Journal of Clinical Medicine Article Interaction between Pain, Disability, Mechanosensitivity and Cranio-Cervical Angle in Subjects with Cervicogenic Headache: A Cross-Sectional Study Patricia Martínez-Merinero 1, Fernando Aneiros Tarancón 2, Javier Montañez-Aguilera 3 , Susana Nuñez-Nagy 4, Daniel Pecos-Martín 4,5 , Rubén Fernández-Matías 5 , Alexander Achalandabaso-Ochoa 5,6,* , Samuel Fernández-Carnero 4,5 and Tomás Gallego-Izquierdo 4,5 1 Physiotherapy Department, Faculty of Health, Exercise and Sport, European University, Villaviciosa de Odón, 28660 Madrid, Spain; [email protected] 2 Physiotherapy Center, Alcalá University, 28871 Alcalá de Henares, Spain; [email protected] 3 Department of Physiotherapy, Universidad Cardenal Herrera-CEU, 46115 Alfara del Patriarca, Spain; [email protected] 4 Department of Physiotherapy and Nursing, Alcalá University, 28871 Alcalá de Henares, Spain; [email protected] (S.N.-N.); [email protected] (D.P.-M.); [email protected] (S.F.-C.); [email protected] (T.G.-I.) 5 Research Institute of Physical Therapy and Pain, Alcalá University, 28871 Alcalá de Henares, Spain; [email protected] 6 Department of Health Sciences, Universidad de Jaén, 23071 Jaén, Spain * Correspondence: [email protected] Citation: Martínez-Merinero, P.; Aneiros Tarancón, F.; Abstract: The relationship between the forward head posture and mechanosensitivity in subjects Montañez-Aguilera, J.; Nuñez-Nagy, with a cervicogenic headache (CGH) remains uncertain. The aim of the study was to evaluate if S.; Pecos-Martín, D.; there was a relationship between the tissue mechanosensitivity and cranio-cervical angle (CCA) that Fernández-Matías, R.; Achalandabaso-Ochoa, A.; was moderated by pain intensity and/or disability in subjects with CGH. A convenience sample of Fernández-Carnero, S.; 102 subjects was recruited. The CCA was measured with photographs, using a postural assessment Gallego-Izquierdo, T. Interaction software. The pain intensity was measured with a visual analogue scale (VAS), and the disability was between Pain, Disability, measured with the Northwick Park Questionnaire. The pressure pain threshold (PPT) was measured Mechanosensitivity and at the spinous process of C2, the upper trapezius and splenius capitis muscles, and the median nerve. Cranio-Cervical Angle in Subjects Simple moderation multiple regression analyses were constructed. There was a positive relationship with Cervicogenic Headache: between PPT at C2 and CCA, but a nonsignificant relationship for the PPT measured at the muscles A Cross-Sectional Study. J. Clin. Med. and median nerve. The effect of PPT at C2 over CCA was moderated by pain intensity (R2 = 0.17; 2021, 10, 159. https://doi.org/ R2 change = 0.06; p < 0.05) but not disability. The Johnson–Neyman analysis revealed a cut-off point 10.3390/jcm10010159 for the statistical significance of 4.66 cm in VAS. There seems to be a positive relationship between PPT at C2 and CCA, which is positively moderated by pain intensity in subjects with CGH. Received: 25 November 2020 Accepted: 2 January 2021 Published: 5 January 2021 Keywords: forward head posture; mechanosensitivity; pressure pain threshold; cervicogenic headache Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- 1. Introduction nal affiliations. The term cervicogenic headache (CGH) refers to a headache caused by a dysfunction in the cervical spine and its osseous, disc and/or soft tissue components, which is usually accompanied by cervical pain [1] and one-sided pain referred to the head [2]. Cervical pain has been proposed as a possible trigger for headache [3] because of the convergence in the Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. trigeminal nucleus caudalis [4]. Cervical pain is one of the most common musculoskeletal This article is an open access article complaints in the adult population, with an annual incidence ranging from 10.4% to 21.3% distributed under the terms and con- and a prevalence of up to 86.8% in developed countries [5]. On the other side, headaches ditions of the Creative Commons At- have an estimated prevalence of up to 4.6%, with CGH representing 17% of all headache tribution (CC BY) license (https:// types [6] and generating an annual cost of 173 billion euros in European Union countries [7]. creativecommons.org/licenses/by/ The high prevalence and elevated associated costs explain why the research in this field 4.0/). has increased in the last years [8,9]. J. Clin. Med. 2021, 10, 159. https://doi.org/10.3390/jcm10010159 https://www.mdpi.com/journal/jcm J. Clin. Med. 2021, 10, 159 2 of 10 It has been suggested that cranio-cervical pain is related to posture alterations [10], forward head posture (FHP) being one of the most investigated, which is characterized by a decreased cranio-cervical angle (CCA) [11] leading to an extension of the occipital and upper cervical spine and a flexion of the medium-lower cervical spine [3]. This pos- ture