Immediate and Short-Term Effects of Upper Cervical High-Velocity, Low-Amplitude Manipulation on Standing Postural Control and Cervical Mobility in Chronic Nonspecific Neck Pain: A Randomized Controlled Trial

Journal of Clinical Medicine Article Immediate and Short-Term Effects of Upper Cervical High-Velocity, Low-Amplitude Manipulation on Standing Postural Control and Cervical Mobility in Chronic Nonspecific Neck Pain: A Randomized Controlled Trial Francisco Gómez 1, Pablo Escribá2, Jesús Oliva-Pascual-Vaca 3,4 , Roberto Méndez-Sánchez 5,* and Ana Silvia Puente-González 5 1Centro Fisioterapia y Osteopatía Osteofisio, 12006 Castellón, Spain; [email protected] 2Clínica Fisioterapia y Osteopatia Pablo Escribá, Alboraya, 46120 Valencia, Spain; [email protected] 3Department of Physiotherapy, Universidad de Sevilla, 41009 Sevilla, Spain; [email protected] 4Department of Physiotherapy, University School of Osuna, Universidad de Sevilla, Osuna, 41640 Sevilla, Spain 5Department of Nursing and Physiotherapy, Universidad de Salamanca, 37007 Salamanca, Spain; [email protected] *Correspondence: [email protected]; Tel.: +34-923-294-590 Received: 1 May 2020; Accepted: 7 August 2020; Published: 10 August 2020   Abstract: This study aimed to determine the immediate and short-term effects of a single upper cervical high-velocity, low-amplitude (HVLA) manipulation on standing postural control and cervical mobility in chronic nonspecific neck pain (CNSNP). A double-blinded, randomized placebo-controlled trial was performed. Forty-four patients with CNSNP were allocated to the experimental group (n=22) or control group (n=22). All participants were assessed before and immediately after the intervention, with a follow-up on the 7th and 15th days. In each evaluation, we assessed global and specific stabilometric parameters to analyze standing postural balance and performed the cervical flexion-rotation test (CFRT) to analyze upper cervical mobility. We obtained statistically significant differences, with a large effect size, in the limited cervical rotation and global stabilometric parameters. Upper cervical HVLA manipulation produced an improvement in the global stabilometric parameters, significantly decreasing the mean values of velocity, surface, path length, and pressure in all assessments (p<0.001; η2p=0.323–0.856), as well as significantly decreasing the surface length ratio (L/S) on the 7th ( − 0.219 1/mm; p=0.008; 95% confidence interval (CI): 0.042–0.395) and 15th days ( − 0.447 1/mm; p<0.001; 95% CI: 0.265–0.629). Limited cervical rotation values increased significantly immediately after manipulation (7.409 ◦ ;p<0.001; 95% CI: 6.131–8.687) and were maintained during follow-up (p<0.001). These results show that a single upper cervical HVLA manipulation produces an improvement in standing postural control and increases the rotational range of motion (ROM) in the upper cervical spine in patients with CNSNP. Keywords: upper cervical spine; chronic neck pain; musculoskeletal disorders; HVLA manipulation; cervical range of motion; postural balance 1. Introduction Neck pain can be defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage in the neck region” [ 1 ]. It is a common problem that an estimated 67% of the population will suffer from at some moment in their life [ 2 ]. The most frequent form of J. Clin. Med. 2020,9, 2580; doi:10.3390/jcm9082580 www.mdpi.com/journal/jcm J. Clin. Med. 2020,9, 2580 2 of 18 clinical presentation is nonspecific or mechanical neck pain [ 3 ]. Some of these patients, after the first episode of cervical pain, will experience a new episode in the following years, most of them in the first year [ 3 ], and some of them will not experience complete resolution of pain and disability, which can become a more complex chronic pain syndrome [4]. Chronic nonspecific neck pain (CNSNP) is a neck pain not due to organic pathology or that it has an unknown pathological basis as the underlying cause over the last 12 weeks or more, and is associated with a high economic cost for health [ 3 – 5 ], becoming a socio-health problem, since it is associated with disability, muscular alterations, decreased cervical range of motion (CROM) and