Exploring the Applicable Parts of Thumb and Middle Finger Measurements Based on Different Methods of Locating Acupuncture Points

Abstract Background To explore the difference between thumb and middle finger measurements and proportional bone measurements and identify the applicable parts of thumb and middle finger measurements in each part of the body. Methods A total of 394 healthy adults were enrolled. A high-precision electronic ruler was used to measure the lengths of their thumb and middle finger cun and the lengths of their bone proportional cun of the head–face, limbs, and trunk. The lengths of bone proportional cun were converted into a “1 cun ”, which were compared with the lengths of the thumb and middle finger cun . Results The thumb and middle finger cun are both commonly said to be “1 cun ” in length, but actual measurements revealed that the middle finger cun is significantly longer than that of the thumb cun ( P < 0.001). The thumb cun is generally significantly shorter than that of the bone proportional cun ( q < 0.001). However, there was no significant difference in the length of the thumb cun compared with the length of the bone proportional cun after conversion to “1 cun ” at the cubital crease (olecranon) to the most distal palmar (dorsal) wrist crease, upper edge of the pubic symphysis to the base of the patella, and greater trochanter of the femur to the popliteal crease ( q > 0.05). The middle finger cun is generally significantly longer than the bone proportional cun ( q < 0. 05 or q < 0.001). However, there was no significant difference in the length of the middle finger cun compared with the length of the bone proportional cun after conversion to “1 cun ” at the suprasternal fossa ( Tiantu , CV22) to the xiphisternal junction, underneath the medial tibial condyle ( Yinlingquan , SP9) to the prominence of the medial malleolus, gluteal fold to the popliteal crease, popliteal crease (apex of the patella) to the prominence of the lateral malleolus, and prominence of the medial malleolus to the plantar ( q > 0.05). Conclusion The middle finger cun is significantly longer than that of the thumb cun . The compatibility of finger cun measurements with the proportional bone standard varies by anatomical region. These findings provide an anthropometric basis for optimizing the selection of acupoint location methods in teaching and standardization. For educational purposes and in standard-body-type individuals, our data suggest that the thumb measurement might be prioritized in regions such as the head, face, and forearm, while the middle finger measurement may be more appropriate for areas such as the upper arm and lower leg, thereby balancing operational convenience with acupoint localization accuracy. Graphical abstract