In medieval times before modern measuring devices, systems were crude. In antiquity, there were measuring systems that were derived from the human body. The anatomical inch “cun” system has persisted for thousands of years in China and continues in practice to this day in various forms of Chinese medicine [1]. Trying to standardize this system of measurement is extremely challenging because there is a historical presence and a conventional use in practical clinical application [2,11]. There is also poor characterization between body dimension measuring methods between east and west modalities. In this study, acupoints Large Intestine 4 (LI4) and Large Intestine 6 (LI6) were located using a combination of anthropometric and the Chinese anatomical inch measurement (CUN) systems to determine accuracy and precision, verify the world health organization’s guidelines for the location of these acupoints, and to observe any variation in the location in male and female cadavers. By combining methods of directional (f-cun) and proportional (b-cun) measurements with anthropometric data, a range was found where LI4 and LI6 can be located in cadavers for more detailed research on specific structures.

Embalmed cadavers were used in this study instead of living participants because subsequent dissection can reveal underlying structures that may be involved in specific mechanisms associated with LI4 and LI6. There is also a need in the literature to characterize acupoints with underlying structures that may or may not cross more than one acupoint. Abreviations of anthropometric and cun measurements are found in Table 1, Table 2. Sixteen cadavers (7 female, 9 male; 14 Caucasian and 2 African American) were embalmed and processed according to the Environmental Health and Safety Department at the LSU Health Sciences Center (LSUHSC) in New Orleans and under Occupational Safety and Health Administration’s policy and guidelines. Cadavers were hyperperfused with a mixture of formaldehyde, glycerin, phenol, and water for long-term use in gross anatomy teaching courses. Prior to embalming, the age ranges for the cadavers were from 50 to 95 years old, with a mean age of 80 ± 12 years. The height ranges for the cadavers were 1.8 m to 1.5 m, with the mean height of 1.7 ± 0.1 m. The weight ranges for the cadavers were 81.6 kg to 45.4 kg, with the mean weight of 59.4 ± 12.3 kg. The BMI ranges for the cadavers were between 29.3 kg/m² to 15.2 kg/m², with the mean BMI of 21.4 ± 3.9 kg/m². A total of 25 hands and forearms were observed to determine the location of LI4 and LI6. Measured body dimensions were compared between male and female cadavers. Lastly, similar anthropometric and CUN body dimensions were compared and correlated to observe any relationship between them. Body dimensions and acupoint identification were collected in the gross anatomy laboratory facilities at LSUHSC.

References [3,4,5,6,7]..

&md=tbl&idx=1' data-target="#file-modal"">Table 1

Anthropometric measurements..

Dimension of anthropometric measurement	Abbreviation	Definition
Hand length	HL	The distance from the middle of interstylion to the tip of the middle finger
Index finger length	2DL	The distance from the proximal flexion crease of the tip of the index finger
Palm length	PL	The distance from the middle of interstylion to the proximal flexion crease of the middle finger
Hand breadth	HB	The distance from the most lateral point on the head of the 2D metacarpal to the most medial point on the head of 5D metacarpal
Index finger proximal breadth	2D2B	The distance from the most lateral point on the index finger proximal joint to the most medial point of the index finger proximal joint
Index finger distal breadth	2D1B	The distance from the most lateral point on the index finger distal joint to the most medial point of the index finger distal joint
Wrist breadth	WB	The distance from the most lateral point on the wrist to the most medial point of the wrist
Wrist depth	WD	The distance from the most anterior point on the wrist to the most posterior point of the wrist
Maximum hand breadth	MHB	The distance from the most lateral point on the head of the 1D metacarpal to the medial point on the head of 5D metacarpal with closing fingers
Hand thickness	HT	The distance from the back of the middle finger to the most medial point of the palm
Maximum hand thickness	MHT	The maximum distance from the back of the hand to the most projected point of the abductor policies brevis
Hand circumference	HC	The superficial distance around the edge of the metacarpals
Wrist circumference	WC	The superficial distance around the edge of the wrist
Maximum hand circumference	MHC	The maximum superficial distance around the edge of the hand with closing fingers
Little finger proximal circumference	5D2C	The superficial distance around the edge of the proximal joint in the little finger
first metacarpal bone	MC I	The distance of the first metacarpal bone from the proximal base to distal head
second metacarpal bone	MC II	The distance of the second metacarpal bone from the proximal base to distal head
Forearm (Elbow to wrist) length	FL	The distance from the olecranon process to the distal end of the styloid process of the ulna.
Maximum forearm circumference	MFC	The maximum circumference of the forearm perpendicular to its long axis.
Elbow breadth	EB	The distance across the medial and lateral epicondyles of the humerus
Elbow depth	ED	The distance between olecranon process of the ulna and the biceps brachii tendon in the cubital fossa

