The purpose of the trial is to evaluate whether patients with acute non specific neck pain get pain free sooner, if treated with subcutaneous carbon dioxide insufflations compared to sham ultrasound.

Subcutaneous carbon dioxide insufflations popular in Central und Eastern Europe are a safe and inexpensive treatment modality in complementary medicine and are used mainly in musculoskeletal pain and vascular conditions. However, no rigorous trial exists on their efficacy.

The study is designed as a double blind sham controlled randomized trial to evaluate whether patients with acute non specific neck pain get pain free sooner, if treated with subcutaneous carbon dioxide insufflations compared to sham ultrasound.Since acute non specific neck pain is often self limiting, speed of recovery rather than outcome at fixed points in time is evaluated.

Participants receive either a maximum number of 9 subcutaneous carbon dioxide insufflations or a maximum number of 9 sham ultrasound administered by 4 therapists in a randomized order, thrice weekly. Carbon dioxide gas is insufflated subcutaneously at the locations of neck muscle tenderness. Per tender location 25 ml carbon dioxide gas is administered.

Primary outcome measure is recorded daily by means of a diary. Analysis is done by intention to treat. Differences in time curves are tested using the logrank test. Time curves are graphically displayed by a 1 minus survival Kaplan-Meier plot.

Inclusion Criteria:

• participants must report neck pain lasting for less than 7 days
• participants must report a current pain intensity of ≥ 40 mm on a 100 mm visual analogue scale.
• participants must state local neck muscles tenderness during clinical examination at one or more locations

Exclusion Criteria:

• neck pain of specific etiology (e.g., radiculopathy, infection, inflammation, primary tumor, or metastases)
• whiplash injury
• former neck surgery
• pregnancy
• breast feeding.