most cited clinical trials published between 1995 and 2018, and the 15 most recent studies included in high impact journals (first quartile of the Journal Citation Reports in the year of publication of the study), which assessed any therapy for subjects suffering from NP. Those articles with any of the following characteristics were excluded: NP patients with only a traumatic, surgical, or neurological origin for the condition; study protocols for clinical trials; studies including only elderly adults (older than 65 years), or including adolescents or children (younger than 18 years); or a lack of a clear description of the eligibility criteria. All relevant titles were saved in a reference manager (EndNote®, version X8.2, Thomson Reuters). Two researchers (C.G.-G. and Á.O.-P.-V.) independently performed the assessment of the studies in a blinded and standardized manner, taking into account the eligibility criteria previously set out. In the case of a disagreement, the issue was discussed together with a third member of the research team (A.M.H.-R.) until a final consensus was reached. 2.3. Assessment of the Methodological Quality The Physiotherapy Evidence Database (PEDro) scale score was used to assess the methodological quality of the clinical trials. The PEDro scale is an 11-item tool where items are scored as either absent (0) or present (1), except for item 1 that refers to external validity of the study. A final score from 0 to 10 is given. The PEDro scale is a valid [27] and reliable [28] tool to rate the methodological quality of clinical trials. A cut-off of at least 5 or 6 points is required for a study to be of adequate quality [29]. PEDro scores were extracted from the PEDro database. Two independent raters (J.C.F.-D. and A.F.-G.) evaluated, with the PEDro scale, those trials not included in the PEDro database. A final consensus about the final score was reached, together with a third member of the research team (A.M.H.-R.), whenever necessary. 2.4. Data Extraction Once the studies were selected, two authors (C.G.-G. and J.O.-P.-V.) independently retrieved the following information from each article following a standardized form: the number of authors affiliated with a clinical institution, e.g., hospital, private practice, or health-center, and the number affiliated with a non-clinical institution, e.g., a university or research center; total number of citations Diagnostics 2019, 9, 186 4 of 23 in the Web of Science; the PEDro scale score; aims of the study; sample size and characteristics of participants (distribution by sex, mean age and pain duration); and eligibility criteria (inclusion and exclusion criteria). Data collected from the studies we included were pooled into tables. 3. Results 3.1. Study Selection The search strategy resulted in a total of 309 relevant articles that were retrieved through the Web of Science database. Then, 94 studies were excluded for not matching the eligibility criteria. From the remaining 215 articles, 30 of them were finally included. All selected studies were written in English. Two of the top 15 most cited articles were excluded and replaced by the next most cited clinical trials in the list. The reason was that the sample population and the eligibility criteria used were the same as in other studies with a higher number of citations that were published by the same research groups and that had been already included for further analysis. Figure 2 shows the flow diagram for the study selection process. Diagnostics 2019, 9, x FOR PEER REVIEW 4 of 24 3. Results 3.1. Study Selection The search strategy resulted in a total of 309 relevant articles that were retrieved through the Web of Science database. Then, 94 studies were excluded for not matching the eligibility criteria. From the remaining 215 articles, 30 of them were finally included. All selected studies were written in English. Two of the top 15 most cited articles were excluded and replaced by the next most cited clinical trials in the list. The reason was that the sample population and the eligibility criteria used were the same as in other studies with a higher number of citations that were published by the same research groups and that had been already included for further analysis. Figure 2 shows the flow diagram for the study selection process. Figure 2. Flowchart diagram of the study selection process (Preferred Reporting Item for Systematic Reviews and Meta-Analyses, PRISMA, guidelines). Q1, first quartile; JCR, Journal Citation Reports. 3.2. Study Characteristics All of the clinical trials which were included were randomized and controlled. Detailed descriptions of articles included in this systematic review are presented in Table 1; Table 2. Researchers from non-clinical institutions authored more than 90% of the studies (28 out of 30), while authors from clinical institutions, e.g., hospitals, health-centers, and private practices, participated in 79% of trials (21 out of 30). The studies included a total of 4467 participants, with females representing 67.5% of the total (3017 females). One clinical trial did not clearly specify the sex distribution of the study sample [30]. Two studies recruited exclusively females [31,32], and only two of them selected more male than female individuals [33,34]. The mean age of participants was between 35 and 53 years, with one study including younger participants (mean age of 21 years) [35]. 3.3. Methodological Quality of Studies The assessment of the methodological quality by means of the PEDro scale revealed that, in general, the top 15 most cited clinical trials denoted adequate to good methodological quality, with a finalscoreofsixpointsorhigherexceptforonestudythatscoredfieoutof10points(Table1)[36]Figure 2. Flowchart diagram of the study selection process (Preferred Reporting Item for Systematic Reviews and Meta-Analyses, PRISMA, guidelines). Q1, first quartile; JCR, Journal Citation Reports. 3.2. Study Characteristics All of the clinical trials which were included were randomized and controlled. Detailed descriptions of articles included in this systematic review are presented in Table 1; Table 2. Researchers from non-clinical institutions authored more than 90% of the studies (28 out of 30), while