord. These dorsal root fibers enter the posterolateral aspect of the spinal cord and into the dorsal horn. Along the anterior aspect of the spinal cord, two or as many as 12 individual rootlets arising from anterior horn cells, fila radicularia, fuse to form the ventral root. Just distal to the dorsal root ganglion, the ventral and dorsal roots merge to form the spinal nerve. In the cervical region, there are eight cervical spinal roots on each side but only seven cervical vertebrae (Fig. 23-2). The first cervical spine nerve arises between the skull and atlas. As a result, each numbered cervical nerve root is related to the bony level immediately inferior to it down to the T1 vertebra. For example, the fifth cervical nerve root exits the spinal column just superior to the fifth cervical vertebrae. The eighth cervical nerve root exits the spinal column superior to the first thoracic vertebra.
The spinal cord is depicted with multiple ventral and dorsal rootlets joining to form the mixed spinal nerve root. Communications between the sympathetic ganglia and the spinal nerves are appreciated, and the gray and white rami are seen as well. (Reproduced with permission from Ferrante MA. Brachial plexopathies: classification, causes, and consequences. Muscle Nerve. 2004;30(5):547–568.)