Final answer:
The correct distance to the spinal canal when needling DU-14 (da zhui) is typically between 0.5 to 1.0 cun. This depth ensures patient safety due to the proximity of major acupuncture points to critical body structures, particularly the spinal canal.
Step-by-step explanation:
The distance of the spinal canal from the skin surface when needling DU-14 (da zhui) can vary based on individual anatomy. However, traditionally it is said that the depth should be no more than 0.5 to 1.0 cun to avoid any potential harm, such as puncturing the spinal canal. Since DU-14 is located below the spinous process of the seventh cervical vertebra, the practitioner should be cautious and have a thorough understanding of anatomy and needling techniques while performing acupuncture in this area. Extra care must be taken not to insert the needle too deeply because major acupuncture points are connected to critical body structures, and DU-14 is closely related to the spinal canal and essential bodily functions. It is noteworthy that there are variations in anatomy, and the actual distance to the spinal canal can be different for each person. Therefore, correct acupuncture practice should always consider individual variations and employ techniques that ensure the safety of the patient.