Immediate effects of the suboccipital muscle inhibition technique in craniocervical posture and greater occipital nerve mechanosensitivity in subjects with a history of orthodontia use: a randomized trial

ARTICLE INFORMATION Title: “IMMEDIATE EFFECTS OF THE SUBOCCIPITAL MUSCLE INHIBITION TECHNIQUE IN CRANIOCERVICAL POSTURE AND GREATER OCCIPITAL NERVE MECHANOSENSITIVITY IN SUBJECTS WITH A HISTORY OF ORTHODONTIA USE: A RANDOMIZED TRIAL” Running Head: SUBOCCIPITAL INHIBITION AND ORTHODONTICS Word Count: 3.361 words Number of figures: Four figures Number of tables: Two tables Practical Applications • There is a need for an in-depth review of the effect of the use of orthodontics on craniocervical posture • The Suboccipital Muscle Inhibition (SMI) technique has immediate effects on improving head posture in asymptomatic subjects. • Changes obtained in head position in sitting posture show a large clinical effect size. • The clinical significance of the augment of PPT of GO nerve after the SMI technique needs of further studies. Short Description: The objective of the study was to determine and analyze the differences in head posture and in the PPT of the GO nerve following an intervention by a SMI technique among asymptomatic subjects with a history of having used orthodontics AUTHORS INFORMATION: Author 1: Mr. Alberto M Heredia Rizo. Physiotherapist. Master Degree. Professor of Department of Physical Therapy. Faculty of Nursing, Physiotherapy, and Podiatry. University of Sevilla. Sevilla, Spain. Author 2: Mr. Ángel Oliva Pascual-Vaca. Physiotherapist. Osteopathic Physician. PhD. Professor of Department of Physical Therapy. Faculty of Nursing, Physiotherapy, and Podiatry. University of Sevilla. Sevilla, Spain. Author 3: Mr. Manuel Albornoz Cabello. Physiotherapist. PhD. Professor of Department of Physical Therapy. Faculty of Nursing, Physiotherapy, and Podiatry. University of Sevilla. Sevilla, Spain. Author 4: Mr. Cleofás Rodríguez Blanco. Physiotherapist. Osteopathic Physician. PhD. Professor of Department of Physical Therapy. Faculty of Nursing, Physiotherapy, and Podiatry. University of Sevilla. Sevilla, Spain. Author 5: Mr. Fernando Piña Pozo. Physiotherapist. Osteopathic Physician. Andalusian Health Service. Sevilla, Spain. Author 6: Mr. Antonio Luque Carrasco. Physiotherapist. Osteopathic Physician. Cesma Mutuality. Sevilla, Spain Corresponding Author: Alberto Marcos Heredia Rizo. Department of Physical Therapy. Faculty of Nursing, Physiotherapy, and Podiatry. University of Sevilla. Sevilla, Spain. C/ Avicena s/n 41009 Sevilla Tlf: (+34) 954 48 65 09 / (+34) 687 82 38 94 Fax: (+34) 954 48 65 27 Email: [email protected] ABSTRACT Objective: To identify and analyze the differences in craniocervical posture and pressurepain threshold of the greater occipital nerve in asymptomatic subjects with a history of having used orthodontics, after intervention by a suboccipital muscle inhibition technique. Material and Methods: Randomized, single blind, clinical study with a sample of 24 subjects (21 ± 1.78 years) divided into an experimental group (n = 12) who underwent the suboccipital muscle inhibition technique, and a control group (n = 12) who underwent a placebo intervention. We measured the sitting and standing craniovertebral angle and the pressure-pain threshold of the greater occipital nerve in both hemispheres. Results: The between-group comparison of the sample (Student's t and Welch's t) indicated that individuals subjected to the suboccipital muscle inhibition technique showed a statistically significant increase in the craniovertebral angle in both the sitting (P < 0.001, F(1,22) = 102.09, R² = 0.82) and the standing (P < 0.001, F (1,22) = 21.42, R² = 0.56) positions, and in the greater occipital nerve pressure-pain threshold in the non-dominant hemisphere (P = 0.014, F(1,22) = 7.06, R² = 0.24). There were no statistically significant differences observed for the greater occipital nerve mechanosensitivity in the dominant side (P = 0.202). Conclusion: Suboccipital muscle inhibition tecnhique improved the position of the head with the subject seated and standing, the clinical effect size being large in the former case. It also decreased slightly the greater occipital nerve's mechanosensitivity with statistical significance only in the non-dominant hemisphere, although the effect size was small. Key Indexing Terms: Complementary Therapies, Greater Occipital Nerve, Head, Orthodontics, Pain