References [3,4,5,6,7]..

References [10,12,13]..

&md=tbl&idx=2' data-target="#file-modal"">Table 2

Chinese Anatomical inch measurements and acupoint locations..

Dimension of Chinese Inch Measurement	Abbreviation	Definition
Chinese anatomical inch site 1A	CUN 1A	Thumb width of the interphalangeal joint
Chinese anatomical inch site 1B	CUN 1B	Length between the skin creases of the middle phalanx of the middle finger
Chinese anatomical inch site 1.5	CUN 1.5	The width of the index and middle finger, measured at the level of the proximal interphalangeal joint of the index finger
Chinese anatomical inch site 2	CUN 2	the length of the distal and middle phalanges of the index finger
Chinese anatomical inch site 3	CUN 3	Width of all four fingers, measured at the level of the proximal interphalangeal joint of the index finger
Chinese anatomical inch site 4	CUN 4	Width of all four fingers, measured at the level of the metacarpophalangeal joint of the index finger
Chinese anatomical inch site 12	CUN 12	Length of transverse cubital crease to the transverse carpal crease
Distance along Large Intestine Meridian between LI5 and LI11	LI5 to LI11	Length between two anatomically distinct points from the depression at the lateral end of the transverse cubital crease and lateral epicondyle to the depression between the tendons of the extensor pollicis brevis and longus muscles (anatomical snuffbox) cun 12
Location of Large Intestine 4 Acupoint	LI4	On the dorsum of the hand, radial to the midpoint of the second metacarpal bone. Between the first and second metacarpal bones, approximately in the middle of the second metacarpal bone on the lateral side
Location of Large Intestine 5 Acupoint	LI5	On the posterolateral aspect of the wrist, at the radial side of the dorsal wrist crease, distal to the radial styloid process, in the depression of the anatomical snuffbox.
Location of Large Intestine 6 Acupoint	LI6	On the posterolateral aspect of the forearm, on the line connecting LI5 to LI11,3 B-cun superior to the dorsal wrist crease.
Location of Large Intestine 11 Acupoint	LI11	On the lateral aspect of the elbow, at the midpoint of (he line connecting I.U 5 with the lateral epicondyle of the humerus. When the elbow is fully flexed. LI11 is located in the depression on the lateral end of the cubital crease.

References [10,12,13]..

The author supervised all anthropometric and CUN measurements done by others [1,4,5,6,7,8,9]. The author is a licensed massage therapist, a certified practitioner in the American Organization for the Bodywork Therapies of Asia with 9 years of private practice experience, and a gross anatomist with over 10 years of teaching and dissecting experience. Two undergraduate students measured body dimensions with a Neiko Tools digital caliper (model 01408A, ∼0.01 mm) and a body measuring ruler sewing tailor tape measure (∼0.1 cm). The undergraduate students were a junior (third year) nursing student and a senior (fourth year) respiratory therapy student. Both students had taken an anatomy dissection course at LSUHSC prior to assisting in the research project. Each undergraduate student collected measurements for one cadaver at a time, which included the left and/or right sides. Each student never overlapped measurements with the other student on the same cadaver. Each anthropometric and CUN dimension was measured five times. The mean, standard deviation, and range of the sample group were calculated.

