Neck disorders are common and create a large burden on society. The burden to the healthcare system is more than 50 billion dollars each year.(1, 2) Additionally, neck related disorders can lead to a reduced ability or inability to work, and reduced work-related productivity.(3–5) Individuals with dysfunctions originating in the cervical spine can present with a large variety of symptomatic regions including: the neck, occipital and facial areas, shoulder, arm, and scapulothoracic region. Any structure in the neck including the intervertebral disc, ligaments, muscles, facet joints, dura, and nerve roots can contribute to the pain.(6, 7) Cervicogenic headache (CGH) is an example of a condition that is caused by dysfunction in the cervical spine. Cervicogenic headache has been defined by the International Headache Society as “pain, referred from a source in the neck and perceived in 1 or more regions in the head and/ or face”.(8) The prevalence of CGH has been reported to range from 15–20% of all headaches,(9) and around 4% of the general population experiences CGH’s.(10, 11) It typically presents as an unilateral headache that can spread to the frontal, temporal and orbital regions, neck, shoulder, and arm. Although the exact mechanism remains elusive, it appears that CGH is the result of mechanical dysfunction in the upper cervical spine.(11–13) A possible rationale for the development of CGH is the direct relationship between the trigeminal nerve and the spinal nerves C1 through C3 at the trigeminocervical nucleus.(14, 15) The trigeminocervical nucleus is functionally continuous with the dorsal horns of the upper cervical segments therefore nociceptive signals can converge with the trigeminal second order neuron. This could result in a perception of radiating pain via the ophthalmic branch of the trigeminal nerve.(14–16)
Another rationale for the development of CGH might be related to the fact that the motion of the suboccipital region is controlled by several groups of both smaller and larger muscle groups. It has been previously demonstrated that abnormal cervical functioning will change the proprioceptive awareness coming from mechanoreceptive neurons in this region.(17) There is an exceptionally high density of mechanoreceptors in the suboccipital muscles located in the posterior upper cervical region.(17) With cervical dysfunction, proprioception may be impeded as a result of pain, swelling, trauma, and/or muscular fatigue. In addition to this relationship between muscle and proprioception, Scali et al(18) and Pontel et al(19) demonstrated that fascial tissues originating from the Rectus Capitis Posterior Minor, Rectus Capitis Posterior Major, and the Obliquus Capitis Inferior can be identified in the space between the C1 and C2 vertebrae. These fascial tissue structures have been referred to as the “myodural bridges”. Between the arches of C1 and C2, the myodural bridges merge with the meningovertebral ligaments and crosses the epidural space, inserting into the posterior aspect of the dura mater. It has been proposed that these myodural bridges are meant to protect the cervical dura during motion and prevent compression of the cord.(18) The significance of the myodural bridge is that there is a direct anatomical connection between the muscle, cervical fascia, and the central nervous system. This could possibly explain the phenomenon of neurotension often identified by clinicians when treating patients with headaches and cervical related dysfunctions.(20–22)
Muscular impairment (dysfunctions) has been identified as possible contributing factor for the development of CGH.(23, 24) The upright position in humans results in loading of the cervical spine due to the weight of the head. This can leave the neck susceptible to progressive, degenerative changes over time. These changes will result in mechanical compression due to an increased cervical curve and a posterior rotation of the head on the neck. The ventral ramus of the upper cervical spine innervates the prevertebral muscles along with the facet capsules of C2 and C3.(25) The median atlantoaxial joint and its ligaments, the posterior cranial fossa and dura mater, the trapezius, and sternocleidomastoid (SCM) are supplied by C1-C3 nerves.(6, 25) Muscles will adapt to both the position they are placed in and the functions they have to perform. Patients with CGH often present with forward head posture that leads to an upper cross muscle syndrome (UCMS).(26) The upper cross muscle syndrome is characterized by the simultaneous development of both weak and short muscles. Weakness and endurance deficits in the deep neck flexor muscles have been identified in those with CGH. This may contribute to muscular imbalance and susceptibility to injury in the cervical region.(27) Within this UCMS, the sternocleidomastoid, upper trapezius, scaleni, and suboccipital muscle will present in a hypertonic state and shortened position.(23) The shortening and increased tone of the suboccipital muscles could result in prolonged neural tension through the myodural bridge. Prolonged muscle tone will lead to muscle dysfunctions such as trigger points. Trigger points are identified as a taut band within a muscle and have a characteristic "nodular" texture upon palpation.(28) When palpated, trigger points will elicit pain that can be felt locally or that can cause radiating pain.(29) Trigger points have been identified in those with CGH in the upper trapezius, SCM, erector spinae, and suboccipital muscles.(27, 30) Trigger points of the SCM can produce a unilateral referred pain over the forehead and around the ipsilateral eye and ear as seen in CGH.(31)
It has been demonstrated that CGH is caused by dysfunction of the upper cervical spine. Due the soft tissue connection between muscle, cervical fascia and dura, this region might contribute to the development of CGH’s. Therefore, it was the primary aim of this study to evaluate if subjects with CGH have concurrent neural tension signs. The secondary aim of this study was to investigate if there is a correlation between the position of atlas and mobility of atlantoaxial joint in those experiencing cervicogenic headaches compared to a healthy control group.