Threshold, Posture. Introduction Myofascial induction procedures form part of the commonly used spectrum of manual therapy manœuvres in clinical practice, and are targeted at myofascial areas compromised by restriction.1-3 However, its clinical efficacy has received only sparse attention in the scientific literature.4 For Quintana Aparicio et al., 5 some manœuvres not only have a local effect, but generate changes and responses at a distance. It has been found that these techniques reduce the subject's level of anxiety, affect certain physiological parameters including heart rate and blood pressure, 4 may increase local range of movement 6 and improve sleep quality and overall physical function.7 Within the myofascial procedures, the suboccipital muscle inhibition technique (SMI technique) is of great importance for the craniocervical region, and is often used to reduce the build-up of tension in the deep upper cervical tissues 1-3,5 Forward head posture (FHP) is one of the commonest unstructured postural disorders, being observed in two out of every three subjects.8 It is defined as a head which is held forward of the body's centre of gravity.9 For every inch the head moves forward, the additional force applied to the neck muscles is estimated to be from 15 to 30 pounds.10 This anomalous head position leads to a number of clinical conditions that may affect different bodily functions and systems.1,11 Among them, it is considered that the FHP leads to increased tone of different cervical muscles (scalene, trapezius, sternocleidomastoid..) and the four muscles controlling posture at the level of the neck. Three of them form the so-called suboccipital triangle: (i) rectus capitis posterior major, (ii) obliquus capitis inferior and (iii) obliquus capitis superior. The rectus capitis posterior minor is extremely associated with the suboccipital triangle. 1,12-13 On one hand, retraction of the suboccipital muscles can result in compression of the occipital nerves, and consequently may produce an increased sensitivity to any stimulus.1 On the other hand, it can also lead to a continuous triggering of nociceptive afferents in the caudate nucleus of the trigeminal nerve, causing central-type sensitization.14 In addition, FHP is considered to be a risk factor for temporomandibular dysfunction 15 and decreased neck mobility.16-17 Based on the results collected by Cureton 18, it is generally accepted that the use of lateral photographs is the simplest, cheapest, and most valid and reliable method of assessing craniocervical posture.19 It removes the subjectivity of grading the FHP as mild, moderate, or severe based on the clinical experience of each professional and on the individual perception of what is considered to be "normal".20 With respect to a nerve's mechanosensitivity, this can be evaluated using non-invasive mechanical stimuli that allow quantification of the pressure-pain threshold (PPT).21 Tecco et al. 22 found that the use of orthodontics increases high cervical lordosis and produces a tendency to mandibular prognathism, as is the case with FHP.1 In a study with a group of 55 mouth breathing girls who underwent maxillary expansion treatment, Tecco et al.23 observed increased extension in the high cervical region associated with overall flexion of the head, as is the case with FHP 1. Their findings, however, differ from those of Strini et al. 24 Even though they agree that orthodontic treatment modifies the balance of the masticatory muscles affecting the normal resting position of the head, they contend that this change is in the sense of normalizing head posture.24 We hypothesized that, in correcting tooth alignment, orthodontic treatment will affect the normal resting position of the jaw and the entire Cranio-Cervico-Mandibular Unit, favouring extension of the high cervical segment and the tendency to flexion of the lower cervical spine, so leading to a FHP, as suggested by Tecco et al 22-23. This correlates with a retraction of the suboccipital muscles and a decreased pressure pain threshold of the greater occipital (GO) nerve, a threshold which we shall find to be improved following application of the SMI technique. Thus, the objective of the study was to determine and analyze the differences in head posture and in the PPT of the GO nerve following an intervention by a SMI technique among asymptomatic subjects with a history of having used orthodontics. As suggested