greater sensitivity to pain [ 3 ]. It also relates to alterations of kinesthesia and the proprioceptive system, like postural stability disturbance and joint position sense deficit [ 6 – 8 ], according to a systematic review where nonspecific neck pain and the whiplash associated disorder exhibit postural instability with greater center of pressure (COP) excursions [ 9 ]. It has also been proven that experimental neck muscle pain significantly impairs standing balance, suggesting the need for intact neck neuromuscular function for the maintenance of a standing posture [10]. Proprioception is the interoceptive sense that includes kinesthesia (movement sense) and the position sense (joint position sense) [ 11 , 12 ]. It is also essential for effectual sensorimotor control, with important roles in feed-back and feed-forward control [ 13 ]. The cervical sensory afferents are involved in balance control and have relatively strong influences on the vestibular and visual system [ 13 , 14 ]. It is also known that muscle spindles are major kinesthetic proprioceptors, with a very high density, specifically in the suboccipital region [15]. Some studies have shown evidence of the benefit of manual therapy, observing that is possible to enhance kinesthetic sensitivity and proprioception [ 16 ]. Different effects have been observed after high-velocity, low-amplitude (HVLA) manipulation in different regions, such as peripheral joints [ 17 , 18 ], sacroiliac joints [ 19 , 20 ], and the spine [ 21 , 22 ], both on pain and functionality [ 21 – 24 ], as well as neurophysiological effects on cortical somatosensory integration and function due to transient cortical plastic changes [ 25 ], on the neuromuscular system [ 23 , 25 , 26 ], kinesthesia [ 21 ], and global postural control [ 26 ]. The neurophysiological effects after HVLA manipulation seem to be proven, although, the clinical relevance, in relation to the neurophysiological changes, is not completely known [ 23 ]. For this, as the systematic review by Honor é et al. indicates, it would be important to review the previous studies considering the effect size, not only in regard to the immediate effects, but also the medium and long-term effects [ 27 ] because usual treatments for chronic neck pain achieve at most moderate effects in the short-term [28]. The last Clinical Practice Guideline by the American Physical Therapy Association recommended the use of cervical HVLA manipulation for the management of neck pain guided by impairment and function related assessment of the cervical spine [ 29 ]. In addition, some studies reported positive results on load distribution and postural control after HVLA manipulation in different regions [ 17 – 20 , 30 , 31 ], while other studies showed low or no clinical effects [32,33]. Patients with mechanical neck pain have C1-C2 rotational mobility restriction [ 34 ], and we know that cervical rotation affects standing postural control [ 35 ], considering that muscle spindles are major kinesthetic proprioceptors, with a very high density, specifically in the suboccipital region [15]. Thus, the purpose of this randomized clinical trial was to examine the acute and short-term effects of a single upper cervical spine (C1-C2) HVLA rotational thrust manipulation on CROM and standing postural control in patients with CNSNP. 2. Materials and Methods 2.1. Study Design A randomized, double blinded controlled trial, with two arms (experimental and control), was conducted to evaluate the acute and short-term effects of the intervention. The experimental group received a single upper cervical spine (C1-C2) HVLA rotational thrust manipulation, while the J. Clin. Med. 2020,9, 2580 3 of 18 control group received a sham technique. There were four assessments, at baseline, immediately after the intervention, and on the 7th and 15th days after the intervention. The study protocol complied with the ethical guidelines of research involving human subjects, was conducted according to the Helsinki Declaration, was previously approved by the Institutional Ethics Committee, and was prospectively registered in the Australian New Zealand Clinical Trials Registry, anzctr.org.au (ACTRN12615000214538). 