The fibularis longus, also referred to as the peroneus longus, is a long muscle located along the outer side of the lower leg. It is fundamental for the mechanics of the foot and ankle, contributing significantly to both movement and stability. The muscle acts as a dynamic rope, initiating certain foot movements while also providing support during standing and walking.
Where is the Fibularis Longus Located
The fibularis longus originates high on the leg, attaching to the head and the upper two-thirds of the lateral surface of the fibula bone. It is situated in the lateral compartment of the leg, alongside the fibularis brevis, and is the more superficial of the two muscles. The muscle belly extends downward, transitioning into a long, strong tendon.
The tendon wraps around the bony prominence on the outside of the ankle, known as the lateral malleolus. It continues its path by crossing underneath the sole of the foot at an angle. It then attaches to the medial cuneiform and the base of the first metatarsal on the opposite, inner side of the foot. The muscle is innervated by the superficial fibular nerve, which controls its contractions.
Primary Actions of the Fibularis Longus
The muscle’s unique anatomical path enables it to perform two primary movements at the ankle joint. The most powerful action is eversion, which involves tilting the sole of the foot outward, away from the body’s midline. This movement is performed in conjunction with the other fibularis muscles.
The second primary action is plantar flexion, the movement of pointing the toes downward, similar to pressing a gas pedal. While the main calf muscles are the strongest plantar flexors, the fibularis longus assists in this action, making it a synergist. It also helps to stabilize the foot and leg, especially when standing on one leg.
Essential Role in Foot Stability
The fibularis longus plays a fundamental role in maintaining the structure and balance of the foot under body weight. Its tendon crosses the sole of the foot obliquely, creating a dynamic sling that supports the foot’s arches. This tension is applied to the transverse arch and, to a lesser extent, the medial longitudinal arch.
This muscle balances the foot against forces exerted by other muscles that tend to roll the foot inward, or invert it. By maintaining tension across the sole, the fibularis longus stabilizes the foot during the stance phase of walking and running. This counter-pull prevents excessive supination or inversion, a common mechanism for ankle sprains. The muscle’s ability to lock the first metatarsal ray provides stability to the medial arch, ensuring the foot can function as a rigid lever for propulsion.
Common Injuries and Related Symptoms
The fibularis longus and its tendon are susceptible to injuries, largely due to overuse or sudden trauma. The most frequent problem is tendinopathy, a degenerative condition sometimes involving inflammation or small tears. This often results from repetitive strain, such as in runners, or from activities requiring frequent side-to-side movements.
Patients experience pain along the outer ankle, just behind or below the lateral malleolus, or on the outside of the foot. Swelling and tenderness are common along the course of the tendon. The pain is aggravated by weight-bearing activities, especially when walking or running on uneven surfaces. Acute tears can also occur, frequently associated with severe ankle inversion sprains.