Ankle and Tibiofibular Joints

Ankle Joint

The ankle joint, also called the talocrural joint, is a strong weight-bearing joint located between the lower ends of the tibia and fibula and the talus bone of the foot. It supports body weight and allows movements of the foot during standing and walking.

Type

The ankle joint is a hinge-type synovial joint. It is a uniaxial joint, allowing movement mainly in one plane, namely dorsiflexion and plantar flexion.

Articular Surfaces

The ankle joint is a compound joint formed by the articulation of the distal ends of the tibia and fibula with the superior surface of the talus.

Proximal Articular Surface

The proximal articular surface forms a socket known as the ankle mortise or tibiofibular mortise. This socket is formed by the lower end of the tibia, the medial malleolus, the lateral malleolus, and the inferior transverse tibiofibular ligament. Together, these structures hold the talus firmly in position.

Distal Articular Surface

The distal articular surface is formed by the superior, medial, and lateral articular surfaces of the talus. The superior pulley-shaped surface of the talus articulates with the lower end of the tibia. The comma-shaped facet on the medial side of the talus articulates with the lateral surface of the medial malleolus. The triangular facet on the lateral side of the talus articulates with the medial surface of the lateral malleolus. These articulations provide stability while allowing smooth movements at the ankle joint.

Stability of Ankle Joint

• The upper surface of the talus is wider in the front and narrower at the back. During dorsiflexion (when the foot is lifted upward), the wider front part of the talus moves backward into the tibiofibular mortise. This wider part fits tightly between the tibia and fibula, making the ankle joint more stable.
• During plantar flexion (when the foot points downward), the narrower back part of the talus moves forward into the mortise. Since this narrower part does not fit as tightly, the ankle joint becomes less stable and is more prone to injury.

Factors Maintaining Stability of Ankle Joint

The stability of the ankle joint is maintained by the following factors:

1. The articular surfaces fit closely together and interlock with each other.
2. Strong medial (deltoid) and lateral collateral ligaments support the joint.
3. The inferior transverse tibiofibular ligament strengthens the ankle mortise.
4. The tendons crossing the ankle joint, held in place by the flexor and extensor retinacula, provide additional support.
5. The downward projection of the medial and lateral malleoli helps hold the talus securely within the ankle joint.

Ligaments

The ankle joint is supported by four main ligaments:

1. Fibrous capsule
2. Deltoid (medial collateral) ligament
3. Lateral collateral ligament
4. Inferior transverse tibiofibular ligament

Fibrous Capsule

• The fibrous capsule completely surrounds the ankle joint. It is thin and weak on the front (anterior) and back (posterior) of the joint. It is attached to the margins of the articular surfaces of the tibia, medial malleolus, lateral malleolus, and talus.
• The inner surface of the capsule is lined by the synovial membrane. A small upward extension of the synovial membrane projects into the distal tibiofibular joint.

Capsular attachments:

• The ankle joint capsule is attached to the margins of the articular surfaces, except:
  • Posterosuperiorly, where it is attached to the inferior transverse tibiofibular ligament.
  • Anteroinferiorly, where it extends onto the neck of the talus. 

Deltoid (Medial Collateral) Ligament

• The deltoid ligament is a strong, triangular ligament that strengthens the medial side of the ankle. It has two parts: a superficial part and a deep part. Both parts arise from the apex and margins of the medial malleolus.
• Superficial part: The anterior tibionavicular ligament passes to the navicular tuberosity and the medial margin of the spring ligament. The tibiocalcaneal ligament attaches to the tubercle on the lateral surface of the calcaneus. The posterior tibiotalar ligament attaches to the medial tubercle and adjacent medial surface of the talus.
• Deep part: The anterior tibiotalar ligament extends to the anterior part of the medial surface of the talus.

Lateral Collateral Ligament

• The lateral collateral ligament is a strong ligament complex that supports the lateral side of the ankle.
• It consists of three ligaments:
  • Anterior talofibular ligament
  • Posterior talofibular ligament
  • Calcaneofibular ligament
• Anterior talofibular ligament (ATFL): It is the weakest of the three lateral ligaments. It extends from the anterior margin of the lateral malleolus to the neck of the talus.
• Posterior talofibular ligament (PTFL): It is the strongest lateral ligament.  It extends from the lower part of the malleolar fossa of the fibula to the lateral tubercle of the talus.
• Calcaneofibular ligament (CFL): It is a long, rounded ligament. It extends from the apex of the lateral malleolus to the tubercle on the lateral surface of the calcaneus.