2.2. Sample Size Calculation The sample size was based on a preliminary pilot study (12 subjects), using the free software “GRANMO simple size calculator” (7.12 version) and considering the surface length ratio (L/S) (1/mm), also called the length in function of surface (LFS), for the calculation, since it was the most demanding primary outcome in the calculation. L/S is the ratio of stroke length and the surface of the ellipse, and provides information about the accuracy of standing postural control and the energy cost or effort made by the subject. When L/S values decrease, subjects find maintaining the standing position harder, and the postural system requires more effort [ 36 ]. We determined that accepting an alpha risk of 0.05 and a beta risk of 0.2 in a bilateral contrast, a minimum of 22 subjects will be required in the first group and 22 in the second to recognize as statistically significant a difference equal or greater than 0.44 (1/mm). It was assumed that the common standard deviation is 0.4 and a drop-out rate of 10% was anticipated. 2.3. Participants and Recruitment In total, 44 patients were included in the study after selection criteria who voluntarily signed the informed consent (4 patients were excluded in the enrollment) (Figure 1). Patients were recruited consecutively in a private clinic (21 men and 23 women). They were between 18 and 60 years old, had CNSNP (over 12 weeks or more) higher than 2 in an 11-point Numeric Pain Rating Scale (NPRS) [ 37 ], with positive CFRT in one side (below 32–33 degrees) [ 38 , 39 ], and without any contraindication to cervical manipulation. Exclusion criteria were (a) vascular, neurological, or rheumatic pathology, or congenital malformations in the head or cervical spine; (b) alterations that affect the balance or postural control (e.g., dizziness, vertebrobasilar insufficiency, or Klein test positive); (c) traumatic antecedents on head or spine (e.g., fractures, sprains, whiplash); (e) pain in regions other than the neck or head during the assessments; (f) drug treatment (e.g., muscle relaxant, analgesic, anti-inflammatory). J. Clin. Med. 2020, 9, x FOR PEER REVIEW 3 of 17 the intervention, and on the 7th and 15th days after the intervention. The study protocol complied with the ethical guidelines of research involving human subjects, was conducted according to the Helsinki Declaration, was previously approved by the Institutional Ethics Committee, and was prospectively registered in the Australian New Zealand Clinical Trials Registry, anzctr.org.au (ACTRN12615000214538). 2.2. Sample Size Calculation The sample size was based on a preliminary pilot study (12 subjects), using the free software “GRANMO simple size calculator” (7.12 version) and considering the surface length ratio (L/S) (1/mm), also called the length in function of surface (LFS), for the calculation, since it was the most demanding primary outcome in the calculation. L/S is the ratio of stroke length and the surface of the ellipse, and provides information about the accuracy of standing postural control and the energy cost or effort made by the subject. When L/S values decrease, subjects find maintaining the standing position harder, and the postural system requires more effort [36]. We determined that accepting an alpha risk of 0.05 and a beta risk of 0.2 in a bilateral contrast, a minimum of 22 subjects will be required in the first group and 22 in the second to recognize as statistically significant a difference equal or greater than 0.44 (1/mm). It was assumed that the common standard deviation is 0.4 and a drop-out rate of 10% was anticipated. 