What muscle controls the outer edge of the foot?

The Peroneus Brevis Muscle Controls the Outer Edge of the Foot

The peroneus brevis muscle is the primary muscle that controls the outer edge of the foot, providing more effective eversion than the peroneus longus muscle. 1

Anatomy of the Lateral Ankle Muscles

• The peroneus brevis and peroneus longus muscles are located in the lateral compartment of the lower leg and are primarily responsible for eversion of the foot (turning the sole outward) 2, 1
• The peroneus brevis has been demonstrated to be a more effective evertor than the peroneus longus, producing greater calcaneal valgus and external rotation of the navicular when the same force is applied to both tendons 1
• The peroneus brevis tendon runs behind the lateral malleolus and attaches to the base of the fifth metatarsal bone on the outer edge of the foot 2
• The peroneus longus has a longer course, passing under the foot to insert on the medial plantar aspect of the foot 3

Functional Significance

• The peroneus brevis provides greater eversion moment at the subtalar joint (0.9 degrees more calcaneus valgus) compared to the peroneus longus when subjected to the same load 1
• At the talonavicular joint, the peroneus brevis produces 2.1 degrees more external rotation of the navicular than the peroneus longus 1
• In patients with lateral ankle sprains, studies have shown that peroneus brevis may undergo hypertrophy and increased activity to compensate for decreased peroneus longus activity 4

Clinical Implications

• Strengthening of the peroneus muscles, particularly the peroneus brevis, is crucial in rehabilitation of lateral ankle instability 5
• In cases of lateral ankle sprain, the peroneus brevis often becomes overactive while the peroneus longus shows decreased activity 4
• For patients with chronic ankle instability, both peroneus longus and brevis training improve outcomes, but peroneus longus training shows greater improvement in eversion strength and balance 5
• When surgeons need to sacrifice one of the peroneal tendons, preserving the peroneus brevis is generally preferred for maintaining effective eversion function 1

Additional Considerations

• A third peroneal muscle, the peroneus tertius, is present in humans but is variable in its development and attachment, being absent in approximately 10.5% of limbs 6
• The dorsalis pedis pulse can be palpated on the dorsum of the foot just lateral to the extensor tendon of the big toe, which is an important anatomical landmark near the lateral aspect of the foot 2
• Proper foot biomechanics rely on the balance between the invertor and evertor muscles of the ankle, with the peroneus brevis playing a crucial role in preventing excessive inversion 2

Understanding the dominant role of the peroneus brevis in controlling the outer edge of the foot is important for clinical assessment, rehabilitation protocols, and surgical decision-making in cases of lateral ankle pathology.