Inferior Transverse Tibiofibular Ligament

• The inferior transverse tibiofibular ligament is a strong, thick band located at the back of the ankle. It extends from the upper part of the malleolar fossa of the fibula to the posterior border of the articular surface of the tibia. It strengthens the ankle mortise and helps maintain the stability of the ankle joint.

Relations of Ankle Joint

Anterior Relations

From medial to lateral, the structures lying in front of the ankle joint are:

1. Tibialis anterior tendon
2. Extensor hallucis longus tendon
3. Anterior tibial artery
4. Deep peroneal (fibular) nerve
5. Extensor digitorum longus tendon
6. Peroneus (fibularis) tertius tendon

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Posterior Relations

From medial to lateral, the structures behind the ankle joint are:

• Tibialis posterior tendon
• Flexor digitorum longus tendon
• Posterior tibial artery
• Tibial nerve
• Flexor hallucis longus tendon

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Posterolateral Relations

• The peroneus (fibularis) longus and peroneus (fibularis) brevis tendons pass behind the lateral malleolus and cross the posterolateral aspect of the ankle joint.

Blood Supply and Innervation

Blood Supply

The ankle joint receives its blood supply from the malleolar branches of the:

• Anterior tibial artery
• Posterior tibial artery
• Peroneal (fibular) artery

Never Supply

The ankle joint is supplied by branches of the:

• Deep peroneal (fibular) nerve
• Tibial nerve

Movements

The ankle joint mainly allows two movements:

Dorsiflexion

• In dorsiflexion, the forefoot is lifted upward toward the leg. As a result, the angle between the front of the leg and the dorsum (top) of the foot decreases.
• The normal range of dorsiflexion is about 20°.
• Dorsiflexion is the closed-packed position of the ankle joint. In this position, the articular surfaces fit together most closely, and the ligaments become tight. This provides maximum stability and helps prevent dislocation.

Plantar Flexion

• In plantar flexion, the forefoot points downward. As a result, the angle between the front of the leg and the dorsum of the foot increases.
• The normal range of plantar flexion is about 45°.
• Plantar flexion is the loose-packed position of the ankle joint. In this position, the narrow posterior part of the trochlea of the talus fits less securely into the tibiofibular mortise. As a result, the joint becomes less stable and is more prone to dislocation.

Note: The muscles responsible for dorsiflexion and plantar flexion are discussed separately in the muscle tables or relevant chapters.

Table 15.1: Movements of ankle joint

Movement	Action	Main Muscle	Accessory Muscles
Dorsiflexion	Raises the forefoot	Tibialis anterior	Extensor digitorum longus, Extensor hallucis longus
Plantar flexion	Depresses the forefoot	Gastrocnemius	Plantaris, Tibialis posterior, Flexor hallucis longus, Flexor digitorum longus

Tibiofibular Joints

The tibia and fibula are connected at three joints:

1. Superior tibiofibular joint
2. Middle tibiofibular joint
3. Inferior tibiofibular joint

Superior Tibiofibular Joint

• The superior tibiofibular joint is a plane synovial joint. It is formed between the head of the fibula and the lateral condyle of the tibia. It allows a small amount of gliding and rotational movement. These movements help adjust the position of the lateral malleolus during ankle movements.

Middle Tibiofibular Joint

• The middle tibiofibular joint is a fibrous joint. It is formed by the interosseous membrane, which connects the interosseous borders of the tibia and fibula. The fibers of the interosseous membrane run downward and laterally.

Openings in the Interosseous Membrane

1. The upper opening transmits the anterior tibial artery and veins.
2. The lower opening transmits the perforating branch of the peroneal (fibular) artery.

H6: Functions of the Interosseous Membrane

1. Provides attachment for the muscles of the leg.
2. Holds the tibia and fibula firmly together.
3. Resists the downward pull on the fibula produced by the peroneal (fibularis) muscles.

Inferior Tibiofibular Joint

• The inferior tibiofibular joint is a syndesmosis (fibrous joint). It connects the lower ends of the tibia and fibula through a strong interosseous ligament.
• It is reinforced by:
  • Anterior tibiofibular ligament
  • Posterior tibiofibular ligament
• The posterior tibiofibular ligament is stronger than the anterior ligament.
• Its lower, deep part forms the inferior transverse tibiofibular ligament, which strengthens the ankle mortise.
• This joint permits slight lateral rotation of the lateral malleolus during dorsiflexion of the ankle.

Innervation

• Superior tibiofibular joint:
  • Nerve to popliteus
  • Recurrent genicular nerve
• Middle tibiofibular joint:
  • Nerve to popliteus
• Inferior tibiofibular joint:
  • Deep peroneal (fibular) nerve
  • Tibial nerve
  • Saphenous nerve

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