GENERAL INFORMATION
The fibularis tertius, also known as the peroneus tertius, is a muscle in the lower leg’s anterior compartment. It is one of the lateral (fibular) muscles and plays a role in ankle dorsiflexion and eversion. The fibularis tertius assists in stabilising the ankle and foot during walking and other weight-bearing activities.
ORIGIN
The fibularis tertius muscle originates from two locations:
- The lower one-third of the fibula is the smaller bone of the lower leg. It specifically arises from the anterior surface of the fibula.
- The interosseous membrane is a fibrous tissue connecting the fibula and the tibia (the more significant lower leg bone).
- These origins provide the muscle with the necessary leverage for its function.
INSERTION POINT
The fibularis tertius muscle inserts onto the dorsal surface of the base of the fifth metatarsal bone, which is located in the foot. Consequently, this insertion allows the muscle to perform its actions on the foot effectively.
MAJOR ARTERIES
The fibularis tertius muscle receives blood supply from branches of the anterior tibial and peroneal arteries. These arteries provide oxygenated blood to the muscle to support its function.
NEURAL INNERVATION
The fibularis tertius muscle is innervated by the deep fibular nerve (also known as the deep peroneal nerve). This nerve arises from the common fibular nerve. It provides both motor innervation for muscle contraction and sensory innervation for transmitting sensations from the skin of the lower leg and dorsum of the foot.
TRIGGER POINT
Trigger points can develop in it, causing localised pain and tenderness. These trigger points may be associated with muscle overuse, strain or postural imbalances. Therefore, addressing these trigger points is essential for managing pain and ensuring proper muscle function.
CONCENTRIC FUNCTION
The concentric function of the fibularis tertius is to actively contract and generate force during ankle dorsiflexion and eversion. This action involves lifting the front of the foot and turning it outward, which is crucial for walking and running.
ECCENTRIC FUNCTION
During controlled foot lowering and inversion, the fibularis tertius muscle functions eccentrically to resist the force of gravity and control the movement. As a result, this eccentric function helps in maintaining balance and stability.
ISOMETRIC FUNCTION
It can contract isometrically to stabilise the ankle and foot during weight-bearing activities, maintaining alignment and preventing excessive movement. Consequently, this isometric function is essential for postural control and stability.
RELATED MUSCLE-SCIENTIFIC NAMES
The Fibularis Tertius muscle is also known as:
- Musculus Fibularis Tertius
ANTAGONIST MUSCLES
- Gastrocnemius: Located in the posterior compartment of the lower leg, responsible for plantar flexion (pointing the foot downward), opposing the dorsiflexion action of the Fibularis Tertius.
COMMON INJURIES
- Tendinitis or Tendon Rupture: Inflammation or tearing of the tendon, often due to overuse or sudden injury, leading to pain and impaired movement.
- Muscle Strains or Tears: Overstretching or excessive force can cause muscle fibres to tear, resulting in pain and reduced function.
- Ankle Sprains: Ligament injuries around the ankle joint can affect the Fibularis Tertius, causing pain and instability.
EXERCISES
- Ankle Dorsiflexion Exercises Using Resistance Bands: Secure a resistance band around the forefoot and pull the toes towards the shin against the band’s resistance. Strengthens the Fibularis Tertius and improves dorsiflexion strength.
- Toe Raises and Toe Curls: Stand with feet flat, raise the toes off the ground, hold for a moment, then curl the toes under. Engages and strengthens the lower leg muscles, including the Fibularis Tertius.
- Balance Exercises on Unstable Surfaces: Stand on a balance board or cushion to challenge stability and engage the lower leg muscles. Enhances the strength and coordination of the Fibularis Tertius and other stabilising muscles.
- Lateral leg Raises: Lie on one side, lift the top leg upward, hold for a moment, then lower it back down. Strengthens the lateral muscles of the lower leg, including the Fibularis Tertius.
- Single-Leg Calf Raises: Stand on one leg and raise the heel off the ground, hold, then lower back down. Engages the calf muscles and the Fibularis Tertius for improved balance and strength.
STRETCHES
- Calf Stretches: Stand facing a wall, place one foot back with the heel on the ground and lean forward into the wall. Stretches the calf and lower leg muscles, including the Fibularis Tertius.
- Ankle Dorsiflexion Stretch: Sit with legs extended, loop a towel around the football and gently pull the toes towards the shin. Stretches the Tibialis Anterior and Fibularis Tertius, improving ankle mobility.
- Soleus Stretch: Stand with one foot back, slightly bent and push the heel into the ground. Targets the deeper calf muscles, including the soleus and the lower leg.
- Heel Drop Stretch: Stand on a step with the heels hanging off and slowly lower the heels below the step level. Stretches the calf muscles and lower leg muscles, including the Fibularis Tertius.
- Seated Forward Fold: Sit with legs extended, reach towards the toes and hold. Stretches the hamstrings and lower leg muscles, improving overall flexibility.