Ankle radiograph

This webpage presents the anatomical structures found on ankle radiograph.

AP projection

The Ankle

The ankle joint is usually one of the most injured joints and the most common type of fracture treated by orthopedic surgeons⁽¹⁾. 

Although the ankle is often referred to as a single joint, it consists of the true ankle joint and the subtalar joint⁽²⁾.

The true ankle joint consists of three bones: tibia, fibula, and talus⁽³⁾. The tibia is larger and stronger than the two lower leg bones. It forms the ankle’s inner part.

Meanwhile, the fibula is the smaller bone of the lower leg. It forms the outer part of the ankle.

The talus refers to a small bone between the tibia and fibula and the calcaneus (heel bone).

The second joint—the subtalar joint—consists of two bones: the talus and the calcaneus⁽⁴⁾.

Ligaments, which refer to several strong connective tissue bands, hold the bones of the ankles together⁽⁵⁾. These ligaments include the anterior tibiofibular ligament, lateral collateral ligaments, and deltoid ligaments.

The anterior tibiofibular ligament is what connects the tibia to the fibula. The lateral collateral ligaments connect the fibula to the calcaneus, giving stability to the outsides of the ankles. 

Meanwhile, the deltoid ligaments attach the tibia to the talus and calcaneus and ensure stability on the insides of the ankles.

Different tendons also run through the ankle⁽⁶⁾. They attach muscles of the lower leg to the bones of the foot and the ankle. Some of the primary tendons include the Achilles tendon, flexor hallucis longus, and flexor digitorum.

The Achilles tendon helps connect the calf muscle to the calcaneus or heel bone⁽⁷⁾. Both flexor hallucis longus and flexor digitorum run along the inside of the ankle. However, flexor hallucis longus attaches to the big toe, while flexor digitorum attaches to the other toes.

The ankle joint’s primary function is to allow dorsiflexion and plantar flexion (movements) of the foot⁽⁸⁾. It also offers some degree of pronation and supination (up and down orientation of the foot) with subtalar and midtarsal joints.

Moreover, the joint serves as a shock absorber as the heel strikes the ground during the first phases of walking⁽⁹⁾.

Common Ankle Fractures

Ankle fractures result from the movement of the talus within the ankle mortise, with leverage exerted by the foot⁽¹⁰⁾. Common ankle fractures include lateral malleolus fracture, bimalleolar ankle fracture, and pilon fracture⁽¹¹⁾. 

A common kind of ankle fracture is lateral malleolus fracture⁽¹²⁾. It refers to a break of the lateral malleolus, the knob on the outside of the ankle joint.

Bimalleolar ankle fracture involves breaks of the lateral malleolus and the medial malleolus (the knob on the inside of the ankle)⁽¹³⁾. 

Pilon fracture refers to a fracture of the shinbone (tibia) near the ankle⁽¹⁴⁾. It is often a traumatic injury caused by a fall from a height.

Radiograph of the Ankle

Radiographic analysis of the ankle often includes three views: the anteroposterior view, the internal oblique view, and the direct lateral view⁽¹⁵⁾.

The anteroposterior view helps assess the ankle mortise through the lateral portions of the talus and tibiotalar joint overlap with the lateral malleolus⁽¹⁶⁾.

Anteroposterior ankle radiographs best evaluate the lateral process of the talus⁽¹⁷⁾. Moreover, this view is essential in assessing swelling in the medial or lateral malleolus.

Meanwhile, the internal oblique or mortise view evaluates the talus and all joint space margins⁽¹⁸⁾. 

The lateral view helps evaluate ankle effusions⁽¹⁹⁾. This view should include the proximal portion of the fifth metatarsal due to fractures in this region with ankle pain.

Moreover, the radiographic search pattern should assess the soft tissues for swelling⁽²⁰⁾. Swelling in the medial or lateral malleolus indicates underlying fractures or ligamentous injury.

Ankle joint effusions may be determined by the presence of a soft tissue density in the expected position of the fat lucency anterior or posterior to the ankle joint.

Radiography does not evaluate several ligaments and tendons of the ankle well⁽²¹⁾. However, the Achilles tendon is readily apparent.

The Achilles tendon’s average anteroposterior diameter is 6mm⁽²²⁾. A size over 8mm may indicate tendinosis or tearing, inflammatory arthropathies, or post-surgical change.

Other Ways to Evaluate Ankle Fractures

A computed tomography (CT) scan and magnetic resonance imaging (MRI) can help give a clear scope of ankle fractures⁽²³⁾. 

Computed tomography does not usually provide an initial assessment of the ankle⁽²⁴⁾. However, it can help evaluate the displacement of fractures and related dislocations and aid surgical planning.

MRI gives the highest soft-tissue contrast resolution of any imaging modality. It is essential in evaluating soft tissue abnormalities⁽²⁵⁾.

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1. Patel P, Russell TG. Ankle Radiographic Evaluation. [Updated 2020 May 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557462/ 
2. Arthritis Foundation. Ankle Anatomy. Retrieved from https://www.arthritis.org/health-wellness/about-arthritis/where-it-hurts/ankle-anatomy 
3. Ibid.
4. Ibid.
5. Ibid.
6. Ibid.
7. Ibid.
8. Senic, G. (2020, Oct. 29). Ankle joint. Retrieved from https://www.kenhub.com/en/library/anatomy/the-ankle-joint 
9. Ibid. 
10. Patel, P. (2020). Op Cit. 
11.  HSS. Ankle Fractures (Broken Ankle). Retrieved from https://www.hss.edu/condition-list_ankle-fractures.asp 
12. Ibid. 
13. Ibid. 
14. Ibid. 
15. Patel, P. (2020). Op Cit. 
16. Ibid.
17. Ibid.
18. Ibid.
19. Ibid.
20. Ibid.
21. Ibid. 
22. Ibid.
23. HSS. Op Cit.
24. Patel, P. (2020). Op Cit. 
25. Ibid.