Cervicogenic Mechanisms of Orofacial Pain and Headaches

Key Points

Structures of the cervical spine can give rise to orofacial pain and headaches.

A screening examination of the cervical spine is recommended in case of coexisting neck pain or when orofacial pain is triggered by head and neck movements.

Clinical tests are sufficiently valid for a first screening.

Specific and individualized interventions consisting of postural correction, therapeutic exercise, and manual therapy can assist the clinician in effectively managing cervical factors to reduce pain, restore function, and prevent recurrence of complaints.

Referral is recommended when cervical spine involvement is suspected.

Disorders of the musculoskeletal structures of the cervical spine can contribute to orofacial pain and headaches, separate from or in addition to temporomandibular disorders (TMDs). The clinician should be able to distinguish different types of neck pain, understand the mechanisms of referred pain from the cervical spine, perform a screening evaluation, and initiate appropriate referral for further evaluation and comprehensive management.

Cervical spine disorders (CSDs) encompass a number of disorders involving the muscles, facet joints, discs, and nerves of the cervical spine. The most common symptoms are pain and functional limitations, which vary with physical activity and/or static positioning. Subclassification of CSDs includes an extensive list of diagnostic terms, such as cervicalgia, cervical sprain/strain, discogenic disease, and facet syndrome.¹ In the absence of pathology or systemic disease, objective diagnosis of the cause of cervical pain is often difficult. Recently, the Task Force on Neck Pain proposed a New Classification System for Neck Pain, which may facilitate communication among health care professionals² (Box 9-1).This classification system is used to classify the subset of individuals who seek clinical care for neck pain. It differs from earlier classification systems for neck pain and low back pain,^4,5 in that the decision for further assessment and treatment depends not only on the signs of pathology but also on the presence of disability. In this chapter, some questionnaires to rate the level of disability related to neck pain are introduced. Moreover, common CSDs that can cause pain in the orofacial region or in the head are presented. In the description of these CSDs, the authors indicate what type of headache/orofacial pain may be associated with the various CSDs. In addition, the codes from The International Classification of Diseases, Tenth (ICD-10) and Ninth (ICD-9) Editions are presented for each CSD.

Epidemiology of CSDs

Most people will experience some neck pain in their lifetimes, although for the majority, neck pain will not seriously interfere with daily activities.² One-year prevalence estimates of neck pain range from 30% to 50% in the general population, while 1-year incidence estimates of neck pain with associated disability range from 2% to 14%.² The prevalence of neck pain increases with age up to the fifth decade (and then decreases) and is higher among women than men.^2,6 Between 50% and 85% of those who experience neck pain at some point will report neck pain again 1 to 5 years later.^7–9 The experience of psychologic stress, prolonged forward head posture, and repetitive cervical movements increase the risk for developing neck pain.^10–12 The influence of repetitive movements and sustained head positions is reflected in high prevalence numbers of neck pain in specific populations, such as dentists,^13,14 professional drivers,¹⁵ and adolescents with prolonged computer use.¹⁶

Relationship Between Temporomandibular and Cervical Spine Structures

Many studies have reported the coexistence of TMDs and CSD symptoms.^17–19 The prevalence estimates of CSDs in TMD patients range from 23% to 70%, compared with 5% to 31% in control groups.^19–21 In some cases, comorbidity of TMDs and CSDs may be a symptom of a more generalized musculoskeletal disorder. Studies have reported that a variety of chronic disorders, like fibromyalgia (FM), chronic fatigue syndrome, and TMDs, commonly coexist.^22–25 For example, 70% to 75% of patients with FM met TMD criteria.²⁶ It is clear that these disorders frequently co-occur and share key symptoms.²⁵

The following theories postulate how CSDs may be a predisposing, precipitating, or perpetuating factor in orofacial pain or headaches.

