Guidelines to minimize risk when dry needling the rectus capitus posterior major muscle.

Background: Headache disorders are prevalent often leading to disability. The rectus capitus posterior major muscle (RCPMaj) may contribute to headache symptoms via nociceptive convergence and myodural bridging.

Objectives: To establish guidelines for needle length and needle angle to mitigate risks during dry needling RCPMaj.

Design: Cadaveric investigation.

Methods: Twenty-five cadavers (mean age: 80.1 ± 13.2 years) were placed in prone. Depth measurements from the skin to the C2 spinous process were taken following midline incision. Dissection continued exposing the RCPMaj for three measures including: 1) posterior angle from the frontal plane, 2) lateral angle from midline, and 3) distance from the external occipital protuberance to the lateral most RCPMaj.

Results: Mean values for tissue thickness overlying C2 spinous process (37 ± 7.3 mm), RCPMaj posterior angle from the frontal plane (65.2° ±10°), RCPMaj lateral angle from midline (34.7° ±12.9°), and distance from the external occipital protuberance to the lateral most RCPMaj (30.6 mm ± 9.3 mm) were used to calculate a needle inclination of ≤45° and a needle length <40 mm to reach the occipital portion of RCPMaj with an a priori insertion point of midway between the C2 spinous process and the C1 transverse process.

Conclusion: Inserting a dry needle <40 mm in length midway between the C2 spinous process and the C1 transverse process with a cranial angle of ≤45° relative to the frontal plane would increase the likelihood of reaching the RCPMaj and mitigate penetrating deeper structures.