Blinding and Previous Experiences of Dry Needling

Dry needling (DN) is a treatment technique widely used in patients with various musculoskeletal health problems due to myofascial trigger points (MTrP). DN has shown to have positive effect on pain and function in patients with mechanical neck pain. These positive results are thought to be the consequence of specific neurophysiological and mechanical processes. Research has shown that DN induces 1) end plate inhibition, 2) reduction of inflammatory substances, 3) increase of blood flow and oxygen and 4) a reduction of nociceptive afferent activity. However, the exact working mechanisms underlying DN effects is still a topic of debate. This trial addresses one of the major methodological issues in needle testing,the effects of proper blinding. DN is a specific technique that is not easily be replaced by another comparable intervention. A sham needle with a blunt tip was created that simulates penetration into the skin without actually doing so. Research about a valid method for the control in needling studies is for this reason of particular relevance. A proper blinding technique is of importance to further the field of DN.

The objectives of this study are to analysize short-term effects on pain intensity and pressure pain sensitivity according to previous experience (blinding) in subjects with mechanical neck pain receiving real or sham-DN and to determine the success in masking DN versus sham DN in patients with mechanical neck pain based on prior experience with this technique.

The intervention group will receive real dry needling (DN) (fast in and fast out needling technique) in an active MTrP within upper trapezius muscle.

The placebo group will receive sham needling in an active MTrP within the upper trapezius muscle. A sham needle will be used as placebo. This needle has a blunt tip and retractable handle that created the illusion of a needle penetrating the skin.

Real dry needling will be conducted according to Hong description, fast-in and fast-out interventions. The intervention will be applied until a total of four local twitch responses will be elicited

Sham dry needling with be conducted with a sham needle (Steitberger's Park sham device (PSD). This needle has a blunt tip and retractable handle that created the illusion of a needle penetrating the skin. When this needle touches the skin, a pricking sensation will be created. However, when pressure will be increased, the shaft of the needle disappears into the handle creating a sensation on the patient.

The intensity of neck pain at rest and during active movement of the cervical spine in rotation will be assessed with a visual analogue scale (VAS).

Participants will be asked directly after the intervention whether they thought they had received a real intervention or a sham. Answering categories were: 'yes' (real DN) or 'no' (sham DN).

Pressure pain thresholds (PPT) will be assessed at the upper trapezius muscle, spinous process of C7 and distant pain-free area of the lower extremity (heel)

Patients self-perceived improvement will be assessed using a Global Rating of Change (GROC) consisting of a 15-point scale ranging from -7 (a very great deal worse) to +7 (a very great deal better). Descriptors of worsening or improving are assigned with values ranging from -1 to -7 and +1 to +7, respectively

Inclusion Criteria: Non-specific mechanical neck pain of at least 3 months of duration Between 18-60 years old At least one active trigger point in the upper trapezius muscle which referred pain reproduces the neck pain symptoms Exclusion Criteria: whiplash injury; previous cervical or thoracic surgery; cervical radiculopathy or myelopathy; diagnosis of fibromyalgia syndrome; having undergone physical therapy in the previous 6 months; fear to needles