Fibularis tertius

Fibularis tertius (Tendon) – What Is It?

The fibula is the bone that connects your foot to your shinbone. The fibula consists of three bones: the tibia, metatarsal and fibula. The fibula attaches to the top of your shinbone and it helps you balance when walking or running. When you walk, you use all three bones together to keep from falling over.

When you run, the fibula helps support your weight and it protects your knee joint. When you are standing still, the fibula is not used at all. However, when you are moving around, the fibula is activated and it helps stabilize your body so that you do not fall down.

What Are Its Functions?

The fibularis tertius muscle originates from the lateral aspect of the tibia (shin bone). It extends along the length of the fibula and inserts into the medial aspect of your shinbone. The fibularis tertius muscle is attached to several ligaments and tendons that attach to other muscles such as those in your calf, thigh, buttocks, lower back and shoulders.

The muscle itself is surrounded by a dense tissue called the periosteum. The superficial head fibers are surrounded by a sheath of fascia that splits into two terminal bands. It is the most superficial (closest to the skin) muscle in the lower leg.

It is an extremely thin and narrow muscle.

How Does It Move The Foot?

The fibularis tertius muscle is not directly involved in moving the foot, but it is involved in keeping balance while you walk or run. You use all three bones together to keep yourself from falling over, especially when you suddenly turn around quickly.

The tibia and fibula are firmly connected at both the knee and the ankle. The fibularis muscles (brevis and tertius) work together with other muscles to move your lower leg.

The muscles of the leg are responsible for moving the lower leg when you:

run or walk quickly,

turn your foot or ankle, or

move your toes up and down.

All muscles are attached to bones by tendons. Certain muscles work together to move a bone one way, and other muscles move the bone in the opposite direction. The muscles that move your toes up and down are called the flexors and extensors.

The muscles that turn your foot and ankle are called the invertors and evertors. For example, the muscles that keep your foot in contact with the ground when you walk or run are the evertors. The muscles that lift your foot off the ground during the swing phase are the extensors.

How Does It Relate To Other Muscles?

The tendons of the peroneus longus and brevis muscles pass behind and run parallel to the fibularis tertius muscles, but they do not intertwine or have any connections to them. The tendons of the tibialis posterior, flexor digitorum longus and fibularis longus muscles all pass in front of the fibularis tertius muscles. The extensor digitorum longus tendon runs in front of the fibularis tertius muscles, but there is no connection between them.

In particular, the peroneus longus and brevis muscles run behind the fibularis tertius muscles and help to keep your foot in contact with the ground when you walk or run. They also help keep your foot from turning too far to the inside or outside.

The extensor digitorum longus muscle helps extend your toes. It runs in front of the fibularis tertius muscle.

Sources & references used in this article:

Fibularis tertius: revisiting the anatomy by K Rourke, H Dafydd, IG Parkin – Clinical Anatomy, 2007 – Wiley Online Library

Fifth metatarsal morphology does not predict presence or absence of fibularis tertius muscle in hominids by DJ Eliot, WL Jungers – Journal of human evolution, 2000 – Elsevier

Clinical evaluation of fibularis tertius muscle prevalence by D Ramirez, C Gajardo, P Caballero, D Zavando… – Int J Morphol, 2010 –

The fibularis (Peroneus) tertius muscle in humans: a meta-analysis of anatomical studies with clinical and evolutionary implications by K Yammine, M Erić – BioMed research international, 2017 –