induces a lengthening of the cervical extensors and occipital flexors muscles, and a shortening of the cervical flexor muscles and suboccipital muscles [12], which are the most shortened [13]. It has been suggested that FHP could impose a great mechanical demand in differ- ent tissues in the cranio-cervical region, sensitizing them and thus contributing to the appearance and/or perpetuation of pain [14]. Multiple authors have investigated the relationship between tissue mechanosensitivity, posture alterations and neck pain [15–18], with some finding an increase of mechanosensitivity in subjects with FHP [17,18]. Fur- thermore, Castien et al. [16] have found an association between headache intensity and mechanosensitivity for some tissues of the cranio-cervical region [16]. Despite emerging research about the relationship between FHP, tissue mechanosen- sitivity and cervical pain, it is not known if this relationship exists in subjects with CGH. The aim of the present study is to evaluate if there is a relationship between tissue mechanosensitivity and CCA that is moderated by the pain intensity and/or the degree of disability in subjects with CGH. 2. Materials and Methods 2.1. Design A cross-sectional study was conducted following the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) recommendations [19] and according to the Declaration of Helsinki. Ethical approval was obtained from Universidad CEU Cardenal Herrera (CEI16/011). 2.2. Subjects A convenience sample of subjects with CGH was recruited through announcements in the city of Alcalá de Henares. All subjects signed an informed consent form before participation in the study. Demographic data about the weight, height, age, sex and body mass index (BMI) were collected from all subjects. All subjects met the criteria described in the third edition of the International Classification of Headache Disorders for CGH [1]. The inclusion criteria were: older than 18 years, suffered from cervical pain with associated unilateral headaches from at least three months, and had less than 32 degrees of cervical rotation in the cervical flexion-rotation test evaluated with a cervical goniome- ter [20]. Subjects were excluded if they presented: systemic diseases, previous cervical surgery, trauma in the last six months, diagnosis of migraine or another possible cause of headaches, and/or neurological symptoms. 2.3. Sample Size The sample size was calculated based on the increase of the determination coefficient (R2) with the addition of the interaction term in a hierarchical multiple regression analysis. Assuming that only one predictor (interaction term) was tested with the R2 change, nine predictors were included in the model in the first step, there was an effect size of 0.10, 80% power and a value of 0.05, 81 subjects had to be recruited. Assuming a 20% rate of dropouts, the final sample size was composed of 102 subjects. 2.4. Measurements All variables were measured at the University of Alcalá, Physiotherapy and Pain Research Center (Madrid, Spain) by two physiotherapists with more than 10 years of experience in manual therapy who were blinded to each other’s measurements. One phys- iotherapist evaluated the tissue’s mechanosensitivity, and the other one evaluated the CCA. J. Clin. Med. 2021, 10, 159 3 of 10 2.4.1. Pain Intensity and Disability A visual analogue scale (VAS) was used for the measurement of the pain intensity during the last week; the VAS is a reliable tool (r = 0.94) ranging from 0 (no pain) to 10 (worst imaginable pain) [21]. Disability was measured with the Northwick Park Questionnaire (NPQ), a valid tool with an intraclass correlation coefficient (ICC) value of 0.63, which was transculturally adapted into Spanish (Spain) in 2001 [22]. The NPQ ranges from 0 (no disability) to 100 (maximum degree of disability). 2.4.2. Cranio-Cervical Angle For the measurement of the CCA, a reflex camera (Nikon Model D5300 SLR, Tokyo Japan) was used to take photographs that were analyzed with a postural assessment software [23,24]. The camera was fixed three meters away from the standing subject, who was told to maintain a relaxed posture. One photograph per subject was taken [23,24]. Two lines were traced using as a reference two markers placed on the tragus of the ear and the spinous apophysis of the 7th cervical vertebrae (C7). The first line was a horizontal line crossing the C7 marker, and the second line was an oblique line linking the C7 and tragus markers. The CCA corresponded to the angle between the two lines. The measurement of the CCA, as stated above, has shown good reliability with an ICC value of 0.98 and good validity in comparison to radiography (r = 0.89) [25]. 2.4.3. Pressure Pain Threshold The pressure pain threshold (PPT), measured with a hand-held algometer (Wagner Force Dial, Model FDK 20, Wargner Instruments, Greenwich, CT, USA), was used as an esti- mator of tissues’ mechanosensitivity.