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Peroneus Tertius (PT) muscle is peculiar to man, and man is the only member among the primates in whom this muscle occurs. It often appears to be a part of extensor digitorum longus, and might be described as its “fifth tendon”. The muscle is variable in its development and attachment. Because of functional demands of bipedal gait and plantigrade foot, part of extensor digitorum brevis (EDB) has migrated upwards into the leg from the dorsum of foot. PT is a muscle that evolution is rendering more important. In a total of 110 cadavers, extensor compartment of leg and dorsum of foot were dissected in both the lower limbs and extensor digitorum longus (EDL), and PT muscles were dissected and displayed.
The peroneus tertius (also known as fibularis Tertius) is a muscle of the human body located in the lower limb. The muscle arises from the lower third of the anterior surface of the fibula (anterior compartment of the lower leg); from the lower part of the interosseous membrane; and from an intermuscular septum between it and the peroneus brevis muscle. The septum is sometimes called the intermuscular septum of Otto.
The tendon, after passing under the superior extensor retinaculum of foot and inferior extensor retinaculum of the foot in the same canal as the extensor digitorum longus, is inserted into the dorsal surface of the base of the metatarsal bone of the fifth digit.
Anatomy of Peroneus Tertius
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The peroneus Tertius is the third and final muscle of the lateral peroneus or fibular muscles
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Origin: The peroneus Tertius originates from the middle fibular shaft
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Insertion: The dorsal surface of the fifth metatarsal
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Action: Dorsiflex, evert, and abduct the foot
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Blood Supply: The peroneus tertius primarily receives its blood supply from the anterior tibial artery
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Innervation: Peroneus tertius innervation comes from the deep peroneal nerve, an innervation different than its similarly named peroneal counterparts
Nerve Supply of Peroneus Tertius
- Fibularis tertius receives innervation via the deep fibular nerve, a branch of the sciatic nerve. It originates from the L5 and S1 spinal nerves.
Blood Supply of Peroneus Tertius
Fibularis tertius receives arterial blood from several sources
- Anterior tibial artery – via the anterior lateral malleolar artery
- Dorsalis pedis artery – and its branches, such as a lateral tarsal artery, arcuate artery, metatarsal arteries, fourth dorsal metatarsal artery, and digital arteries
- Posterior tibial artery – via the lateral plantar artery
Function of Peroneus Tertius
Due to its poor mechanical leverage, fibularis tertius can produce only two weak movements:
- Foot dorsiflexion – around the talocrural (ankle) joint, with the help of extensor digitorum longus and tibialis anterior muscles.
- Foot eversion – at the subtalar joint with the aid of fibularis longus and fibularis brevis muscles.
Through these actions, fibularis tertius has a role in the gait cycle, acting with another foot dorsiflexion during the swing phase to clear the foot and toes off the ground. In addition, it has supporting functions for the ankle joint, preventing excessive inversion of the foot during physical activities. However, it is difficult to assess the true importance of fibularis tertius because its actions can be completed efficiently by other, more powerful muscles. In fact, fibularis Tertius is absent in many individuals who don’t accuse any particular movement impairment.
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