Sunday, January 7, 2018

Sinew Channels and the Architecture of the Carpal Tunnel

Fig. 1: Cross section of carpal tunnel
The carpal tunnel is created by the concave shape of the volar (palmar side) surface of the carpal bone which makes up the floor of the carpal tunnel, and the thick, fibrous flexor retinaculum which makes up the roof (Fig.1). This structure is like a bow, with the carpal bones forming the body of the bow and the retinaculum forming the bowstring. If the bow becomes too flat and looses its concavity, the tunnel becomes narrowed and the neurovascular structures passing through this tunnel can become entrapped (particularly the median nerve).

Proper shape of this bow-like structure is influenced by the Pericardium and Sanjiao sinew channels. Both of these sinew channels include the finger and thumb flexors and extensors (P – flexors, SJ – extensors) and the forearm pronators and supinators (P – pronators, SJ – supinators). How these muscles interact affect the relationship of the radius and ulna which, in turn, affects the shape of the tunnel.

Fig. 2: Pronator quadratus on the
volar side of forearm.
Imagine that you are typing with the wrist extended and the forearm pronated. The extension of the wrist tends to flatten the carpal tunnel and rolls the ulna and radius away from the volar side of the arm. The pronator quadratus muscle, located at the distal portion of the forearm, is uniquely positioned to pull the radius and ulna in the opposite direction, rolling them towards the volar side and maintaining the integrity of the tunnel (Fig. 2). If this muscle becomes inhibited, it fails to maintain the proper relationship between the two bones, and the carpal tunnel loses its depth leading to a compression of the median nerve and a greater possibility of paresthesia in the median nerve distribution of the palm and fingers.

Many acupuncturists use a threading technique through the flexor retinaculum at P-7. This technique is effective in creating space in the carpal tunnel. An additional technique, developed by Matt Callison and taught in the Sports Medicine Acupuncture Certification program, addresses the inhibited pronator quadratus muscle. This is done if it is determined that the pronator quadratus is indeed inhibited. The needling technique for the motor point of this muscle, which will help to wake it back up and bring it back into the neurological loop, is a bit tricky as the motor point lies directly deep to the median nerve at P-6. So, one can't simply drive the needle deep into P-6 to reach it without risking damage to the median nerve. This technique is best discussed and demonstrated in a class setting. It is a very effective technique and can improve clinical results because of its strong action on the pronator quadratus, so that it can have a profound effect on the relationship of the radius and ulna, and can add integrity to the carpal tunnel.

Fig. 3: An old-fashion pup tents which is a tensegrity structure. The
tension from the guy wires give the structure integrity, much like the
shape of the carpal tunnel is given integrity by the balanced pull of
the pericardium and sanjiao sinew channels.
An analogy to consider for proper balance and integrity of the carpal tunnels is an old-fashioned pup tent. These tents require a balanced tension in the guy wires to stabilize the shape of the tent (Fig. 3). This balanced tension creates an open space inside the tent. If the guy wire tension is unbalanced, one side is too short and tight and the other too slack, the tent will lose its shape and sag. This is very much the same with the open shape of the carpal tunnel, and it is the muscles of the pericardium and san jiao sinew channels that create a balancing pull to maintain the integrity of the tunnel. Imbalance between these channels will lead to a less than optimal shape and increase the chance of compression of the structures traveling through the tunnel. So it is important to look for imbalances between these two channels and treat accordingly.

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  1. My uneducated guess is that you'd have to thread from Sj5 to get the Pronator Quadratus muscle without the median nerve.

  2. You are correct, but this would probably be a bit uncomfortable and you risk a needle bend or even break if the patient moves too much. There are a couple of ways you can get to it from the volar side of the arm at or near P6, but it is a bit tricky to discuss in a blog safetly.