Trial design
The trial design is a randomized, controlled, parallel, double-blind, three-arm clinical trial of treatment.
Hypothesis
Experimental treatments have a greater beneficial effect on disability and pain of subjects with NCNP than sham treatment.
Sample selection
Individuals with NCNP were recruited through a text message broadcast on social networks in the city of Seville and were selected based on the eligibility criteria listed below. The study was carried out in facilities of the physiotherapy department of the University of Seville.
Inclusion criteria
Exclusion criteria
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Irradiated neck pain
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Neck pain associated with vertigo
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Osteoporosis (Rx Control)
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Diagnosed psychological disorders
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Vertebral fractures (Rx Control)
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Tumors (Rx Control)
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Diagnosed metabolic diseases
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Previous neck surgery
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Red flags (night pain, severe muscle spasm, loss of involuntary weight, symptom mismatch)
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Physiotherapeutic treatment continued in the last 3 months
Interventions
The participants could only receive the assigned treatment; they could not combine the treatment with drugs or other physiotherapeutic treatment. Any interference in the treatment was a reason for exclusion. The participants were warned that if they took any medication, they would be excluded; they were asked in all evaluations about the use of any type of medication.
Group 1: Manual therapy
“Manual therapy” protocol was composed of three techniques based on scientific evidence for the treatment of neck pain [12,13,14,15].
This protocol was applied in the three treatment sessions, one per week.
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1.
High thoracic manipulation on T4. Patients are positioned supine with their arms crossed in a “V” shape over the chest. The therapist makes contact with the fist at the level of the spinous process of T4 and blocks the patient’s elbows with his chest. Following this, he introduces flexion of the cervical spine until a slight tension is felt in the tissues at the point of contact. Downward and cranial manipulation is applied. If cavitation is not achieved on the first attempt, the therapist repositions the patient and performs a second manipulation. A maximum of two attempts will be allowed in each patient [12].
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2.
Cervical articular mobilization (2 Hz, 2 min × 3 series). The patient is placed on the stretcher in a prone position, placing both hands under his forehead. The therapist makes contact with his two thumbs on the spinous process of the patient’s C2 vertebra and performs grade III posteroanterior impulses at a speed of 2 Hz and for 2 min. There are 3 mobilization intervals with a minute of rest between each one of them [13].
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3.
Suboccipital muscle inhibition (3 min). With the patient lying supine, the therapist places both hands under the subject’s head, by contacting their fingers on the lower edge of the occipital bone, and exerts constant and painless pressure in the anterior and cranial direction for 3 min [14, 15].
Group 2: Therapeutic exercise
“Therapeutic exercise” protocol: this protocol is based on a progression in load composed of different phases: at first, activation and recruitment of deep cervical flexors [16]; secondly, isometric exercise deep and superficial flexors co-contraction [16], and finally, eccentric recruitment of flexors and extensors [16,17,18]. This protocol, as far as we know, has not been studied, but activation of this musculature during similar tasks to those of our protocol has been observed [16,17,18]. This protocol was taught to patients in the first session and was performed once a day during the 3 weeks of treatment, 21 sessions in total. It was reinforced by the physiotherapist in each of the three individual sessions.
Week 1: Exercises 1 and 2.
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1.
Cranio-cervical flexion (CCF) in a supine position with a towel in the posterior area of the neck (3 sets, 10 repetitions, 10 s of contraction each repetition with 10 s of rest).
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2.
CCF sitting (3 sets, 10 repetitions, 10 s of contraction each repetition with 10 s of rest)
Week 2: Exercises 1, 2, 3, and 4.
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3.
Co-contraction of deep and superficial neck flexors in supine decubitus (10 repetitions, 10 s of contraction with 10 s of rest).
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4.
Co-contraction of flexors, rotators, and lateral flexors. The patients performed cranio-cervical flexion, while the physiotherapist asked him/her to tilt, rotate, and look towards the same side while he/she opposes a resistance with his/her hand (10 repetitions, 10 s of contraction with 10 s of rest).
Week 3: Exercises 1, 2, 3, 4, 5, and 6.
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5.
Eccentric for extensors. With the patient seated, he/she should perform cervical extension. Then, he/she must realize a CCF and finish doing a cervical flexion (10 repetitions).
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6.
Eccentric for flexors. The patients, placed in a quadrupedal and neutral neck position, should perform neck flexion; then, they must have done a cranio-cervical flexion and, maintaining that posture, extend the neck and then finally lose the CCF (10 repetitions).
