| Objective:According to traditional Chinese medicine (TCM), Hegu is a commonly used acupoint for treating disorders of head and face. However, improper operation at this point can cause severe mechanical and chemical nerve injury, resulting in hand motor dysfunction. For example, point injection, if the injection needle strays into arteries, can cause thrombosis obliterans, hemorrhage, or arterio-venous leak, followed by deficient blood supply of tissues, leading to muscle degeneration, or contracture. This study used multi-level dissection and blood vessels casting techniques to have multi-angle observation and measurement of the relationship between the morphology and the location of Hegu, in the hope to provide guidance for clinical practice in terms of the direction and depth of needle insertion, hence avoiding adverse effects of acupuncture. Studies both at home and abroad on the morphology of acupoints are under way, but so far morphological characteristic of acupoints is uncertain. Most scholars believe that acupoints should represent a spatial integration of a wide variety of structures and tissues. Therefore, this study not only provides research data for the guidance for clinical practice but also for the establishment of three-dimensional morphology of acupoints. Object and Methods:10 non-deformed hand specimens obtained from 5 fresh cadavers and 20 hand samples without deformity obtained from 10 formalin fixed adult cadavers underwent gross anatomical and casting operations.1. For formalin-fixed adult upper limb specimens, a needle was inserted and left at the location of Hegu point. Then, level by level anatomical operations were made to show important structures and tissues at different levels, focusing on the distribution of median nerve back branch, radial nerve superficial branch, deep branch of ulnar nerve and its terminal segment. Results are indicated by Mean±SD.2. For fresh upper limb, vascular casting was implemented by alkali-chip corrosion layer by layer and alkali and acid corrosion respectively to measure the distance between the skin point where the needle was inserted and the end of the radial artery, as well as the maximum angle and depth of the needle insertion when the needle reached the deep palmar arch.3. Data were analyzed by statistical software with p> 0.05 indicating that the difference was not statistically significant.Results:1. Gross anatomy of Hegu point: at the subcutaneous level, at the radial side lies the start part of vein radialis; at the ulnar side are the hand back vein network and the superficial branch of radial nerve. At the deeper level are the first dorsal interosseous muscle and adductor muscle of thumb; at the radial side thumb main arteries and recurrent branch of median nerve; at the ulnar side is deep branch of ulnar nerve accompanied by deep palmar arch.2. In light of the distribution of nerves and blood vessels in the location of Hegu point as demonstrated by gross anatomical and casting methods, we suggest that when the needle is inserted, the thumb should be stretched. The depth of the insertion of the needle should not exceed half the distance between the skin needling point and the skin of the palm. It will be safer if the needle is inserted straight or in the direction of Laogong and Houxi.3. Difference between left and right hand groups was not statistically significant (p> 0.05)4. In this study, we did not find significant difference between right and left hand groups but considerable differences across individuals.Discussion:1. Hoku is commonly used for treating craniofacial diseases. In recent years, injection therapy in this point is extensively carried out. However, improper manipulation of the needle can cause severe mechanical and chemical nerve injury, causing the hand motor dysfunction. For example, point injection, if the needle strayed into arteries, may cause vascular thrombosis inflammation, bleeding, or arterio-venous leak and so on, thus giving rise to muscle degeneration and contracture due to deficient blood supply of muscle. This study used multi-level dissection and blood vessels casting techniques and demonstrated the distribution of important structures and tissues in the location of Hegu, in order to provide relevant evidence for clinical use of this point in terms of depth and direction of needle insertion and hence prevent needle-induced adverse effects. On the other hand, morphological studies on acupoints have not come to any conclusions on the essence of acupoints. Findings form this study will greatly contribute to the establishment of three-dimensional morphology of acupoints.2. According to the findings from this study, the needle should be inserted straight in Hegu point. The average thickness between the skin of hand back and palm is 3.50±0.20cm, whereas the average thickness from the dorsum of the hand to the palm side of thumb adductor muscle is 2.68±0.27cm. This suggests that the depth of the needle insertion in Hegu should be no more than half the thickness between the skin point where the needle in inserted and the skin of palm. Importantly, the needle should be inserted straight. Drug injection should be shallow, and the needle should be inserted as far as possible away from important structures. Drugs should be in small dose, mild in nature, and easy to be absorbed.3. There are much domestic and foreign research on Hegu morphology, but the most commonly used is gross anatomical methods. This study used blood vessel casting, which is technically mature and provides accurate measurement.4. In this study, we observed a case of variation of the radial artery, which implicated that the needle insertion in this point should be careful and the magnitude of needle manipulation in this point should be mild.Conclusion:1. The morphology of Hegu is, from superficial to deeper levels, the skin, the subcutaneous tissue, the first dorsal interosseous muscle and adductor muscle of thumb.2. There is no significant difference between the morphological data of the left and right Hegu.3. the depth of the needle insertion in Hegu should be no more than half the thickness between the skin point where the needle is inserted and the skin of palm. Importantly, the needle should be inserted straight. Drug injection should be shallow, and the needle should be inserted as far as possible away from important structures. Drugs should be in a small dose, mild in nature, and easy to be absorbed.4. Vascular casting is a clear and definite manner to study the morphology of acupoints, thus can be used as an important means for morphological study of acupoints.
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