2.3. Participants and Recruitment In total, 44 patients were included in the study after selection criteria who voluntarily signed the informed consent (4 patients were excluded in the enrollment) (Figure 1). Patients were recruited consecutively in a private clinic (21 men and 23 women). They were between 18 and 60 years old, had CNSNP (over 12 weeks or more) higher than 2 in an 11-point Numeric Pain Rating Scale (NPRS) [37], with positive CFRT in one side (below 32–33 degrees) [38,39], and without any contraindication to cervical manipulation. Exclusion criteria were a) vascular, neurological, or rheumatic pathology, or congenital malformations in the head or cervical spine; (b) alterations that affect the balance or postural control (e.g., dizziness, vertebrobasilar insufficiency, or Klein test positive); (c) traumatic antecedents on head or spine (e.g., fractures, sprains, whiplash); (e) pain in regions other than the neck or head during the assessments; (f) drug treatment (e.g., muscle relaxant, analgesic, antiinflammatory). Figure 1. CONSORT flow diagram. Figure 1. CONSORT flow diagram. J. Clin. Med. 2020,9, 2580 4 of 18 2.4. Masking and Allocation We performed a double-blinded study, where the patients and the assessor were blinded. The patients did not know which were the interventions that were being compared. Further, the patients in the control group did not know that the ultrasound was turned off. In regard to the assessor, he did not know anything about the intervention that every patient had received. Thus, he did not know which group they belonged to. After the baseline assessment, the physiotherapist that applied the intervention performed the allocation. The randomization was undertaken using a computerized randomization system (randomized.com), and allocation concealment was guaranteed by sequentially numbered, opaque, sealed envelopes. An outside coworker safeguarded the sequence for those participating in the study. 2.5. Outcome Measures We considered CFRT and L/S as primary outcomes, which were used as inclusion criteria in the recruitment and selection of subjects and for the calculation of the sample size, respectively. 2.5.1. Cervical Flexion-Rotation Test (CFRT) The CFRT is a commonly and easily applied assessment to determine the presence of a joint dysfunction at the C1-C2 level, and has been reported to be a reliable and valid measurement of upper cervical movement [ 40 , 41 ]. It has shown excellent inter-tester reliability (ICC 0.93 (confidence interval (CI), 0.87–0.96)) and examiner agreement of its interpretation ( κ value 0.85). The validity to identify C1-C2 dysfunction also excellent (sensitivity 90%; specificity 88%) with a likelihood of a correct diagnosis of 89% [ 40 ]. Subjects lay down in supine position with the CROM ® instrument on the head (Platismo Airguide Inc Compas, Buffalo Groove, IL, USA) [ 39 , 40 ]. The evaluator performed a maximum range of cervical flexion in an attempt to block, as much as possible, above and below C1-C2. Then, the evaluator rotated the head to each side like Hall et al. described [ 38 , 40 , 42 ]. The mean of three measurements of each side was used for further analysis. The test is positive when there is a limitation of movement below 32–33 ◦ (10 ◦ less than the movement considered normal) [ 38 – 43 ]. The limitation is determined when resistance or pain appears in the cranio-cervical region when performing head rotation [43]. 2.5.2. Static Postural Stability Assessment Postural assessment was examined with the subjects standing on a force platform (NAMROL PODOPRINT, Software analysis PODOPRINT 2.9V, Medicapteurs, France, SAS) with the recommendations of the systematic review published by Ruhe A. et al. to achieve acceptable reliability for most COP parameters [ 44 ]. Data were sampled at 100 Hz, over 90 s, in the standing position, and different parameters of COP excursions were analyzed (displacements, velocities, areas and pressures) [ 44 – 46 ]. A positioner for the feet was used considering, as reference, the tubercle of the scaphoid, leaving a separation of 5 cm between the feet. Eyes were closed and the jaw was relaxed without occlusal contact. Before starting the measurement, the subjects were instructed to “be as still as possible with eyes closed, breathe normally, do not talk, do not tighten the jaw, and hold that position until I tell you” [18,20,44]. 