Group 3: Sham treatment
For the “control” protocol, the patients were placed in the supine position, while the physiotherapist placed his hands without therapeutic intention on the patient’s neck for 3 min. The physiotherapist simulated the technique of suboccipital inhibition [14]. Later, with the laser pointer off, patients were contacted without exerting pressure for 10 s. Patients assigned to the control group received treatment 1 or 2 after completing the study.
Outcomes measures
As dependent variables of the study, we took pain, based on the visual analog scale (VAS) and the pressure pain threshold (PPT), and cervical disability, through the Neck Disability Index. VAS is a representative element of the perception of pain part of the subject; however, PPT focuses on a more objective part of pain; the combination of both gives us a great approximation to the actual measurement of pain, this being one of the elements more complex to reflect. The Neck Disability Index (NDI) allows us to obtain a very complete percentage of functionality/disability, since it includes multiple activities of daily life in its index.
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Neck Disability Index. The NDI is a self-assessment instrument of the specific functional status of subjects with neck pain with 10 elements that include pain, personal care, weight gain, reading, headache, concentration, work, driving, sleeping, and leisure. Each section is rated on a scale of 0 to 5, where 0 means “painless” and 5 means “the worst pain imaginable.” The points obtained are added to a total score. The questionnaire was interpreted as a percentage. The disability categories for NDI are 0–8%, without disability; 10–28%, mild; 30–48%, moderate; 50–64%, serious; and 70–100%, complete [19, 20].
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Visual analog scale for pain. The subjects participating in the study indicated the intensity of their pain by means of the VAS of 100 mm; they had to signal in a horizontal line of 100 mm where they would place their pain, being 0 mm “no pain” and the 100 mm “the worst pain imaginable” [21].
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Pressure pain threshold. The PPT was recorded in Newton/cm2 using digital algometer (Force Ten™ -Model FDX, Wagner, Greenwich, USA) with a surface area of round tip of 1 cm2. The measurement was taken on the spinous process of vertebra C2, the evaluator gradually increasing the pressure until the patient indicated through a “yes” when the pain or discomfort appeared. Three measurements were made, obtaining an average value of these three measurements for the statistical analysis [22, 23].
These variables were measured in the pre-evaluation, first evaluation (week 2), second evaluation (week 4, short-term), and third evaluation (week 12, medium term). These evaluations were carried out by an evaluator trained in these procedures; the data was stored in an Excel document.
Sample size calculation
The sample size was calculated using the Granmo calculator v.7.12, based on the analysis of the variance of means, and estimating an alpha risk of 5% (0.05), a beta risk of 10% (0.10), in a unilateral contrast, a typical deviation of 12% (0.12), a minimum difference to detect of 13.5% (0.135) which is based as the minimum clinically important differences in VAS [24], and a rate of follow-up losses of 8%, for which 20 subjects are required in each group, assuming that there are three groups. Finally, we included 69 patients who were divided into three groups, each group of at least 20 subjects, being able to overcome this value to assume the possible loss of follow-up.
Randomization
Subjects were divided into three groups by means of balanced randomization, performed with free software (http://www.randomized.org/). The randomization sequence was only known by the principal investigator and auditor.
Blinding
Evaluator and participants in the study were blinded during the entire process. The evaluators were unaware of the study objectives and the allocation of patients in the study groups. The patients did not know the group to which they belonged. The sequence of randomization was hidden from the evaluators and the patients, and this sequence was kept by the main researcher throughout the study and was not available to the rest of the participants involved in the trial.
Statistical analysis
The statistical analysis was carried out through the IBM-SPSS Statistics 24 software. The normality test applied to all the variables was Kolmogorov-Smirnov test. For the contrast of intragroup hypotheses, Student’s T test for paired variables was applied in the case of parametric distributions and Kruskal-Wallis H for non-parametric distributions. For the intergroup hypothesis contrast, one factor ANOVA will be used in the case of parametric distributions and Kruskal-Wallis H for nonparametric distributions. Post-hoc analysis was obtained through Bonferroni’s contrast for parametric distributions and Mann-Whitney’s U for nonparametric ones. The confidence level used will be 95% (0.05) and the power of the study will be 90% (0.1). Size effect was calculated through eta squared, where the values of r2 have been considered as 0.01 (small), 0.06 (medium), and 0.14 (large). Principles of intention to treat were not applied.