by Saíz LLamosas et al. 6 the study of the potential effects and benefits of myofascial induction techniques should be started in pain-free subjects to avoid any sensitization. Materials and Methods Design and Subjects The experimental protocol was a randomized, by means of sealed opaque envelopes, and single blind design (no communication between the therapist in charge of the intervention and the therapist who performed the measurements). Being the difference in craniocervical posture means (seated and standing) from pre to post intervention of 2º (SD 1.50 º), for an α value of .05 and a statistical power of 80%, a sample size of 12 subjects per group was necessary (software: tamaño de la muestra 1.1®). Students of the School of Nursing, Physiotherapy, and Podiatry of the University of Seville were selected by the main author based on non-probabilistic convenience sampling according to the following criteria: (i) age between 18-25 years old; (ii) a history of having used orthodontics for at least one year; (iii) absence of symptoms in the cervical spine, upper limbs and craniofacial area within the past four weeks previous to data collection; (iv) willingness to participate in the study as declared in signing the informed consent form. The exclusion criteria were: (i) having suffered a whiplash; (ii) a history of degenerative disorders of the central and/or peripheral nervous system; (iii) a history of cranial vault, craniofacial, temporomandibular joint, or any level of spinal fractures and/or surgery; (iv) suffering or having suffered osteitis, or cranial-vault, craniofacial, or temporomandibular joint rheumatic or tumoural diseases; (v) receiving soft tissue therapy within the year before the study and (vi) consumption of analgesics or anti-inflammatory drugs within 48 hours prior to data collection. The sample group consisted of 24 subjects (N = 24), 5 men and 19 women, mean age 21 ± 1.78 years (18--24 years). They were divided randomly into a Control Group (n = 12) and an Experimental Group (n = 12) by the therapist who performed the interventions. The process of intervention and data collection was conducted in the School of Physiotherapy and Podiatry at the University of Seville from June to September 2010 by two physiotherapists with more than 10 years of healthcare experience, maintaining similar ambient conditions on the successive days. The study received approval and was designed conformed to the guidelines of the Ethical Committee of Experimentation, University of Sevilla, and it has been registered in the ANZCTR (Australian New Zealand Clinical Trials Registry) with registration number ACTRN12611001028998. Evaluation of the craniovertebral angle The craniovertebral angle (CVA) is measured to be that between a horizontal line that crosses the body of the seventh cervical vertebra (C7) and the line from the tragus of the ear to the spinal apophysis of C7. Two lateral photographs are taken of the subject seated and standing still, following the methodological indications described in recent studies 14, 16, 25. For the first photograph, the subjects were asked to sit with their arms on their legs, and to rest their back and buttocks on the back of the chair, with both feet on the ground. The examiner instructed them to fix their gaze on an imaginary point on the wall directly in front. For the second photograph, the subjects stood still in a posture as natural as possible, with arms resting along the body, and directing their gaze as in the previous case. Photographs were made from the subject's right with a Nikon Coolpix E-5600 digital camera. Evaluation of the greater occipital nerve pain-pressure threshold Measurements were made with a Model FPX 25 digital algometer (Wagner Instruments Greenwich, CT), using a 1cm² area contact head, and applying a perpendicular pressure gradient of approximately 1kg/cm²/s. For the palpation of the GO nerve, we followed the indications described by Loukas et al.26 and Mosser et al., 27 locating it laterally with a finger, and approximately one finger's length caudally from the external occipital crest. The reference points on both sides of the head were labelled with a marker, and three measurements were made at each one with a resting period of 30 seconds between each measurement (figure 1). All the subjects were instructed identically: "Let me know when the sensation of pressure becomes uncomfortable or painful". The reference value was taken as the mean of the three measurements. ### FIGURE 1 ### Intervention procedure for the Experimental Group The SMI technique was performed according to the literature. 