Subsequently, the author located LI4, LI5, LI6, and LI11 on each cadaver’s hand and forearm in accordance with the World Health Organization standards and textbook descriptions (Fig. 1) [10,12,13]. The second metacarpal bone (MC II) was outlined on the dorsum skin of the hand to locate LI4, and help visualize the acupoint. The author measured the MC II from the proximal base to the distal head in each hand by palpating the bone and using the caliper. At half the distance measured, the acupoint was located on the skin lateral to the middle lateral posterior border of the MC II. This point was marked with a black marker on the skin for visualization. Subsequently, the distance from marked LI4 acupoint to the proximal base and distal head of the MC II was measured. The author compiled and graphed the data to determine the approximate precision and accuracy in locating the acupoint. The mean, standard deviation, and ranges were calculated for LI4.

Figure 1. Location of LI4 on the posterior hand and LI6 on the pronated forearm in relation to bony structures along the large intestine meridian.

In order to locate LI6, the author first located LI5 in the depression of the anatomical snuffbox with the tendons of extensor pollicis longus and brevis muscles around the depression, and then LI11 at the lateral end of the transverse cubital crease anterior to the lateral epicondyle. LI5 was marked with a black marker on the skin in the depression where the radial styloid process could be palpated in the anatomical snuff box. LI11 was also marked with a black marker where the lateral extensor group muscles attached anteriorly to the lateral epicondyle. The author drew a straight line connecting LI5 to LI11. For each specimen, the width of all four fingers measured at the level of the proximal interphalangeal joint of the index finger or the millimeter equivalent of 3 CUN was used to locate LI6 on the line. The acupoint was identified and marked with a black marker.

Statistical analysis, correlations, and graph generation was done using Graphpad Prism software. Standard t-tests were done comparing body dimensions. Diagrams and selected figures were made in Adobe Photoshop 2020. Tables were made using Adobe InDesign 2020.

Several body dimensions were statistically significant between male and female cadavers (Table 3). Hand Length (HL), Maximum Hand Breadth (MHB), Hand thickness (HT), and the length between the skin creases of the middle phalanx of the middle finger (CUN 1B) were not significant between male and female cadavers (Table 3). Cun ratio measurements had no significant difference between male and female cadavers when calculated (not shown). The mean cun was calculated by dividing the millimeter equivalents of all CUN measurements to CUN 1A and then comparing them to traditional measurements. The variability mean cun (normalized to CUN 1A) and traditional cun measurements increased with the measuring distance (Fig. 2A).

* = 0.005, ** = 0.01, *** < 0.001..

&md=tbl&idx=3' data-target="#file-modal"">Table 3

Sex differences of anthropometric and cun measurements (mean and SD in mm)..

