Neural Basis of Etiopathogenesis and Treatment of Cervicogenic Orofacial Pain

(1) Background and Objectives: The aim of this narrative review was to analyze the neuroanatomical and neurophysiological basis of cervicogenic pain in cervico-cranial pain syndromes, focusing particularly on cervico-orofacial syndromes as a background for the proper diagnosis and non-surgical treatment. Relevant literature on the topic from past 120 years has been surveyed. (2) Material and Methods: We surveyed all original papers, reviews, or short communications published in the English, Spanish, Czech or Slovak languages from 1900 to 2020 in major journals. (3) Results: The cervicogenic headache originates from the spinal trigeminal nucleus where axons from the C₁–C₃ cervical spinal nerves and three branches of the trigeminal nerve converge (trigeminocervical convergence) at the interneurons that mediate cranio-cervical nociceptive interactions. The role of the temporomandibular joint in the broad clinical picture is also important. Despite abundant available experimental and clinical data, cervicogenic orofacial pain may be challenging to diagnose and treat. Crucial non-surgical therapeutic approach is the orthopedic manual therapy focused on correction of body posture, proper alignment of cervical vertebra and restoration of normal function of temporomandibular joint and occlusion. In addition, two novel concepts for the functional synthesis of cervico-cranial interactions are the tricentric concept of mouth sensorimotor control and the concept of a cervicogenic origin of bruxism. (4) Conclusions: Understanding the basis of neuroanatomical and neurophysiological neuromuscular relations enables an effective therapeutic approach based principally on orthopedic manual and dental occlusal treatment.

Changes in deep neck muscle length from the neutral to forward head posture. A cadaveric study using Thiel cadavers

Forward head posture (FHP) is one of the most common postural deviations. Deep neck muscle imbalance of individuals with FHP is of primary concern in clinical rehabilitation. However, there is scarce quantitative research on changes in deep neck muscle length with the head moving forward. This study aimed to investigate changes in deep neck muscle length with different severity levels of FHP. Six Thiel‐embalmed cadavers (four males and two females) were dissected, and 16 deep neck muscles in each cadaver were modeled by a MicroScribe 3D Digitizer in the neutral head posture, slight FHP, and severe FHP. The craniovertebral angle was used to evaluate the degrees of FHP. Quantitative length change of the deep neck muscles was analyzed using Rhinoceros 3D. In slight FHP significant changes in length occurred in four muscles: two shortened (upper semispinalis capitis, rectus capitis posterior minor) and two lengthened (longus capitis, splenius cervicis). In severe FHP all occipital extensors were significantly shortened (10.6 ± 6.4%), except for obliquus capitis superior, and all cervical extensors were significantly lengthened (4.8 ± 3.4%), while longus capitis (occipital flexor) and the superior oblique part of the longus colli (cervical flexor) were lengthened by 8.8 ± 3.8% and 4.2 ± 3.1%, respectively. No significant length change was observed for the axial rotator. This study presents an alternate anatomical insight into the clinical rehabilitation of FHP. Six muscles appear to be important in restoring optimal head posture, with improvements in FHP being related to interventions associated with the occipital and cervical extensors.

Assessment of potential strain injury to rectus capitis posterior minor muscles during whiplash type distortions of the cervical spine

CONTEXT

Whiplash type injuries resulting from a rear end motor vehicle accident (REMVA) are thought to be caused by excessive loading and displacement of structural components of the cervical spine. On impact, the seat propels the driver's torso forward relative to the head, resulting in forced flexion of the occipitoatlantal (OA) joint, accompanied by forced stretching of the rectus capitis posterior minor (RCPm) muscles. Flexion of the OA joint and stretching of the RCPm muscles continues to increase until the vehicle's headrest strikes the back of the driver's head. It is known that externally applied forces that attempt to move the OA joint beyond its anatomic barrier can result in fracture, dislocation, or soft tissue damage to its structural components. However, the magnitude of headrest backset, defined as the distance between the driver's head and the vehicle's headrest, that would result in RCPm muscles being stretched to a length that would put them at risk for a muscle strain injury is unknown.

OBJECTIVES

To quantify the relationships among flexion of the OA joint, RCPm muscle stretch, and backset, and to quantify the biomechanical response of RCPm muscles to increasing levels of axial load due to stretching.

METHODS

Unembalmed head and neck specimens from three White females aged 85, 63, and 70 years were obtained from the Anatomical Services Division at the University of Maryland. Donors had provided written consent allowing use of their body for research purposes. Using an analytic model of the OA joint, the relationships between flexion of the OA joint and RCPm muscle stretch as a function of backset were estimated. RCPm muscles were removed from the cadavers and forcibly stretched using a servomechanism controlled hydraulic testing machine to quantify the load/displacement properties. After testing, the tissues were sectioned, mounted, and stained using Masson's trichrome to selectively stain muscle fibers red and collagen blue.

RESULTS

Forced flexion of the OA joint was seen to be directly related to the magnitude of headrest backset. For values of backset greater than 7.2 cm, biomechanical testing of the RCPm muscles revealed that strain injuries ranged from the tearing of a few muscle fibers to complete rupture of the muscle and separation of the tendon at the posterior process of C1.

CONCLUSIONS

Results showed that headrest backset at the time of vehicle impact is an important factor in estimating the risk of muscle strain injury to RCPm muscles. Muscle strain injury would be expected to impact the functional relationship between the RCPm muscles and the pain sensitive spinal dura. Physicians should be alert to the possibility that cervicogenic pain patients who have experienced whiplash associated with REMVA may show clinically relevant structural damage to the RCPm muscles on MRI.