1,3,5,28 With the patient supine, the therapist sits at the head of the table and places the palms of her hands under the subject's head, her fingers contacting the occipital condyles. Then, the therapist locates with the middle and ring fingers of both hands the space between the occipital condyles and the spinal process of the second cervical vertebra. Then, with the metacarpophalangeal joints in 90° flexion, she rests the base of the skull on her hands and exerts a constant, but not painful, pressure ventrally, maintaining the index, middle, and ring fingers of both hands extended and together. A very slight traction can be added cranially to decongest the suboccipital zone (figure 2). Once the tissue relaxation has been attained, contact is smoothly released, leaving the subject's head resting on the table. During the SMI technique, the subject is asked to keep his eyes closed to avoid eye movements affecting the suboccipital muscle tone.1 It was set an intervention time of four size. Conflict of Interests and Funding Sources The authors declare no conflict of interests or funding sources for this study. References 1. Pilat, A. 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Weibelt S, Andress-Rothrock D, King W, Rothrock J. Suboccipital Nerve Blocks for Suppression of Chronic Migraine: Safety, Efficacy, and Predictors of Outcome. Headache 2010; 50:1041-44 42. Sun-Edelstein C, Mauskop A. Alternative Headache Treatments: Nutraceuticals, Behavioral and Physical Treatments. Headache 2011; 51:469-83 Figures and Tables Fig 1. Evaluation of Greater Occipital nerve pressure-pain threshold Black circle (External Occipital Crest) White circle (Greater occipital nerve) Fig 2. Suboccipital Muscle Inhibition technique (Experimental Group) Fig 3. Placebo technique (Control Group) Fig 4. Box-and-whisker plot of the seated and standing Craniovertebral Angle in the studied groups Table 1. Physical and clinical characteristics of the studied sample Table 2. Differences in the means between-groups of the changes from post- to preintervention of the Craniovertebral Angle, and the pain-pressure threshold (PPT) of the Greater Occipital nerve (GON) Table 1. Physical and clinical characteristics of the studied sample Control Group Experimental Group Difference Age (yrs) 21 ± 1.59 21 ± 1.83 Distribution by sex (man ♂, woman ♀) 3 ♂ ; 9 ♀ 2 ♂; 11 ♀ Height (cm) 168.58 ± 6.44 166.58 ± 4.66 p = 0.393* Weight (kgs) 63.5 ± 10.68 65.91 ± 8.77 p = 0.551* Handedness (right; left; ambidextrous) (%) 91.7%; 8.3%; 0%) 91.7%; 8.3%; 0% p = 1.000* Years of use of orthodontia 2.91 ± 0.51 2.50 ± 0.52 p = 0.066* Type of orthodontia (fixed; removable) (%) 91.7%; 8.3% 91.7%; 8.3% p = 1.000* Presence of material retention (yes; no) (%) 66.7%; 33.3% 75%; 25% p = 0.660* Seated Craniovertebral Angle (°) 58.16 ± 4.38 56.33 ± 4.33 p = 0.314* Standing Craniovertebral Angle (°) 50.75 ± 6.22 49.66 ± 4.07 p = 0. 619* PPT (kg/cm²) GON Dominant Side 1.80 ± 0.47 2.12 ± 0.99 p = 0.335* PPT (kg/cm²) GON Non-Dominant Side 1.90 ± 0.46 2.11 ± 0.86 p = 0.456* One-year Prevalence of Headache or Migraine (%) 58.33% (7/12) 50 % (6/12) p = 0.688* One-year Prevalence of Cervical or Mandibular pain (%) 8.33% (1/12) 25% (3/12) p = 0.284* Data are reported as mean ± SD or in percentages (%); GON, Greater Occipital Nerve Difference: statistical significance of the between-group difference. * Not statistically significant (P > 0.05) Table 2. Differences in the means between-groups of the changes from post- to preintervention of the Craniovertebral Angle, and the pain-pressure threshold (PPT) of the greater occipital nerve (GON) Data are reported as mean ± SD (95% confidence intervals) * Indicates statistically significant difference between groups (p<0.05) Control Experimental CranioVertebral Angle Seated * (Post-Pre Intervention) -0.25° ± 0.86° 5.91° ± 1.92° (-7.43 , - 4.90) CranioVertebral Angle Seated * (Post-Pre Intervention) 0.75° ± 0.86° 3.25° ± 1.65° (-3.64 , - 1.35) PPT ( kg/cm2) GON Dominant Side (Post-Pre Intervention) - 0.03 ± 0.34 0.13 ± 0.28 (-0.43 , 0.09) PPT( kg/cm2) GON Non-Dominant Side * (Post-Pre Intervention) - 0.14 ± 0.26 0.18 ± 0.34 (-0.59 , - 0.07) Fig 1. Evaluation of GO nerve PPT, black circle (external occipital crest) and white circle (GO nerve).