Thursday, April 20, 2017

The Fascial Slings of the Foot and the Balance of the Arches, Part 2

Part 1 of this post introduced the fascial sling which connects at the plantar portion of the medial arch. It includes the tibialis anterior and peroneus longus muscles. The tibialis posterior can also be included in this sling, and the last post looked at how the tibialis anterior (part of the Stomach sinew channel) and the tibialis posterior (part of the Spleen sinew channel) can function synergistically to lift the medial arch. It was discussed that the healthy T&T function of the Spleen-Stomach can help nourish these muscles and that a drop of the medial arch can be seen as part of the Spleen's holding or lifting function. See the previous post for this discussion.

This post will look at the main part of this fascial sling, the tibialis anterior - peroneus longus. This convergence of the Stomach and Urinary bladder sinew channels has a more agonist-antagonist relationship, and working to balance these muscles/channels is key to proper balance in the arches of the foot.

Fig. 1
The peroneus longus (aka the fibularis longus) attaches from the head and proximal portion of the fibula. It traverses the lateral portion of the fibula, passes posterior to the lateral malleolus, travels just superior to UB-62, and crosses under the cuboid bone in the peroneal canal which is created superiorly by the cuboid sulcus and inferiorly by the long plantar ligament. It reaches the medial cuneiform and base of the 1st metatarsal which is its distal attachment. This is the same attachment site as the tibialis anterior, and they connect to one another through the joint capsules of these bones. When it contracts, the peroneus longus creates plantar flexion at the ankle, which pulls on the lateral arch and everts the foot. When it is overactive, it can contribute to foot overpronation by pulling up on the lateral arch and dropping the medial arch.

Fig. 2: Note the lateral branch of the UB
sinew channel which travels behind the lateral
malleolus. Image is from Deadman's
A Manual of Acupuncture.
The peroneus longus is part of the lateral branch of the Urinary Bladder sinew channel (Fig. 2). This muscle has a very strong fascial connection into the biceps femoris (lateral hamstring). For more on this connection, see this past post. This muscle acts as an antagonist to the tibialis anterior muscle (part of the ST sinew channel), which performs dorsiflexion at the ankle and inverts the foot at the subtalar joint.

Fig. 3
Fig. 4
Many agonist-antagonist muscle imbalances are seen between the Stomach (Earth) and Urinary Bladder (Water) sinew channels. Examples include the quadriceps (ST) - hamstrings (UB) and rectus abdominis (ST) - erector spinae (UB). The relationship between the tibialis anterior (ST) and the peroneus longus (UB) is another example.

When the peroneus longus is locked-short and the tibialis anterior is locked long, the foot will be pulled into eversion (Fig.4). Alternately, when the tibialis anterior is locked-short and the peroneus longus is locked-long, the foot will be pulled into inversion.

Treatment can include needling the most reactive tibialis anterior motor point; ST-36 is often the most reactive, but the extra point lanweixue M-LE-13 is also a motor point. And the peroneus longus MP (approximately 1 cun inferior to the fibular head) can also be needled.

There are some more specific advanced techniques that Matt Callison and I will demonstrate at the Pacific Symposium this coming Fall 2017, involving an acupuncture fascial release that helps pull down the lifted UB sinew channel for foot overpronation. This is a bit tricky to discuss in a blog post, but stay tuned for more information in the future.

The next and final post in this series will follow the sinew channels up to the hip and explore how pelvic imbalances can influence foot overpronation.