Splenius Capitis Muscle Syndrome
This article describes a very painful and commonly occurring pain syndrome associated with the splenius capitis muscle insertion. This syndrome was first described in the 1980’s by this author. The onset of pain is often caused by motor vehicular trauma, blunt trauma, falls, and, in particular, postural situations where superior and inferior lateral oblique movements of the head on the neck occur. This type of excessive repetitive movement can cause an overuse injury where small focal, degenerative changes in the insertion fibers can occur. This is, in practical terms, similar to the histopathologic process of insertion tendinosis seen at other narrow bony processes. Bony processes include the mandibular coronoid process tip,1 and the greater cornu of the hyoid bone,2 as described by this author in other articles demonstrating photomicroscopic evidence of degenerative change in insertion fibers.
Gray3 describes the origin of the splenius capitis muscle to begin on the spinous processes of vertebrae from C-7 to T-3 and the ligamentum nuchae. The insertion extends from the medial edge of the mastoid process and the lateral part of the superior nuchal line. Dissection of the insertion area shows the splenius capitis lying under the triangle formed by the trapezius and sternocleidomastoid muscles (see Figure 1). The nerve supply to the splenius capitis is provided by lateral branches of the posterior rami of the middle and lower cervical spinal nerves.
Bilaterally, the splenius capitis muscles extend and hyper-extend the head and neck. However, acting unilaterally, the muscle flexes and rotates the head and neck to the same side; particularly in the superior and inferior lateral oblique movements. The muscle can be felt to tighten in the mandibular protrusive movement and in the wide opening movement of the lower jaw. The dynamic relationship of the cranio-cervico-mandibular-hyoid musculature is perhaps one of the most complex inter-relationships of muscle groups in the human body.
Splenius Capitis Muscle Syndrome typically mimics the respective pain reference patterns of temporal tendinitis and migraine headache. The painful headache starts at the lateral margin of the superior nuchal line and medial to the mastoid process. The reference areas of pain are described as follows (see Figure 2):
- Rear of head aches and hurts.
- Lateral temple headache.
- Retro-orbital headache and pressure.
- Aching pain above the eye.
- Aching pain at cheekbone under eye.
- Eye hurts and is sensitive to bright light.
- Pain radiating to neck, shoulder and arm at times.
- Nausea and vomiting when pain is intense.
The test to determine if the pain complex is primarily a muscular rather than a primary sensory nerve problem utilizes the effect of local anesthetic infiltration in the insertion area of the splenius capitis muscle. A local anesthetic infiltration in the muscle should not create a defined region of sensory loss at the scalp. If a clinician blocks the greater occipital nerve,4-5 the block would cause a defined geographic area of anesthesia on the scalp. Similarily, a block of the lesser occipital nerve would cause a defined region of scalp anesthesia lateral to the greater occipital pattern of sensory distribution.
Again, a block of the insertion fibers of the splenius capitis muscle6 (see Figure 3) does not cause a numbness of the scalp as does a block of the greater or lesser occipital nerves.
Confirming Diagnosis And Treatment
The most effective way to confirm the diagnosis of Splenius Capitis Muscle Syndrome is to put digital pressure at the superior nuchal line between the trapezius and sternocleidomastoid mucles at the nuchal line. If the area is painful and/or stimulates the pain referral pattern, then the source of the headache and pain may have been located. Next, inject one cc of a non-vasoconstrictor local anesthetic into the painful insertion zone, first aspirating to assure that the needle tip is not in a vessel. Then slowly inject 0.8 cc local anesthetic (see Figure 3). Within one minute the pain pattern should be remitted if the diagnosis is correct and if there are no other concurrent pain disorders present. With the pain remitted, inject a 1/8 to 1/4 cc of cortisone into the area. Hopefully, the pain will not return. However, if it does, repeat the process two or three times. This will help to determine if the insertion fibers are damaged and may require radiofrequency thermoneurolysis (RFTN) to “turn off” the terminal sensory nerve end organs.
If radiofrequency thermoneurolysis is indicated, an RFTN unit, such as the Owl RF Generator Model URF-2AP (Canadian Medical Devices, Toronto, Canada), is utilized. A typical technique is to create three RFTN heat lesions (see Figure 4) on a horizontal axis to try to assure “coverage” of the damaged insertion fibers. Prior to lesioning, use the stimulus mode of the RF Generator to assure the probe tip is not on an unexpected motor or sensory nerve branch. The RFTN should not create any sensory deficit at the scalp since the local anesthetic block did not do so.
This syndrome typically produces pain in the face, temple and cheek area, thus a diagnostic work up may need to include the pain management dentist as well as the pain management physician. The differential diagnosis of headache may be simple to make at times. However, the diagnostic effort may be confounded by a more complex condition presented by the patient. In the more complex situation, referral and more advanced testing may be required. An example is the possible need for a cervical facet joint block with local anesthetic. A neurosurgeon7 or anesthesiologist would be needed for a facet block to assist in the diagnosis of headache and referred pain to the cheekbone and temple emanating from cervical facet joint disease. The complex pain patient may present with one or more facial pain syndromes,8 a temporomandibular joint injury or neuralgia, and/or other cervical pain syndromes as well. This type of patient may have great difficulty in receiving comprehensive care in the absence of a multidisciplinary team environment.
This article has described the anatomical region of the insertion zone of the splenius capitis muscle, its function, distribution of the pain pattern, differential diagnosis, methods of testing, and treatment.
When repeated cortisone injections fail to provide relief, the author has found that surgical management of the pain utilizing radiofrequency thermoneurolysis is a safe and proven pain management tool.9-10