2.6. Interventions The therapist that applied the interventions in both groups was an experienced physiotherapist and osteopath with more than 13 years experience treating patients suffering from neck pain by means of manipulative technics. After baseline assessment and performing the allocation, the subjects in both groups were treated with a different intervention for only one session. J. Clin. Med. 2020,9, 2580 5 of 18 2.6.1. Experimental Group A single upper cervical spine (C1-C2) HVLA rotational thrust manipulation was applied with the patient in the supine position. The rotational thrust was applied to the side that was positive in the CFRT. For a restricted left rotation, the physiotherapist was in contact with the right posterior arch of the atlas with the proximal index phalanx of the right hand and the left hand cradled the head of the patient. To localize the tension to the C1-C2 level secondary (posterior-anterior shift on the right posterior arch of the atlas and left side-shift) and primary (left rotation and right side-bend), levers of movements were used. Then, the physiotherapist applied a thrust in left rotation in an arc toward the underside eye and translation toward the table [ 24 , 34 , 47 ] (Figure 2). The patient remained on the table until an alarm went off, indicating when the technique had finished. J. Clin. Med. 2020, 9, x FOR PEER REVIEW 5 of 17 A single upper cervical spine (C1-C2) HVLA rotational thrust manipulation was applied with the patient in the supine position. The rotational thrust was applied to the side that was positive in the CFRT. For a restricted left rotation, the physiotherapist was in contact with the right posterior arch of the atlas with the proximal index phalanx of the right hand and the left hand cradled the head of the patient. To localize the tension to the C1-C2 level secondary (posterior-anterior shift on the right posterior arch of the atlas and left side-shift) and primary (left rotation and right side-bend), levers of movements were used. Then, the physiotherapist applied a thrust in left rotation in an arc toward the underside eye and translation toward the table [24,34,47] (Figure 2). The patient remained on the table until an alarm went off, indicating when the technique had finished. Figure 2. Upper cervical spine (C1-C2) high-velocity, low-amplitude (HVLA) rotational thrust manipulation for a restricted left rotation with positive cervical flexion-rotation test (CFRT). 2.6.2. Control Group The sham technique consisted of the physiotherapist placing his hands on the patient’s neck, without adding pressure or therapeutic intention, while a turned-off ultrasound was performed without movement of the head, simulating static application of the ultrasound, applied for one minute. At the end of the minute, an alarm went off, indicating that the time had finished. 2.7. Statistical Analysis Statistical analysis using IBM SPSS Statistics (v.23) and R Statistical Package (v.3.0.1) was performed (http://cran.r-project.org). Descriptive analysis of demographic and clinical characteristics was performed to summarize the data, including frequency for categorical variables and measures of central tendency and dispersion for continuous variables. Baseline data were compared between the manipulation group and control group using independent t tests for continuous variables, as well as chi square tests of independence for categorical variables. Figure 2. Upper cervical spine (C1-C2) high-velocity, low-amplitude (HVLA) rotational thrust manipulation for a restricted left rotation with positive cervical flexion-rotation test (CFRT). 2.6.2. Control Group The sham technique consisted of the physiotherapist placing his hands on the patient’s neck, without adding pressure or therapeutic intention, while a turned-offultrasound was performed without movement of the head, simulating static application of the ultrasound, applied for one minute. At the end of the minute, an alarm went off, indicating that the time had finished. 