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The Peroneus Tertius Muscle
Let’s talk about peroneus tertius, which is also called fibularis tertius. This is a muscle that can be left out of anatomy teachings. It the smallest of the three peroneal muscles. Anatomical information for peroneus tertius is as follows: O: Lower 1/3 of the anterior fibula and the anterior intermuscular septum between extensor digitorum longus and tibialis anterior I: Dorsal surface of the base of the fifth metatarsal A: Dorsiflexion and eversion (pronation) of the foot and ankle Peroneus tertius is not the primary component in any ankle or foot dysfunction, nor is it a large muscle that we spend much of our time as massage therapists touching. So, why am I fascinated by peroneus tertius? Because it is the only muscle working at the ankle and foot equally doing both dorsiflexion and eversion. Extensor digitorum longus does dorsiflexion and can mildly evert, but its main actions are dorsiflexion of the ankle and extension of digits 2-5. Tibialis anterior does dorsiflexion of the ankle, but it contracts during inversion (supination), not eversion. Peroneus longus and peroneus brevis do eversion, but they do not contract during dorsiflexion, they stretch because both of these muscles do plantar flexion. Peroneus tertius is a tiny muscle. Yet if you have client who is overpronated (i.e. the angle of the ankle is shortened on the lateral aspect, client may or may not be flat footed but the arch is lessened) and has a job where they stand a good portion of the day, it is peroneus tertius that is being effected most directly. Even a client with overpronation who sits much of the day with their feet on the floor has the foot in dorsiflexion and eversion for long periods of time. Chronic tension in peroneus tertius can be a component in anterior ankle pain and popping. It also plays a role in maintaining the misalignment of the talocrural joint, which causes weakness in the ankle that may lead to chronic ankle instability. Instability in the ankles puts more pressure on the knees, hips, and lower back. When working with the foot and ankle make sure and include peroneus tertius! We will be teaching direct releases for peroneus tertius, as well as the rest of the lower leg and foot, in our SMRT: Lower Leg & Foot class coming up in Tucson, AZ on February 28 and March 1, 2015 and in Sandy Springs, GA on March 14-15, 2015. 10% early registration discount ends one month before class date. For more information or to register for this 12 CE, NCBTMB approved course please go to https://efullcircle.com/spontaneous-muscle-release-technique-lower-leg-foot/
