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]. Diagnostics 2019, 9, 186 5 of 23 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 final score of six points or higher, except for one study that scored five out of 10 points (Table 1) [36]. Similar findings were observed amongst the 15 most recent articles published in high impact journals (Table 2), although one study denoted poor methodological quality (four out of 10) [37]. One of all studies included achieved excellent methodological quality (10 out of 10) [38]. The reliability between coders for those studies whose scores were not available in the PEDro database was almost perfect (Kappa = 0.84) [39]. Diagnostics 2019, 9, 186 6 of 23 Table 1. Top 15 most cited clinical trials about treatment efficacy in neck pain published between 1995 and 2018. NP, neck pain; Clinical, number of authors belonging to clinical institutions; Non-Clinical, number of authors belonging to academic institutions; SM, spinal manipulation; PT, physical therapy; GP, general practitioner. Study Authors’ Institutions Number of Citations PEDro Score Aim Participants (Sex and Mean Age) Inclusion Criteria Exclusion Criteria Ylinen et al., 2003 [32] Clinical: 5 Non-Clinical: 4 Citations: 285 7/10 Assess the efficacy of intensive isometric training and light endurance training in chronic NP N = 180 All females 46 years Females; aged 25 to 53 years; office worker; permanently employed; motivated to continue working and for rehabilitation; constant or frequently occurring NP > than 6 months Severe neck disorders, e.g., disk prolapse and spinal stenosis; postoperative conditions in the neck-shoulder; severe trauma; instability; spasmodic torticollis; frequent migraine; peripheral nerve entrapment; fibromyalgia; shoulder tendonitis, bursitis, or capsulitis; inflammatory rheumatic disease; severe psychiatric illness; diseases that prevent physical loading; pregnancy Cleland et al., 2005 [40] Clinical: 5 Non-Clinical: 0 Citations: 156 8/10 Evaluate the immediate effects of thoracic SM in chronic NP N = 36 27 females 9 males 35 years Aged 18 to 60 years; primary complaint of mechanical NP, defined as non-specific pain in the cervicothoracic region and exacerbated by neck movements Red flags for serious spinal conditions, e.g., infection, tumors, osteoporosis, fracture; positive signs or symptoms suggestive of nerve root involvement, e.g., altered upper limb reflexes, sensation, or strength; cervical or thoracic surgery; prior SM treatment; thoracic spine hypermobility; pregnancy Jordan et al., 1998 [36] Clinical: 3 Non-Clinical: 3 Citations: 152 5/10 Assess the effectiveness of intensive cervical training vs. PT vs. chiropractic treatment in chronic NP N = 119 88 females 31 males 39 years Aged 20 to 60 years; NP > 3 months with or without non-radicular pain; to live within a close distance to the hospital; X-ray examination of the cervical spine; to be able to speak and read Danish Acute NP with no freedom of movement; PT, SM, or training for the neck-upper extremity within 6 months; neuropathy; systemic disease; inflammatory joint or muscle disease; headache dominating over NP; migraine; hypermobility; whiplash; primary shoulder or upper extremity problems; previous neck surgery Irnich et al., 2001 [41] Clinical: 0 Non-Clinical: 10 Citations: 146 7/10 Compare the efficacy of acupuncture vs. massage combined with “sham” laser acupuncture in chronic NP N = 177 117 females 60 males 52 years Aged 18 to 85 years; chronic NP; painful restriction of neck mobility > 1 month; had not received any treatment in the previous 2 weeks Previous surgery, dislocation or fracture; neurological deficits; systemic disorders; contraindications to any of the applied treatments Diagnostics 2019, 9, 186 7 of 23 Table 1. Cont. Study Authors’ Institutions Number of Citations PEDro Score Aim Participants (Sex and Mean Age) Inclusion Criteria Exclusion Criteria Korthals-de Bos et al., 2003 [42] Clinical: 0 Non-Clinical: 9 Citations: 137 6/10 Evaluate the cost effectiveness of PT, manual therapy, and GP care for acute, subacute and chronic NP N = 183 121 females 62 males 45 years Aged 18 to 70 years; NP > 2 weeks (confirmed during physical examination); willingness to comply with treatment and follow up PT or manual therapy for NP in the previous 6 months; neck surgery; a specific cause for the NP (for example, malignancy, fracture, or inflammation) Cleland et al., 2007 [43] Clinical: 4 Non-Clinical: 2 Citations: 133 7/10 Compare the effect of thoracic nonthrust vs. mobilization/SM, and compare frequencies, side effects, and durations in acute and subacute NP N = 60 33 females 27 males 43 years Aged 18 to 60 years; a primary complaint of NP with or without unilateral upper-extremity symptoms; a baseline Neck Disability Index score ≥ 10% Signs suggestive of a non-musculoskeletal aetiology; whiplash within 6 weeks; cervical spinal stenosis; signs of nerve root compression (decrease of at least 2 of the following: myotomal strength, sensation, or reflexes); central nervous system involvement; previous cervicothoracic surgery; pending legal action Irnich et al., 2002 [44] Clinical: 0 Non-Clinical: 8 Citations: 127 6/10 Evaluate immediate effects of 2 different modes of acupuncture vs. sham procedure in chronic NP N = 34 25 females 9 males 52 years NP > 2 months; diagnosis of myofascial syndrome or irritation syndrome based on history, pain characteristics, radiological findings and manual examination Radicular