The cervical spine and associated muscular support of the head interwoven with vessels and nerve supply in the head and upper extremities, compose a complex structure with many sites for the generation of pain. A reduction in the space in which nerves pa ss through or lie can result in pain and loss of function. If the pressure is acute, pain is more likely to occur. Loss of function is generally the result of more prolonged and continuous pressure.
The sites of nerve compression in the neck are the intervertebral foramina, the spinal canal, the interscalene space and the course of the occipital nerves through the trapezius muscle at the base of the skull. Impairment or free movement at the joints, discs or ligaments may lead to irritation of sensitive structures of the joints and soft tissue of the neck. Reflex muscle spasms resulting from this irritation can produce continuous tension on the periosteal insertion of muscles. It is common for head and neck pain to originate with stress on the cervical musculature. Tension headaches are the result of sustained muscle contraction which produces both irritation at muscle insertion points and ischemic pain of the muscle itself.
Irritation of the cervical nerve roots at any point from their origin of the spinal cord to their paths to the occipital muscles can result in pain referred to the head and neck or upper extremity. Common sources of such irritation are the degenerative changes associated with osteophytes. As the degenerative process progresses, the spinal canal decreases in all diameters causing pressure on the long ascending and descending tracts as well as the cervical nerve roots. The most frequent complaint of the patient with cervical spondylosis is cervical, occipital or atypical facial pain due to irritation of the C2, C3 and C4 nerve roots. The continued irritation of these roots as they exit from the intervertebral foramina produce an inflammatory response i n the root with secondary edema.
As the greater and lesser occipital nerves pierce the trapezius at the base of the skull they are subject to pressure by cervical muscles and spasm. The result, an occipital neuralgia, produces further cervical spasms leading to a reflex perpetuation of occipital pain. Carcinoma and tumor invasion of the cervical spine and soft tissues of the neck may cause destruction as well as encroachment in cervical nerve roots or invasion of branches of the cervical plexus. These malignant forms of cervicogenic headache will not be discussed.
The purpose of this discussion is to describe those injection techniques that have been found useful in the treatment of muscle tension and cervicogenic headaches. These procedures include: trigger point injections, occipital nerve blocks, anesthetic blocks of the cervical nerve C2-C5, facet joint blocks at C2, C3 and cervical epidural steroid injections.
To understand how a blockade of the occipital nerve is efficacious in the treatment of headache, a review of the anatomy will be presented. The greater and lesser occipital nerves are sensory nerve which enter into the second, and to some extent the thir d cervical segments. The nerves enter the spinal cord via the Tract of Lissauer to terminate in the substantia gelatenosa of the upper cervical cord where they synapse. The infratentorial intracranial structures are innervated by the upper three cervical nerves. Sensory cutaneous distribution in the occipital nerve is over the back of the head anteriorly to the borders of the innervation of the first division of the trigeminal nerve. The C2 component is a more medial band extending form the superior nuch al line to this boundary. C1, when present, innervates an overlapping area more posteriorly. The greater occipital nerve passes over the superior nuchal line midway between the mastoid process on the occipital protuberance just lateral to the insertion of the nuchal ligaments. The lesser occipital protuberance is just lateal to the insertion of the nuchal ligaments. The lesser occipital nerve passes laterally to the greater occipital nerve over the nuchal ridge.
The greater occipital nerve runs transversely and then turns at right angles to run posteriorly. It then emerges through the aperture above the aponeurotic sling between the trapezius and the sternomastoid. This fact renders untenable any speculation t hat it may be compressed by spasm in the trapezius. Similarly, the nerve is not vulnerable to bony compression between the posterior arch of the atlas and the lamina of the axis. How the occipital nerve becomes sensitive to the diverse headache condition described is still a matter of speculation.
Occipital nerve blockade has been used for the treatment of diverse headaches for decades. The most effective position for greater occipital blockade is sitting or lateral decubitus with the chin flexed upon the chest. A short 25 gauge needle is inserted through the skin at the level of the superior nuchal line so as to develop a wall of local anesthetic surrounding the posterior occipital artery. The procedure should be done under strict aseptic conditions. The artery is commonly found approximately one-third of the distance between the external occipital protuberance and the mastoid process on the superior nuchal line. Injection of 3-5 ml of local anesthetic in this area with or without depo-corticosteroids will produce satisfactory anesthesia. Due to the superficial nature of this block complications are infrequent but may include hematoma, infection and paresthesia. Occipital nerve blockade will local anesthetic may also be used as a prognostic tool to determine if rhizotomy is warranted in refr actory cases. Occipital rhizotomy may be performed surgically or using a cryoprobe.
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