Item	Female (n = 12)			Male (n = 13)			T-Statistic	p
	Mean	SD	Range	Mean	SD	Range
HL	170.87	10.64	185.00–144.20	181.22	17.93	235 00–164 00	1.74	ns
2DL	65.72	7.66	81.66–58.51	76.41	12.84	109.52–63.22	250	*
PL	93.99	7.08	103 61–79.32	99 63	2.31	101 63–93 32	272	*
HB	70.80	3.99	76.19–61.58	79.36	5.44	89.22–/1.54	4.46	***
2D1B	14.46	1.24	16.36–12.73	17.86	1.19	19 58–15.87	7 00	***
2D2B	16.82	1.67	19.54–14.56	20.07	1.33	23.84–18.39	5.42	***
WB	47.94	5.49	55.92–34.73	56.92	3.49	64.24–51.38	493	***
MHB	81.09	11.11	100.11–63.98	86.76	9.77	101.44–68.14	1.36	ns
HT	24.40	5.65	33.98–14.58	27.24	5.38	36.09–19.33	1.29	ns
MHT	40.35	4.71	47.30–34.09	50.29	4.72	60.41–43.74	5.27	***
HC	181.47	11.46	199.20–157.60	212.35	9.84	230.60–199.60	7.25	***
WC	150.20	11.65	166.80–128.40	167.48	10.09	189.80–154.40	3.97	***
MHC	211.75	14.70	236 60–192 0	23892	1.49	267 20–219 20	447	***
5D2C	53.65	4.09	59.00–44.80	61.92	3.12	66.80–56.40	5.71	***
FL	246.78	9.68	264.60–225.80	26272	18.64	295.2–236 2	265	*
EB	66.77	7.10	78.17–53.36	77.70	8.39	103.32–72.17	3.50	**
MFC	220.17	24.01	256.6.–177.80	245.07	28.33	301.40–205.00	2.36	**
ED	64.22	8.63	77.00–52.56	74.51	12.31	101.34–62.19	240	*
WD	33.57	2.69	37.62–27.81	40.14	1.85	43.68–37.21	7.17	***
MC I	42.87	5.40	51.28–31.55	51.59	4.71	59 00–41.38	4 32	***
MCII	61.15	5.64	67.61–50.42	68.35	6.79	78.10–55.22	287	**
CUN 1A	17 86	1.22	1967–15.59	21 87	1.68	24 97–18 58	6 75	***
CUN 1B	21.24	3.58	28.06–16.18	23.71	3.72	33.41–19.26	1.62	ns
CUN 1.5	34.05	3.36	38.65–27.63	40.30	2.92	45.97–36.25	4.98	***
CUN 2	41.74	3.84	45.80–32.18	46.69	3.76	53.06–42.70	3.26	**
CUN 3	67.20	4.85	75.69–60.91	80.01	2.74	85.69–76.20	823	***
CUN 4	71.15	3.79	78.20–63.21	81.94	4.74	89.46–74.96	6.24	***
CUN 12	218.22	8.85	237.00–204.40	249.49	15.81	268.20–221 00	564	***
LI5 to LI11	215.08	19.85	239.00–171.00	241.42	17.66	280.00–214.00	3.51	**

* = 0.005, ** = 0.01, *** < 0.001..

Figure 2. Correlation of f-cun and Anthropometric measurement in locating LI4 and LI6. (A) Sample and traditional f-cun. Sample measurement has a degree of variability from traditional measurements as distance increases. (B) The approximate location of LI4 is between 50 mm to 23 mm, with the mean range between 36 ± 6 mm (distal head) to 30 ± 4 mm (proximal base) along the distance of the second Metc. (C) The approximate location of LI6 is between 201 mm to 61 mm, with a mean range between 156 ± 22 mm (from LI11) to 74 ± 8 mm (from LI5). (D) CUN 1A vs CUN 1B had a positive correlation, r(23) = 0.69, p = 0.0002. (E) HB and CUN 4 had a significant positive correlation between the two measurements, r(23) = 0.86, p = 0.0001. (F) FL vs CUN 12 had a significant positive correlation between the two measurements, r(23) = 0.73, p = 0.0001.

Between measured f-cun and calculated b-cun, 1.5 to 3 cun were significantly different. Thumb width of the interphalangeal joint (CUN 1A) and the width of all four fingers, measured at the level of the metacarpophalangeal joint of the index finger (CUN 4), were not statistically significant between measured f-cun and calculated b-cun (Table 4).

* = 0.05, ** = 0.01, *** < 0.001; ^† = CUN 1B was compared to B-cun 1..

&md=tbl&idx=4' data-target="#file-modal"">Table 4

Comparison of measured F-cun and calculated B-cun (Mean and SD in mm)..

F-cun measured			B-cun calculated measured from - CUN 12			p	Expected
Item	Mean	SD	Item	Mean	SD
CUN 1A	19.95	2.47	B-cun 1	19.50	1.70	ns	12X
CUN 1B †	22.52	3.79	-	-	-	**	12X
CUN 1.5	37.37	4.45	B-cun 1.5	29.10	2.30	***	8X
CUN 2	44.35	4.50	B-cun 2	39.10	3.50	***	6X
CUN 3	73.84	7.46	B-cun 3	58.60	5.20	***	4X
CUN 4	76.96	7.06	B-cun 4	78.20	6.90	ns	3X

* = 0.05, ** = 0.01, *** < 0.001; ^† = CUN 1B was compared to B-cun 1..