Biomechanical interplay between head and neck structures

The cranium and the mandible both have muscular and ligamental attachments to the cervical area, forming a functional system called the craniocervical mandibular or stomatognathic system. Because of this close functional coupling, changes in the activity of the neck muscles and head position influence the activity of the masticatory muscles and jaw function and vice versa.^27–31 When the mandible is at rest, its position is determined by the viscoelasticity of the muscles and the postural muscle tone acting on the mandible.²⁸ With an upright head position, the relaxed mandible maintains a fairly constant distance from the maxilla of approximately 2 to 5 mm.³² With the head in a more forward posture, the mandible is slightly elevated.³³

Besides static changes in mandibular rest position and masticatory muscle activity, a dynamic interplay between structures of the head, neck, and mandible has been shown. For example, a kinesiographic study showed that when the head is held in a forward position, the mandible traverses an open-close movement path that is posterior to its path with the head in a natural position, and the condyles are pulled slightly downward.³⁴ Others have shown that open-close mandibular movements, as during eating, are accompanied by respective extension and flexion of the head^30,35 and that several neck muscles are coactivated during jaw clenching.^31,36

As a result of these synergistic relationships between the structures of the masticatory system and the neck, and the coexistence of TMDs and CSDs, poor head posture (mostly a forward head posture) and overload of the cervical spinal musculature have been suggested as etiologic factors for TMDs.^37,38 Clinical studies regarding such relationships, however, show contradictory results.³⁹ Even though some authors have reported small differences in head posture between TMD patients and healthy controls, the clinical relevance of these differences has been disputed.⁴⁰ Yet other studies did not find differences in head posture between TMD patients and controls.^41,42 So even though there is vast evidence showing the functional coupling between the musculoskeletal structures of the cervical spine and the masticatory system, there is only weak evidence for a direct biomechanical mechanism (such as the effect of poor head posture on the masticatory system) as a cause for TMDs.^39,43

Convergence and sensitization of cervical and trigeminal neurons

Convergence by multiple sensory nerves (cervical spinal nerves C1 to C4 and the trigeminal nerve) carrying input to the trigeminal spinal nuclei from various tissues of the head and neck is the neuroanatomical basis for referred pain. This was nicely demonstrated in an experimental study in which glutamate-evoked pain in the splenius muscle frequently caused referral of pain to the temporal region.⁴⁴ Interestingly, in the same study, when glutamate was injected into the masseter muscle, no referral of pain to the neck region was observed. However, other studies have provided evidence for a bidirectional relationship in convergence of muscle afferents from the trigeminal and upper cervical neural systems.^45–47 In addition, masticatory muscle pain has been shown to modulate the function of the cervical motor system and vice versa.⁴⁸ Even though the bidirectional relationship is not yet well understood, these findings may partly explain the manifestations of pain referral between these two areas.

Sensitization of the nervous system occurs when persistent nociceptive facilitation exceeds its inhibitory capacity. In this situation, a spectrum of neuroplastic changes, such as lowered nerve thresholds, enlarged receptive fields, and changed gene expression, occurs. Patients may have allodynia (experience of pain by stimuli that normally would not be perceived as painful) and hyperalgesia (exaggerated pain responses to mildly painful stimuli). For more details regarding the neurophysiologic relationship between the structures of the head and neck, see chapter 1.

Innervation of the cervical spine

Knowledge of the innervation of the various structures of the cervical spine is required to understand the neurophysiologic relationship between the structures of the head and neck. Also, understanding the referral patterns and characteristics of pain and dysfunction can provide the clinician and physical therapist with the means by which to determine which structure is causing the pain.

The cervical spine comprises the suboccipital and mid-lower cervical sections.The suboccipital section is considered the switching station for all afferent and efferent transmission to the cranium and orofacial region. The first three spinal nerves (C1 to C3) mediate pain at the suboccipital part of the cervical spine and may refer pain to the craniofacial region. These nerves innervate the ligaments and joints of the upper cervical spine; the anterior, posterior, and lateral suboccipital muscles; and the sternocleidomastoid (SCM) and upper trapezius muscles. They also innervate the posterior dura mater, tentorium and falx cerebelli, vertebral arteries, and the lateral walls of the posterior cranial fossa.⁴⁹

