Medial Malleolus

The medial malleolus is the prominent bony projection located on the distal end of the tibia, along its medial aspect. It forms the medial portion of the ankle joint and serves as a stabilizing element for the ankle mortise, articulating with the talus and contributing to the structural integrity of the tibiotalar joint. In addition to its articulatory role, the medial malleolus acts as a pulley and attachment site for several key ligaments that control ankle motion and provide resistance to inversion injuries.

Structure

The medial malleolus is a pyramidal or quadrangular-shaped extension of the distal tibia, projecting inferiorly and medially. It is composed of dense cortical bone externally and cancellous bone internally. The surface is smooth and curved where it articulates with the talus and is rough and grooved where tendons and ligaments attach. Its size, shape, and angulation vary slightly between individuals and can influence joint mechanics and injury susceptibility.

Components

• Anterior border: Continuous with the tibial shaft, forms the anterior margin of the ankle mortise
• Posterior border: Grooved by the tendon of the tibialis posterior muscle
• Medial surface: Subcutaneous, easily palpable just above the medial side of the ankle
• Inferior articular surface: Smooth and concave, articulates with the medial surface of the talus

Location

The medial malleolus is located at the distal end of the tibia on its medial side. It lies slightly anterior and inferior to the lateral malleolus of the fibula. It can be palpated on the inner aspect of the ankle and forms the medial border of the ankle mortise — the socket into which the talus fits.

• Superior: Continuous with the tibial diaphysis
• Inferior: Articulates with the medial side of the talus
• Lateral: Faces the tibiotalar joint space
• Medial: Lies just beneath the skin and superficial fascia

Function

• Articulatory support: Forms the medial boundary of the ankle joint and contributes to joint congruency
• Stabilization: Provides resistance to valgus and eversion forces during gait and weight-bearing
• Ligament attachment: Acts as an anchoring site for the strong deltoid ligament complex

Articulations

The medial malleolus articulates with the medial surface of the talus to form part of the tibiotalar (ankle) joint. The articulation is smooth, concave, and covered with hyaline cartilage. It contributes to ankle dorsiflexion and plantarflexion by maintaining congruent movement with the talus.

Ligament Attachments

The medial malleolus is the attachment site for the deltoid ligament, a strong, fan-shaped ligament complex that stabilizes the medial aspect of the ankle. The deltoid ligament has superficial and deep layers, both originating from the medial malleolus.

Deltoid Ligament Component	Origin (Medial Malleolus)	Insertion	Function
Anterior tibiotalar ligament	Anterior aspect	Anterior medial talus	Limits plantarflexion and external rotation
Tibiocalcaneal ligament	Middle portion	Sustentaculum tali of calcaneus	Resists eversion and valgus stress
Posterior tibiotalar ligament	Posterior aspect	Posterior talus	Resists dorsiflexion and external rotation
Tibionavicular ligament	Anterior portion	Navicular tuberosity	Stabilizes anterior medial ankle

Muscle and Tendon Relations

Several tendons pass posterior to the medial malleolus, enclosed in a shared synovial sheath and held in place by the flexor retinaculum. These include:

• Tibialis posterior tendon: Passes directly behind the medial malleolus in a shallow groove
• Flexor digitorum longus tendon: Lies just lateral to the tibialis posterior tendon
• Flexor hallucis longus tendon: More posterior and lateral, although not directly adjacent to the malleolus

The arrangement of these structures is remembered with the mnemonic: Tom, Dick, And Nervous Harry — Tibialis posterior, flexor Digitorum longus, posterior tibial Artery, tibial Nerve, and flexor Hallucis longus.

Blood Supply

The blood supply to the medial malleolus is provided by branches of the posterior tibial artery and the anterior medial malleolar artery (from the anterior tibial artery). These vessels form an anastomotic network around the ankle joint to supply the periosteum, ligamentous structures, and overlying skin.

• Posterior tibial artery: Main supply to posterior and inferior aspect
• Anterior medial malleolar artery: Supplies anterior and medial regions

Nerve Supply

The medial malleolus and adjacent structures are innervated by branches of the tibial nerve and saphenous nerve.

• Tibial nerve: Provides articular and periosteal branches to the joint and ligament attachments
• Saphenous nerve: Gives cutaneous innervation to the skin over the medial malleolus and medial ankle

Ossification

The medial malleolus develops as part of the distal tibial epiphysis and ossifies through endochondral processes. There is no separate ossification center for the malleolus — it grows and fuses as part of the tibial growth plate.

• Distal tibial epiphysis appears: Around 3–6 months of age
• Fusion with diaphysis: Around 15–18 years of age

Abnormal development may result in angular deformities or joint misalignment, particularly in pediatric patients with trauma to the growth plate.

Clinical Significance

• Medial malleolus fracture: Commonly associated with ankle sprains or high-energy trauma. Often part of bimalleolar or trimalleolar fractures. May involve the deltoid ligament and joint instability.
• Posterior tibial tendon dysfunction: Can cause medial ankle pain and flattening of the medial arch; dysfunction may result in abnormal traction near the malleolus.
• Tarsal tunnel syndrome: Compression of the tibial nerve posterior to the medial malleolus, causing burning or tingling sensations in the sole of the foot.
• Open fractures: Due to the subcutaneous nature of the medial malleolus, it is frequently exposed in open ankle injuries.

Imaging

• X-ray: AP, lateral, and mortise views of the ankle visualize the medial malleolus and assess for fracture, displacement, or joint space narrowing.
• CT scan: Helpful for evaluating complex fractures, comminution, and intra-articular extension.
• MRI: Used to assess ligament attachments, marrow edema, stress injuries, or tarsal tunnel pathology.
• Ultrasound: Useful for dynamic evaluation of posterior tibial tendon and surrounding soft tissues.