The approximate location of LI4 was found along the lateral border of the second metacarpal bonés midpoint with a mean of 33 ± 4 mm. The mean range from the distal head to LI4 was 36 ± 6 mm and from the proximal base to LI4 was 30 ± 4 mm (Fig. 2B). The approximate location of LI6 had a mean distance of 74 ± 8 mm from LI5, which was the mean equivalent of the width of all four fingers measured at the level of the proximal interphalangeal joint of the index finger (CUN 3). LI6 had a mean distance from LI11 of 156 ± 22 mm and a mean distance from LI5 of 74 ± 8 mm (Fig. 2C).

There was a positive correlation between CUN 1A and CUN 1B measurements (r(23) = 0.69, p = 0.0002, Fig. 2D). The mean measurements of CUN 1A (20 ± 2 mm) and CUN 1B (23 ± 4 mm) were statistically significant from each other (p = 0.007). Hand breadth (HB) and CUN 4 had a significant positive correlation with each other (r(23) = 0.86, p = 0.0001, Fig. 2E). The means of HB (75 ± 3 mm) and CUN 4 (77 ± 7 mm) were not statistically significant from each other (p = 0.3872). There was significant positive correlation between forearm length (FL) and the length of transverse cubital crease to the transverse carpal crease (CUN 12) (r(23) = 0.73, p = 0.0001, Fig. 2F). The means of FL (257 ± 20 mm) and CUN 12 (234 ± 21 mm) were statistically significant from each other (p = 0.0003).

When comparing f-cun measurements with b-cun calculated measurements, there were statistically significant differences of 1.5 to 3 cun (Table 4). Other investigations have reported similar findings with different body region measurements within f-cun and b-cun [1]. CUN 1A and CUN 4 were not statistically significant from the calculated b-cun (Table 4). These measurements may be a better internal correlation between f-cun and b-cun in the hand and forearm. For other body regions, more investigation needs to be done.

There were differences based on sex in the location of LI4 that were similar to other anthropometric dimensions (Table 3). Based on the distances between the distal head and proximal base of the MC II, LI4 appears to fall within a select anatomical range (Fig. 2B). There are likely several anatomical variations of structures located at this point, such as the superficial radial nerve and the dorsal venous plexus, which warrant further study [15,16].

The determination of LI6 was more challenging. LI6 was estimated to have an overall mean distance of 74 ± 8 mm from LI5 (Fig. 2C). There were differences based on sex in the location of LI6 that were similar to other anthropometric dimensions (Table 3 and Fig. 2C). In female cadavers, LI6 had a mean distance from LI5 that was smaller by about 8 to 6 mm than the overall sample. This difference may be related to the use of CUN 3 to locate LI6. There was a statistical difference in the means of 3 cun between f-cun and b-cun. This creates approximately a 1 to ½ cun measurement in error when using CUN 3 (Table 4). This finding may pose challenges in future research in locating LI6. This error may need to be taken into consideration when studying structures at this point in detail. This relationship may not be feasible with other acupoints such as Heart (HT) 4–7 since there would be an overlap between adjacent acupoints. Specific anatomical structures are in line with specific acupoints, such as dorsal rami of spinal nerves [14] or other structures deep to LI6. These anatomical relationships may offer insight into how these points relate to one another.

Body dimension differences in sex were observed and verify other studies [4]. HL, MHB, HT, CUN1B were not statistically significant between male and female cadavers (Table 3). There were also similar measurements between CUN 3 and CUN 4 (Table 3, Table 4). These results would also explain as to why there may be 1 to ½ cun error in locating LI6. There are two major factors that can contribute to these findings that may need to be taken into account when measuring LI6 for future studies:

• 1) Cadavers are embalmed, and no dynamic processes are taking place. The embalming method at LSUHSC uses a hyperperfusion technique that adds volume to the cadaver, whereas other institutions will remove blood to offset the volume being injected. The embalming process for the cadavers creates a greater volume of fluid to penetrate into the tissues for long-term study in selected gross anatomy dissection courses. The pooling of fluid regularly occurs in all parts of the soft tissue in the cadavers and is most pronounced in the extremities. This is also dependent on the cadaver’s height, weight, and BMI.