2.7. Statistical Analysis Statistical analysis using IBM SPSS Statistics (v.23) and R Statistical Package (v.3.0.1) was performed (http://cran.r-project.org). Descriptive analysis of demographic and clinical characteristics was performed to summarize the data, including frequency for categorical variables and measures of central tendency and dispersion for continuous variables. Baseline data were compared between the manipulation group and control group using independent t tests for continuous variables, as well as chi square tests of independence for categorical variables. J. Clin. Med. 2020,9, 2580 6 of 18 Two-way repeated measures ANOVA was performed (group * time). Group factor was considered as a categorical variable in the statistical model and time factor was used by taking into account the baseline and the three post-intervention data (immediate, 7th, and 15th days). The interaction between the two factors on the dependent variables was analyzed. Regardless of whether there is an interaction, follow-up tests (post-hoc) were performed to determine how the within-subjects factors affected the dependent variables. If a baseline value was found to be significantly different considering the baseline values, it was used as a covariate in the model. The post hoc Sidak test to determine which pairs of means have significant differences was calculated. Analysis of whether the values of two or more quantitative variables changed in conjunction was performed by correlations with Pearson’s r coefficient. The level of significance for the statistical tests was set at p ≤ 0.05 with the confidence interval of 95%. In order to assess the magnitude of the change in the result variables, the effect size of the upper cervical manipulation for the group * time ANOVA model was calculated as the partial eta squared ( η2p ) when significant, considering 0.01 small, 0.06 medium, and more than 0.14 a large effect size [ 48 ]. 3. Results 3.1. Descriptive Analysis Independent variables such us age, gender and anthropometric parameters (weight, height, and body mass index (BMI)), did not present significant differences between the experimental and the control group in baseline data. At that moment, we did not find significant differences before the intervention comparing the values of dependent variables between groups, except in the limited rotation, where, even finding differences between both groups, the values were within the data sought in the CFRT as positive (less than 32–33 ◦ ), so that both groups were considered homogeneous. Table 1 shows the characteristics of each group at the beginning of the study. Table 1. Descriptive baseline data of the experimental and control group. Means ± standard deviation are shown for continuous variables, and % (n) is shown for categorical variables. Variable Experimental Control p-Value Gender, women %(n) 50.00 (11) 54.55 (10) 0.763 Age (year) 38.36 ±11.664 37.50 ±11.827 0.809 Weight (Kg) 64.32 ±12.411 63.59 ±9.404 0.828 Height (m) 1.67 ±0.973 1.68 ±0.626 0.971 BMI (kg/m2)22.66 ±3.349 22.55 ±3.213 0.909 Limited Rotation (degrees) 31.36 ±0.902 30.14 ±1.167 <0.001 * Mean velocity (mm/s) 2.11 ±0.269 2.11 ±0.280 0.996 Surface length ratio L/S (1/mm) 1.63 ±0.455 1.67 ±0.289 0.721 Mean Surface (mm2)122.42 ±25.679 115.17 ±15.807 0.266 Mean Path length (mm) 189.20 ±24.147 189.50 ±25.256 0.998 Mean Pressure (g/cm2)313.28 ±51.123 299.65 ±65.406 0.445 Mean COP X −0.26 ±5.328 0.60 ±6.100 0.623 Mean COP Y −5.36 ±5.001 −3.67 ±1.912 0.145 Mean Anterior Velocity (mm/s) 1.24 ±0.366 1.16 ±0.201 0.390 Mean Lateral Velocity (mm/s) 0.76 ±0.181 0.85 ±0.171 0.131 * Indicates significant differences comparing between groups (t test for independent variables); BMI: Body mass index; COP: Center of pressure. 3.2. Inferential Analysis In the inferential analysis with two-way repeated measures ANOVA (Table 2), statistically significant differences were obtained for the group factor (regardless of time) with p<0.01 in the limited rotation, mean velocity, mean path length, and mean COP-Y, and with p=0.017 in L/S (Table 2). In the J. Clin. Med. 2020,9, 2580 7 of 18 interaction between factors (group * time), we observed significant differences, with p<0.01 in limited rotation and global stabilometric variables and with p<0.05 in some COP specific displacements variables (mean COP-Y, anterior, and lateral velocity). Table 2. Inferential statistics analysis for the group factor and the interaction between factors (time * group) with two-way repeated measures ANOVA. Effect size was calculated as the partial eta squared (η2p). Variable Group Time * Group Fp-Value (η2p) F p-Value (η2p) Limited Rotation (degrees) 132.087 * <0.001 0.759 46.447 * <0.001 0.777 Surface length ratio L/S (1/mm) 