Articular surfaces and ligaments
The lateral ligaments are three separate bands, not a single sheet like the deltoid ligament on the medial side. Each fans out from the lateral malleolus in a different direction, so each is tight in a different position of the foot.
| Ligament | Attachments | Tight in | Clinical test |
|---|---|---|---|
| Anterior talofibular (ATFL) | Front of the lateral malleolus to the lateral side of the talar neck | Plantarflexion | Anterior drawer |
| Calcaneofibular (CFL) | Tip of the lateral malleolus down and back to the lateral calcaneus | Dorsiflexion | Talar tilt (inversion stress) |
| Posterior talofibular (PTFL) | Malleolar fossa to the lateral tubercle of the posterior process of the talus | Dorsiflexion | Rarely torn alone |
The ATFL is the weakest and is a thickening of the capsule. The CFL is a round cord outside the capsule; it crosses both the ankle and the subtalar joint, and the fibular tendons run over its superficial surface. The PTFL is the strongest and runs almost horizontally.
Under the foot, the long plantar ligament runs from the plantar surface of the calcaneus to the ridge of the cuboid, with superficial fibres continuing to the bases of the lateral metatarsals. It turns the groove on the cuboid into a tunnel for fibularis longus and supports the lateral longitudinal arch.
The talus
The talus is the bone the lateral ligaments hold, and it carries the whole weight of the body from the leg to the foot. It has a body, a neck and a head.
- Talar dome (trochlea): the cartilage-covered upper surface of the body that sits in the ankle mortise, wider in front than behind.
- Talar neck: the narrowed part that points forwards and medially. The ATFL attaches to its lateral side, and most of the bone's blood supply enters through it.
- Talar head: the rounded front end that articulates with the navicular and rests on the spring ligament.
No muscle attaches to the talus. Its lateral process, which carries the lateral articular facet for the fibula, breaks when the dorsiflexed foot is twisted under load, the injury known as a snowboarder's fracture.
Relations: tendons of the lateral and dorsal foot
Two groups of tendons cross the lateral ankle: the fibular tendons behind the malleolus and the extensor tendons in front of it.
| Muscle | Insertion | Nerve |
|---|---|---|
| Fibularis longus | Crosses the sole in the cuboid groove to the base of the first metatarsal and medial cuneiform | Superficial fibular (L5, S1) |
| Fibularis brevis | Tuberosity at the base of the fifth metatarsal | Superficial fibular (L5, S1) |
| Fibularis tertius | Dorsum of the base of the fifth metatarsal | Deep fibular (L5, S1) |
| Extensor digitorum longus | Extensor expansions of the lateral four toes | Deep fibular (L5, S1) |
| Extensor digitorum brevis and extensor hallucis brevis | Long extensor tendons of toes 2 to 4; proximal phalanx of the great toe | Deep fibular (S1, S2) |
| Tibialis anterior and extensor hallucis longus | Medial cuneiform and first metatarsal; distal phalanx of the great toe | Deep fibular (L4, L5) |
Behind the lateral malleolus, fibularis brevis lies against the bone with longus behind it, both held by the superior fibular retinaculum. Below the malleolus they part at the fibular trochlea of the calcaneus: brevis passes above it and longus below. Fibularis longus and brevis evert the foot and brace the ankle against inversion; tertius is part of the anterior compartment and helps dorsiflex.
Clinical relevance
Most lateral ankle injuries are inversion sprains of the plantarflexed foot, and the ATFL fails first.
- Grading: grade I is a stretch, grade II a partial tear and grade III a complete rupture. Isolated ATFL tears are commonest; add a CFL tear with greater force.
- Chronic instability: repeated giving way after a sprain is treated with physiotherapy first, then anatomical repair of the ATFL and CFL (the Broström procedure).
- Fibular tendon subluxation: a tear of the superior fibular retinaculum lets the tendons flick forward over the malleolus, which is easily mistaken for a sprain.
- Fifth metatarsal fractures: an avulsion of the tuberosity follows an inversion injury and usually heals well. A Jones fracture, at the junction of the base and shaft, lies in a poorly supplied zone and is prone to non-union.
- Talar neck fracture: displacement disrupts the blood supply entering the neck, and the body can undergo avascular necrosis.
On the specimen
The two stations show the dorsum and lateral side of a dissected foot and a ligamentous preparation of the lateral ankle. On the ligament preparation, orient by the lateral malleolus: the band running forward is the ATFL, the cord running down and back to the calcaneus is the CFL, and the deep horizontal band behind is the PTFL.
On the tendon dissection, the tendon ending on the tuberosity of the fifth metatarsal is fibularis brevis; the thinner tendon ending on the dorsum of the same bone, further forward, is fibularis tertius. Extensor digitorum brevis is the fleshy belly on the lateral dorsum, and its most medial slip to the great toe is extensor hallucis brevis. Among the bones, the intermediate cuneiform is the shortest, so the base of the second metatarsal sits recessed between its neighbours. The fifth metatarsal is identified by the tuberosity projecting from its base.