How accurate is the cun measurement?

The Accuracy Of The Cun Measurement

Locating acupuncture points accurately is imperative for successful research and treatment outcome (Bailey 2018).

The cun measurement

There are two methods of point location generally used in traditional Chinese medicine, which are directional (finger cun Fig 1.) and proportional (bone cun Fig 2.) measurements. The finger cun (F-cun) unit of measure was devised by a famous physician, Sn Su Mo, who lived between AD581 and 673. He recognised that his patients came in different shapes and sizes and to use a standard measurement for all of them was not logical. Therefore, he used the distance between the creases of the distal and middle phalangeal folds, when the patient’s finger was flexed, as a measure.

Figure 1.Illustration showing finger cun measurements (copyright Steve Bailey 2018)

This modular “inch” is called the cun or pounce (Ellis 1994). Since this time other relative measurements on the human body has been presented, for example the length from the elbow crease to the wrist crease is believed to be 12 cun, and the centre of the patella to the lateral extremity of the lateral malleolus is suggested to be 16 cun and is referred to as the bone cun (B-cun) measurement system. However, it is important that we understand that the cun was designed over 2000 years ago on a specific, Asian population and in current day practice may not be suitable for a multicultural population. For example, body segment parameter has been suggested to differ from specific population groups such as elderly male population (as observed in cadaver studies) may differ substantially from other sub groups, such as young adult females or children (Pearsall and Reid 1994). Lee et al (2014) found a clear ethnic difference in body size, proportion, and composition in the population they assessed.  Even within an ethnic group (e.g. South Asian) and ethnic sub-groups such as Indian, Pakistani, and Bangladeshi, there are substantial differences in anthropometric measurements (Whitrow and Harding 2008).

Figure 2.Illustration showing bone cun measurements (copyright Steve Bailey 2018)

In general, Afro-Caribbean/African-American have a greater bone mineral density and body protein content than do Caucasian. Furthermore, there are racial differences in the distribution of subcutaneous fat and the length of the limbs relative to the trunk (Wagner and Hayward 2000). Analysis of cadavers by Merz et al (1956) and Seale (1959) found that the bones of the extremities are relatively longer in Afro-Caribbean/African-American than in Caucasian. Afro-Caribbean/African-American on average, have shorter trunks and longer extremities than Caucasian (Malina 1973, Malina 1996, Bouchard 1996).

Yin et al (2005) found the F-cun measurements were significantly different from the B-cun measurements and varied significantly according to the arbitrarily selected F-cun standard. In addition, they observed further differences of F-cun measurements in the extremities of obese subjects. They suggested that differences in results may depend upon racial physiological differences between Europe and Asia. They concluded that the F-cun method is unreliable and that further research should be conducted to determine a more accurate point-locating method primarily based on the B-cun method. Aird et al (2002) found no significant difference between the F-cun and B-cun (traditional) methods and that contemporary (elastic and ruler) methods that was observed was significantly more accurate than traditional methods. It is important to note that this study was not on different populations and the overall findings was that both methods was inaccurate.

Clinical implications of cun measurement

The cun measurment system should be used as a guide and not as a precise tool of measuring body segments on individuals. It should be used to assist the practitioner to locate the approximate location of an acupoint more quickly before palpating to find the precise location of the acupoint (Bailey 2018).

If you would like to learn more about how to locate acupuncture points, you can take a look at my video here:

Palpation skills

Palpation skill are important. When teaching physical therapists how to locate acupuncture points, I find that they tend to press too firmly, which I must admit this is something that I use to do myself. It is important that not too much pressure is applied when trying to locate an acupuncture point because if the pressure is too firm it will obliterate the point and make it difficult to locate.

This can be a problem to physical therapist when they first start to practice acupuncture because they are used to palpating deep into soft tissue to locate the underlying structure and feel for nodules, crepitus, tightness, etc.

When palpating acupuncture points you need to use your index or middle finger and run it gently over the surface of the skin in the region of the point feeling for a depression, sensitivity, changes in the temperature of the skin, nodules, sponginess and change in smoothness in which the finger glides over the skin. You will find that once you get close to or over an acupuncture point the finger will start to drag or it does not glide as smoothly. Once you pass the acupoint your finger will start to glide more smoothly again.

During palpation, you will find that some points are sensitive and tender (reactive) particularly when requiring treatment. When treating musculoskeletal (MSK) conditions you will find reactive points such as Liv-3 that will be tender when there is a muscle tear anywhere in the body and may only be tender on the side in which the tear is located. GB-41 may be tender to palpate when there is a muscle spasm, tear, or pronounced muscular weakness along the course of the Gall Bladder meridian. For example, in cases of low back pain where there is active TrPs in the quadratus lumbarum, gluteus medius or minimi referring pain down the lateral side of the hip and leg. Throughout your treatment these points should be assessed, and you will find that as the condition improves the tenderness of these points will subside.

 

References

  1. Bailey SD (2018). Dry needling and traditional Chinese acupuncture. Manual of acupuncture points, trigger points and auricular points for the management of musculoskeletal and associated disorders. ISBN 978-1-916430303.
  2. Ellis, N. (1994) Acupuncture in Clinical Practice: A guide for healthcare professionals. London: Chapman and Hall.
  3. Pearsall, D., and Reid, J.G. (1994) The study of human body segment parameters in biomechanics. An historical review and current status report. Sports Med. 18(2): 126–140.
  4. Lee, S., Bountziouka, V., Lum, S., Stocks, J., Bonner, R., Naik, M., Fothergill, H., Wells, J. (2014) Ethnic variability in body size, proportions and composition in children aged 5 to 11 years: Is ethnic-specific calibration of bioelectrical impedance required? POLS. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0113883#s3.
  5. Whitrow, M.J., Harding, S. (2008) Ethnic differences in adolescent lung function: anthropometric, socioeconomic, and psychosocial factors. Am J Respir Crit Care Med 177: 1262–1267. doi: 10.1164/rccm.200706–867oc.
  6. Wagner, D., and Heyward, V. (2000) Measures of body composition in blacks and whites: a comparative review. Am J Clin Nutr, 71: 1392–402.
  7. Merz, A.L, Trotter, M., Peterson, R.R. (1956) Estimation of skeleton weight in the living. Am J Phys Anthropol, 14: 589–609.
  8. Seale, R.U. (1959) The weight of the dry fat-free skeleton of American whites and Negroes. Am J Phys Anthropol, 17: 37–48.
  9. Malina, R.M. (1973) Biological substrata. In: Miller K.S., Dreger R.M., eds. Comparative studies of blacks and whites in the United States. New York: Seminar Press, pp. 53–123.
  10. Malina, R.M. (1996) Regional body composition: age, sex, and ethnic variation. In: Roche, A.F., Heymsfield, S.B., Lohman, T.G. eds. Human body composition. Champaign, IL: Human Kinetics, pp. 217–55.
  11. Bouchard, C. (1996) Genetic influences on human body composition and physique. In: Roche, A.F, Heymsfield, S.B., Lohman, T.G. eds. Human body composition. Champaign, IL: Human Kinetics, pp. 305–27.
  12. Yin, C., Park, H., Seo, J., Lim, S., Koh, H. (2005) Evaluation of the cun measurement system of acupuncture point location. Am J Chin Med, 33(5): 729–35.
  13. Aird, M., Cobbin, D., Rogers, C. (2002) A study of the relative precision of acupoint location methods. The Journal of Alternative and Complementary Medicine, 8(5): 635–642. doi:10.1089/107555302320825156

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