6.133 * 0.017 0.127 16.434 * <0.001 0.552 Mean velocity (mm/s) 41.636 * <0.001 0.498 78.990 * <0.001 0.856 Mean Surface (mm2)4.040 0.051 0.088 14.695 * <0.001 0.524 Mean Path length (mm) 41.668 * <0.001 0.498 78.180 * <0.001 0.854 Mean Pressure (g/cm2)<0.001 0.999 <0.001 6.374 * 0.001 0.323 Mean COP X 0.559 0.459 0.013 0.668 0.576 0.048 Mean COP Y 16.046 * <0.001 0.276 3.746 * 0.018 0.219 Mean Anterior Velocity (mm/s) 0.361 0.551 0.009 3.831 * 0.017 0.223 Mean Lateral Velocity (mm/s) 3.662 0.062 0.080 3.831 * 0.017 0.223 * Indicates significant differences; COP: Center of pressure. The effect size achieved with the intervention in the experimental group over time, compared with the control group, showed a large effect, especially in the limited cervical rotation and in the global stabilometric variables of COP displacement, being η2p>0.5 in all of them (Table 2). To analyze in more detail, the significant interaction between factors (group * time), we applied the post hoc Sidak test to determine which pairs of means have significant differences. We analyzed the comparisons between subjects from different groups in each evaluation and we also analyzed intragroup comparisons for the time factor (baseline, immediately after intervention, and 7th and 15th days). 3.2.1. Inter-Group Comparisons Limited cervical rotation showed significant differences between groups in all evaluations (p<0.01) (baseline differences already considered) (Figure 3), with a much higher mean value (between 6.8 and 8.3 degrees) with respect to the control group in three post-intervention evaluations (Table 3). In global stabilometric variables, similar values could be observed in all of them (Figure 4), except for the mean pressure, where no significant differences were obtained between groups in any of the evaluations, although a different intra-subject behavior was observed in both groups. In mean velocity, mean surface, and mean path length, the differences between groups began in the post-immediate evaluation and remained until the end of the study (p<0.01), while, in the L/S ratio, the differences were observed from the evaluation on the 7th day (p<0.01). In COP-specific displacements variables, we only observed significant differences between groups in mean COP-Y, from the post-immediate evaluation (p<0.01) (Table 3). J. Clin. Med. 2020,9, 2580 8 of 18 J. Clin. Med. 2020, 9, x FOR PEER REVIEW 8 of 17 Figure 3. Differences with 95% confidence interval in behavior during intra-subject follow-up of limited cervical rotation between both groups. Pre: Pre-intervention baseline data; Post: Postimmediate data; 7D: Data on the 7th day; 15D: Data on the 15th day. Table 3. Interaction between factors (time * group) showing the differences by group at each evaluation (post hoc Sidak test). Variable Time-Evaluation Differences (EG-CG) p-Value CI 95% Mean ±SEM Lower Upper Limited Rotation Baseline 1.227 * 0.314 <0.001 0.593 1.862 (degrees) Post-immediate 8.318 * 0.752 <0.001 6.800 9.836 7 days 7.909 * 0.667 <0.001 6.563 9.255 15 days 6.818 * 0.638 <0.001 5.530 8.106 Surface length ratio L/S Baseline −0.041 0.115 0.721 −0.273 0.190 (1/mm) Post-immediate −0.045 0.107 0.675 −0.262 0.171 7 days −0.235 * 0.073 0.002 −0.382 −0.089 15 days −0.460 * 0.065 <0.001 −0.591 −0.330 Mean velocity Baseline <0.001 0.083 0.996 −0.167 0.166 (mm/s) Post-immediate −0.271 * 0.077 0.001 −0.427 −0.116 7 days −0.645 * 0.072 <0.001 −0.791 −0.498 15 days −0.867 * 0.076 <0.001 −1.021 −0.713 Mean Surface Baseline 7.246 6.429 0.266 −5.728 20.220 (mm2) Post-immediate −8.786 6.427 0.179 −21.757 4.184 7 days −20.845 * 5.535 0.001 −32.016 −9.675 15 days −21.023 * 5.276 <0.001 −31.670 −10.376 Mean Path length Baseline 0.018 7.450 0.998 −15.016 15.052 (mm) Post-immediate −24.564 * 6.923 0.001 −38.536 −10.592 7 days −57.945 * 6.517 <0.001 −71.098 −44.793 15 days −78.023 * 6.892 <0.001 −91.932 −64.113 Mean Pressure Baseline 13.638 17.699 0.445 −22.080 49.356 (g/cm2) Post-immediate −1.836 16.789 0.913 −35.717 32.045 7 days −5.280 16.415 0.749 −38.406 27.846 15 days −6.623 16.735 0.694 −40.394 27.149 Mean COP X Baseline −0.855 1.727 0.623 −4.339 2.630 Figure 3. Differences with 95% confidence interval in behavior