Sanyinjiao (SP-6) - Three Yin Crossing

 SP-6 is widely known as a point where the three yin channels of the leg cross. Therefore it is a place where the three leg yin channels (Spleen, Liver, and Kidney) can be simultaneously influenced. Most commonly, this is used to influence these channels to influence the production of Blood, since, according to Traditional Chinese Medicine, all three of these channels/organs contribute to Blood production.

Fig 2: The deep posterior

compartment, including the

tibialis posterior. The

soleus has been removed to

reveal the deeper structures

Fig. 1: Soleus muscle.
The more superficial
gastrocnemius muscle
has been removed.

There is an intriguing anatomical consideration of SP-6 which I have been interested in recently, and was able to confirm this past week while preparing a cadaver specimen for the Sports Medicine Acupuncture Certification Lower Extremity Module. The Anatomy, Palpation and Cadaver Lab portion of the lower extremity module was Thursday and Friday of this past week (9/10/15 and 9/11/15) and, since dissection was a part of this class, I was able to closely observe the region of SP-6 and confirm my suspicion, which is discussed below.

When teaching the Spleen sinew channel, I include the tibialis posterior muscle as
part of a series of myofascially linked structures connecting the medial arch to the knee and thigh. Tibialis posterior is the middle muscle of the deep posterior compartment. The placement of the muscles behind the tibia from medial to lateral is as follows: flexor digitorum longus - tibialis posterior - flexor hallucis longus. Therefore, if you were to insinuate your fingers under the tibia in the region of SP-7 or SP-8, you would encounter the flexor digitorum. If you were able to continue, you would contact the tibialis posterior and then the flexor hallucis longus. Inferior to this, the tibialis posterior then crosses under (anterior to) the flexor digitorum longus and, by the time it passes behind the medial malleolus, it is the most anterior of the deep posterior compartment muscles (recall the mnemonic 'Tom, Dick and Harry' to remember the order of the tendons at the medial malleolus).

Fig 3: Deep posterior compartment
tendons as they pass posterior to the
medial malleolus. These are (in
order) tib posterior, flexor digitorum
longus, flexor hallucis longus

SP-6 is the region at which the tibialis posterior emerges from under the flexor digitorum longus to become the most medial muscle. Flexor digitorum longus is part of the Liver sinew channels. In addition, this region is very close to the soleus muscle at this level. I include the soleus as part of the Kidney sinew channel.

Therefore, SP-6 is at an anatomical location where there is a literal crossing of the three yin sinew channels. This accounts for the usefulness of SP-6 as a distal point for knee pain. This is especially the case when the knee pain has a component of disruption of the musculature of the Spleen sinew channel and can include conditions such as chondromalacia patella, patellofemoral syndrome, and pes anserine tendinopathy.

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