Effectiveness of Dry Needling in Chronic Neck Pain.

All groups will be instructed by a physiotherapist in the performance of protocol of neck-shoulder exercises. This program will be carried out at home for at least three days a week during three months. The exercise protocol includes active mobilization, stretching and strengthening (concentric/eccentric, isotonic, and isometric) exercises. All participants will be given a booklet with a detailed description of every single exercise.

Those participants included in any of the DN groups will undergo 3 sessions of treatment (1 session per week during 3 consecutive weeks). In each session, the physiotherapist in charge of the intervention will assess the presence of active or latent MTrPs in severa neck shoulder muscles. The selected muscles have been previously described as having a higher prevalence of MTrPs in adults with chronic neck pain: a) scalene muscles; b) levator scapulae; c) splenius cervicis; d) cervical multifidus; and e) upper trapezius trapezius. The location of the trigger points will be carried out following the recommendations and guidelines described in the literature.

Those in the TE + local DN group will receive deep DN, using a fast-in fast-out technique, as described by Hong. The needle, once inserted in the muscle with a 10 to 20 mm depth, will be mobilized in a quick ascending and descending motion, in order to evoke the so-called LTRs. A minimum of 3 to 6 LTRs will be elicited in each muscle.

For patients in the TE + distal DN group, the deep DN intervention will be carried out in those muscles with MTrPs, but at a remote location from the MTrP area. The same evaluation and intervention protocol previously described for the TE + local DN group will be carried out. The main difference is that, in this group, DN will not elicit LTRs. Instead, DN will be applied at a minimum distance of 1-1.5 cm from the MTrP locus.

Finally, in the TE + placebo DN group, the therapeutic exercise program will be combined with DN using using a Dong Bang placebo needle, similar to the Streitberger placebo needle. These needles are designed with a retractable system. Therefore, these placebo needles evoke mechanical stimulation without piercing the skin; hence, patients experience a pressure sensation similar to that of a "real" needle.

Inclusion criteria

• Diagnosis of non-specific mechanical neck pain.
• Pain lasting for more than 3 months of duration.
• Self-reported pain higher than 3 in the Numeric Pain Rating Scale.
• Self-reported neck disability higher than 5 in the Neck Disability Index.

Exclusion criteria

• Absence of pain during passive neck rotation.
• Higher pain intensity in neutral position than during passive neck rotation.
• Absence of ipsilateral pain during passive neck rotation.
• Previous history of surgery of the cervical spine or upper extremity.
• Previous history of whiplash, diagnosis of fibromyalgia, or any neurological, inflammatory or rheumatological disease.
• Presence of two or more positive signs indicative of neural compression (sensitivity disorders, myotomic weakness in the upper extremities, or alteration in deep tendon reflexes).
• Radiological signs of root compression or spinal stenosis.
• Having received physical therapy treatment in the month prior to the start of the study.
• Analgesic and / or anti-inflammatory treatment in the last 72 h.
• Diagnosis of psychiatric disorders with ongoing medical treatment.
• Pregnancy or breastfeeding.
• Pending litigation in progress.
• Any contraindication to the use of dry needling.