Peroneus Longus Muscle

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The peroneus longus muscle, whose name means "long muscle of the fibula" is a major muscle of the lower leg that plantar flexes and everts the foot at the ankle. Also known as the fibularis longus, it is the longest muscle that attaches to the fibula and is used specifically when balancing one's weight on one foot.

The peroneus longus muscle has its origin along the lateral edge of the head and proximal shaft of the fibula, just below the styloid process of the fibula. From its origin, it descends along the lateral edge of the leg as a thin strap of muscle in the lateral compartment of the leg. About halfway between the knee and ankle, it tapers to a point and begins to form a long tendon. The tendon of the peroneus longus passes through the ankle posterior to the lateral malleolus and wraps around the sole of the foot. It forms its insertion at the first metatarsal and first (medial) cuneiform bones on the medial edge of the foot.

The peroneus longus performs two major functions in the leg by plantar flexing and everting the foot. Working as a plantar flexor, the peroneus longus assists the much larger gastrocnemius and soleus muscles in pointing the toes, allowing the body to stand on its tiptoes. The peroneus longus may also evert the foot by pulling the sole laterally toward the lateral malleolus. Eversion of the foot is an important part of standing on one foot, centering the body's weight over the planted foot. The contraction of the peroneus longus muscle also helps to support the transverse arch of the foot by holding the tarsal bones and metatarsal bones in the correct anatomical position.

The word peroneus comes from the Greek word for "clasp," while the word fibula is the Latin translation of the same word. These words refer to how the fibula attaches on both ends to the much thicker tibia like a thin clasp pin connects to the back of a button or brooch.