• 2) A few cadavers were observed. Most of the data collected were similar to results of other researchers who measured the same anthropometric or cun measurements in living human beings with a greater number of participants [1,4,5,8]. The results do support these measurement systems as valid methods to locate acupoints in cadavers for further investigation into the anatomical relationships of specific points [14]. The amount of error seen in this study can offer an opportunity to better visualize structures closely associated with specific acupoints. Anatomical relationships need good visualization in order to fully document the structures involved.

There were several CUN measurements that had positive correlations with other measurements (Fig. 2D–F). CUN 1A and CUN 1B were compared to see if they had the equivalent of 1 cun and could be used interchangeably in future studies. The challenge was that these two measurements rely on different landmarks. CUN 1A depends on the distance on the first interphalangeal joint, whereas CUN 1B depends on the skin folds of the middle interphalangeal joint, which may account for the larger degree of variation (Table 3). CUN 1A was more consistent between f-cun and calculated b-cun measurements, whereas CUN 1B was not (Table 4). Both of these findings could be interpreted that CUN 1A measurement may be more consistent and precise than CUN 1B in cadavers.

FL and CUN 12 were compared to see if these body measurements could act as equivalent measurements between anthropometric and cun measurements. The challenge for these two measurements was the size of the forearm. FL is limited by the length of the ulna bone and is not affected by muscle mass or fluid retention, whereas CUN 12 and the distance between LI5 to LI11 are. As different parts of forearm circumference increase, the length will increase. Individuals with the same height, weight, and bone proportions will have similar dimensions skeletally; however, muscle tone, hypertrophy, or atrophy will affect the distance in CUN 12. This may also contribute to the challenges seen in using f-cun and b-cun in locating specific acupoints in the forearm [8,9,10].

When HB and CUN 4 were compared, there seems to be some similarities between anthropometric and cun measurements (Table 2, Table 3). Statistically, they are identical, and they have similar descriptions when measuring. CUN 4 also was more consistent between f-cun and b-cun measurements in the hand and forearm (Table 4). The relationships observed here give strong support that HB and CUN 4 have common measurements that can overlap between cun and anthropometric systems.

When comparing cun and anthropometric dimensions, there is a degree of variability that seems to reflect normal anatomical variation (Table 3 and Fig. 2). This degree of variability may only be specific for the upper extremity, as seen in this study. The data presented verify the location of LI4 with a small variable range. The location of LI6 has more variability in discerning the location with f-cun and b-cun methods. This variability should be taken into account in future studies.

The author sincerely thanks those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase mankind’s overall knowledge that can then improve patient care. Therefore, these donors and their families deserve our highest gratitude [17].

Undergraduate students Lauren Bridevaux (third-year nursing student) and Dominic Neil (fourth-year respiratory therapy student) collected the anthropometric and Chinese inch data under the author’s direction and supervision. They had both previously enrolled in an anatomy dissection course using cadavers at LSUHSC prior to their involvement in this study.

Anthony Wells, Shenell Thomas, and Maggie Hales embalmed and prepared the cadavers according to the Environmental Health and Safety Department at the LSU Health Sciences Center in New Orleans and under Occupational Safety and Health Administration’s policy and guidelines.

Dawn Woods and the Louisiana Bureau of Anatomical Services provided age and demographic data on each of the cadavers in the study.

The author supervised and/or coordinated with all contributors to the project. He located LI4 and LI6 on all cadaveric specimens for this study. He compiled, analyzed, and tabulated all the data, reviewed the literature, and wrote the manuscript.

The Louisiana State University Health Sciences Center in New Orleans and the Department of Cell Biology and Anatomy provided the facility to perform measurements on the cadavers.

There is no conflicts of interest involved in the development and production of this research.