during intra-subject follow-up of limited cervical rotation between both groups. Pre: Pre-intervention baseline data; Post: Post-immediate data; 7D: Data on the 7th day; 15D: Data on the 15th day. J. Clin. Med. 2020, 9, x FOR PEER REVIEW 9 of 17 Post-immediate −1.600 1.704 0.353 −5.039 1.839 7 days −1.255 1.578 0.431 −4.439 1.930 15 days −1.091 1.557 0.487 −4.232 2.051 Mean COP Y Baseline −1.695 1.143 0.145 −4.001 0.610 Post-immediate −3.477 * 0.958 0.001 −5.410 −1.545 7 days −4.259 * 0.874 <0.001 −6.022 −2.496 15 days −4.486 * 0.913 <0.001 −6.330 −2.643 Mean Anterior Velocity Baseline 0.077 0.089 0.390 −0.102 0.257 (mm/s) Post-immediate −0.045 0.073 0.535 −0.192 0.101 7 days −0.118 0.068 0.088 −0.255 0.018 15 days −0.077 0.080 0.342 −0.240 0.085 Mean Lateral Velocity Baseline −0.082 0.053 0.131 −0.189 0.025 (mm/s) Post-immediate −0.145 0.076 0.062 −0.299 0.008 7 days −0.136 0.083 0.106 −0.303 0.030 15 days −0.155 0.078 0.053 −0.311 0.002 * Indicates significant differences; EG: Experimental Group; CG: Control Group; CI: Confidence interval; SEM: Standard error of the mean; COP: Center of pressure. Figure 4. Differences with 95% confidence interval in behavior during intra-subject follow-up of global stabilometric variables between both groups. L/S: Length in function of the surface; Pre: Preintervention baseline data; Post: Post-immediate data; 7D: Data on the 7th day; 15D: Data on the 15th day. 3.2.2. Intra-Group Comparisons Figure 4. Differences with 95% confidence interval in behavior during intra-subject follow-up of global stabilometric variables between both groups. L/S: Length in function of the surface; Pre: Pre-intervention baseline data; Post: Post-immediate data; 7D: Data on the 7th day; 15D: Data on the 15th day. J. Clin. Med. 2020,9, 2580 9 of 18 Table 3. Interaction between factors (time * group) showing the differences by group at each evaluation (post hoc Sidak test). Variable Time-Evaluation Differences (EG-CG) p-Value CI 95% Mean ±SEM Lower Upper Limited Rotation Baseline 1.227 * 0.314 <0.001 0.593 1.862 (degrees) Post-immediate 8.318 * 0.752 <0.001 6.800 9.836 7 days 7.909 * 0.667 <0.001 6.563 9.255 15 days 6.818 * 0.638 <0.001 5.530 8.106 Surface length ratio L/S Baseline −0.041 0.115 0.721 −0.273 0.190 (1/mm) Post-immediate −0.045 0.107 0.675 −0.262 0.171 7 days −0.235 * 0.073 0.002 −0.382 −0.089 15 days −0.460 * 0.065 <0.001 −0.591 −0.330 Mean velocity Baseline <0.001 0.083 0.996 −0.167 0.166 (mm/s) Post-immediate −0.271 * 0.077 0.001 −0.427 −0.116 7 days −0.645 * 0.072 <0.001 −0.791 −0.498 15 days −0.867 * 0.076 <0.001 −1.021 −0.713 Mean Surface Baseline 7.246 6.429 0.266 −5.728 20.220 (mm2) Post-immediate −8.786 6.427 0.179 − 21.757 4.184 7 days −20.845 * 5.535 0.001 − 32.016 −9.675 15 days −21.023 * 5.276 <0.001 − 31.670 − 10.376 Mean Path length Baseline 0.018 7.450 0.998 − 15.016 15.052 (mm) Post-immediate −24.564 * 6.923 0.001 − 38.536 − 10.592 7 days −57.945 * 6.517 <0.001 − 71.098 − 44.793 15 days −78.023 * 6.892 <0.001 − 91.932 − 64.113 Mean Pressure Baseline 13.638 17.699 0.445 − 22.080 49.356 (g/cm2) Post-immediate −1.836 16.789 0.913 − 35.717 32.045 7 days −5.280 16.415 0.749 − 38.406 27.846 15 days −6.623 16.735 0.694 − 40.394 27.149 Mean COP X Baseline −0.855 1.727 0.623 −4.339 2.630 Post-immediate −1.600 1.704 0.353 −5.039 1.839 7 days −1.255 1.578 0.431 −4.439 1.930 15 days −1.091 1.557 0.487 −4.232 2.051 Mean COP Y Baseline −1.695 1.143 0.145 −4.001 0.610 Post-immediate −3.477 * 0.958 0.001 −5.410 −1.545 7 days −4.259 * 0.874 <0.001 −6.022 −2.496 15 days −4.486 * 0.913 <0.001 −6.330 −2.643 Mean Anterior Velocity Baseline 0.077 0.089 0.390 −0.102 0.257 (mm/s) Post-immediate −0.045 0.073 0.535 −0.192 0.101 7 days −0.118 0.068 0.088 −0.255 0.018 15 days −0.077 0.080 0.342 −0.240 0.085 Mean Lateral Velocity Baseline −0.082 0.053 0.131 −0.189 0.025 (mm/s) Post-immediate −0.145 0.076 0.062 −0.299 0.008 7 days −0.136 0.083 0.106 −0.303 0.030 15 days −0.155 0.078 0.053 −0.311 0.002 * Indicates significant differences; EG: Experimental Group; CG: Control Group; CI: Confidence interval; SEM: Standard error of the mean; COP: Center of pressure. 3.2.2. 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