At the base of the occiput, the foramen magnum contains the meningeal branches of C1 to C3, the vertebral and spinal arteries, and the spinal components of the spinal accessory nerve. The posterior cranial fossa contains the confluence of sinuses, the roots of the fifth to twefth cranial nerves, the first two cervical nerves via the hypoglossal canal, the branches of C2 to C3 through the foramen magnum, and the ascending branches of C1 to C3, thus comprising several potential pathways for cervicogenic referral to the craniofacial region.^50–52 The greater occipital nerve branches off from the C2 dorsal root ganglia and thus may represent a source for occipital pain with or without retro-orbital referral. Suboccipital spinal neurons have been shown to be excited by ipsilateral vagal input and correspond to dermatomal receptive fields of upper cervical segments. They may represent another referral mechanism to the neck and jaw.^53,54

The spinal accessory nerve, which arises from the C2 to C4 levels, innervates the SCM and upper trapezius muscles, both of which commonly refer pain to the craniofacial region. Spinal accessory fibers also cross the midline, providing implications for contralateral or bilateral headache.^55–57 Another possible source of headache is transmitted via the C1 to C3 sinuvertebral nerves, which innervate the cranial membranes, dura mater of the posterior cranial fossa, and epidural vasculature.⁵⁸

The examples of biomechanical and neurophysiologic interplay between the structures of the head and neck illustrate that CSDs may influence pain in the orofacial region. Therefore, the cervical spine needs to be considered in the assessment of patients with orofacial pain complaints.⁵⁹

Screening of the Cervical Spine

As described in Box 9-1, the Task Force on Neck Pain introduced a four-grade classification system of neck pain severity. Because few major differences were found between trauma-related neck pain and neck pain with a nontraumatic etiology, the classification is recommended for all individuals who seek clinical care.² To use the classification system, information is needed on serious pathology, disability, and signs of nerve compression.

Serious pathology

For patients without exposure to blunt trauma, the Task Force on Neck Pain suggests to rule out serious pathology based on existing recommendations for the lumbar spine^2,60 (Box 9-2). The presence of such red flags should prompt the clinician to seek additional evaluation and care for such patients. A description of screening protocols for neck pain patients seeking emergency medical care is beyond the scope of this chapter. For an overview, see the Canadian C-Spine and the NEXUS protocols.⁶¹

Disability

Several reliable and valid self-assessment questionnaires are available to determine the level of disability in neck pain patients, including the Neck Disability Index⁶² and the Neck Bournemouth Questionnaire.⁶³ Within this framework, the Graded Chronic Pain Scale (GCPS)⁶⁴ is of special interest, because it is a universal system that can be used for any pain condition (like neck pain, headache, or temporomandibular pain), it is easy to use, and it is the most commonly used system to rate disability in scientific publications on TMD patients. In this system, GCPS grades 3 and 4 represent patients with high disability. According to the Task Force on Neck Pain, patients experiencing such pain-related disability require further assessment and treatment to prevent long-term disability (see Box 9-1).

Signs of nerve compression

Patients with neck pain that radiates to the arm can be suspected of a cervical radiculopathy. This is caused by an irritation of the cervical nerve root, mostly due to compression. In typical cases, the irradiating pain closely follows the area innervated by the affected nerve root. When a cervical radiculopathy is suspected, manual provocation tests that involve elongation of the nerves to elicit a pain response are recommended.⁶⁵ These diagnostic procedures have high predictive value when compared to gold standards of nerve conduction/magnetic resonance imaging and myelography.² Examples are the Spurling test, traction/neck distraction, the Valsalva maneuver, and the upper limb tension test. When consistent with the history and other physical findings, a positive Spurling test, as well as positive findings for traction/ neck distraction, and the Valsalva maneuver might be suggestive of a cervical radiculopathy (ie, given their high specificity). On the other hand, a negative upper limb tension test is highly suggestive of the absence of cervical radiculopathy, given its high sensitivity. A summary of the testing procedures is presented in Table 9-1. In the absence of acute trauma and symptoms of serious pathology, there is no evidence to support the use of diagnostic procedures such as routine imaging, anesthetic facet or medial branch blocks, or surface electromyography (EMG) for the diagnosis of radiculopathy.²

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