Effects of sitting posture and jaw clenching on neck and trunk muscle activities during typing

Neck pain is one of the most common musculoskeletal complaints. Evidence suggests that increased activities of neck and trunk muscles are one of the mechanisms related to neck pain. Jaw clenching and sitting posture may modulate the muscle activity in neck and trunk muscles during typing. The present study aimed to assess the effects of different postural positions and clenching conditions on neck and trunk muscle activities. Thirteen healthy adults (39.8 ± 5.0 years) performed computer typing tasks in four conditions (two postural positions [upright vs slouched] and two jaw clenching conditions [clenching vs non-clenching]). Integrated surface electromyography (iEMG) was measured in sternocleidomastoid (SCM), upper trapezius (uTP) and middle trapezius (mTP) muscles and compared between conditions. The Friedman and Wilcoxon signed-rank tests with Bonferroni's corrections were used to estimate the condition-specific differences in the iEMG data. The statistical significance level was set at 5%. In both postural positions, iEMG_SCM was significantly greater under the jaw clenching than under the non-clenching condition (χ²  = 21.700, P < .01). Under both jaw clenching conditions, iEMG_uTP was significantly greater in the slouched than in the upright postural position (χ²  = 23.182, P < .01). No significant differences in iEMG_mTP were seen across conditions (χ²  = 5.018, P = .10). Sitting posture and jaw clenching appear to influence activities of different muscles.

Implied Evidence of the Functional Role of the Rectus Capitis Posterior Muscles

Context

Osteopathic physicians often target the rectus capitis posterior minor (RCPm) and rectus capitis posterior major (RCPM) muscles when using muscle energy or soft tissue cervical techniques to treat patients with head and neck pain. The RCPm and RCPM muscles are located deep within the posterior occipitoatlantal and atlantoaxial interspaces, respectively.

Objective

To characterize the functional role of RCPm and RCPM muscles by comparing electromyographic (EMG) activation patterns of these muscles with EMG activation patterns of specific flexor and extensor muscles of the head and neck, the sternocleidomastoid (SCM), and the splenius capitis (SC) muscles, respectively.

Methods

Asymptomatic participants were recruited from the Michigan State University College of Osteopathic Medicine student body. Disposable 25-gauge, bipolar fine-wire intramuscular electrodes were used to collect EMG data from the right and left RCPm and RCPM muscles. Surface electrodes were used to collect EMG data from the right and left SCM and SC muscles. Data were collected as participants performed 4 cycles of flexion and extension with an external 4-lb force applied to the back of the head and the forehead.

Results

In RCPM muscles, EMG activity was significantly greater (P<.003) during flexion and extension of the head and neck when an external force was applied to the back of the head. EMG activity in SCM muscles was significantly greater (P<.0001) during flexion and extension of the head and neck when an external force was applied to the forehead. The authors observed that EMG activity in SC muscles was significantly greater (P<.015) during flexion and extension of the head and neck when an external force was applied to the back of the head. No significant difference was found in EMG activity in RCPm muscles (P<.834) during flexion and extension of the head and neck, regardless of whether the external force was applied to the back of the head or the forehead.

Conclusion

The EMG activation patterns of the RCPm muscles suggest that their functional role may be to stabilize the occipitoatlantal joint by helping maintain congruency of the joint surfaces. In contrast, the EMG activation patterns of the RCPM muscles suggest that their functional role may be to contribute to extension of the head, primarily at the occipitoatlantal and the atlantoaxial joints.

Osteopathic Manipulative Therapy in Patients With Chronic Tension-Type Headache: A Pilot Study

CONTEXT

Nonpharmacologic treatment, such as osteopathic manipulative therapy (OMTh; manipulative care provided by foreign-trained osteopaths) may be a beneficial complementary treatment for tension-type headache. However, to the authors' knowledge, the benefit of OMTh in the management of tension-type headache has not been explored, especially chronic tension-type headache (CTTH).

OBJECTIVE

To investigate the effectiveness of OMTh compared with traditional treatment in reducing pain intensity, frequency, and duration of CTTH, and to evaluate the objective postural measurement of the forward head posture (FHP) as an integral parameter in the assessment of the effects of OMTh and traditional management of CTTH.

METHODS

Patients with CTTH were registered at the Headache Centre of Trieste in Italy. At the time of the study, none of the patients had been taking any headache prophylaxis in the past 3 months. A 3-month baseline period was recorded by all patients with an ad hoc diary. Patients were randomly placed in the test or control group using a simple randomization program in Excel (Microsoft). Patients in the OMTh group underwent a 3-month period of OMTh, and patients in the control group were treated with amitriptyline. Pain intensity, frequency, and duration of headaches, as well as FHP were analyzed.

RESULTS

The study enrolled 10 patients (mean [SD] age, 42.6 [15.2] years) in the OMTh group and 10 patients (51.4 [17.3] years) in the control group. The final assessment of OMTh patients showed statistically significant changes in all headache parameters: pain intensity decreased from a mean (SD) score of 4.9 (1.4) to 3.1 (1.1) (P=.002); frequency decreased from 19.8 (6) to 8.3 (6.2) days per month (P=.002); and the duration of headaches decreased from 10 (4.2) to 6 (3) hours (P=.01). Significant improvement of all parameters was found in the control group as well: pain intensity decreased from a mean (SD) score of 5.9 (0.7) to 4.2 (1.75) (P=.03); frequency decreased from 23.4 (7.2) to 7.4 (8.7) days per month (P=.003); and duration decreased from 7.8 (2.9) to 3.6 (2.1) hours (P=.002). Forward head posture significantly improved in OMTh patients (P=.003).

CONCLUSIONS

Our data suggested that OMTh may be an effective treatment to improve headaches in patients with CTTH. Our results also suggest that OMTh may reduce FHP.