Avulsion fracture of the medial tubercle of the posterior process of the talus: Three-dimensional (3D) computed tomography features

1. Introduction 

The talus is a unique bone because it has no muscle or tendon attachments and 70% of its surface is covered with cartilage [1], [2], [3]. Preservation of its anatomical integrity is critical for the function of the tibiotalar and the subtalar joints. Talus fractures comprise 3–5% of foot fractures and approximately 50% involve the talar neck [1]. However, osteochondral fractures and fractures of the processes are probably underreported because they are difficult to detect radiographically [4]. Misdiagnosis of these fractures or treatment as ordinary ankle sprains may be the cause of prolonged morbidity and disability.

Two processes, the posterior and the lateral, project from the body of the talus either of which may be fractured, as isolated injury or associated with other injuries [1], [2], [3].

Fracture of the medial tubercle of the posterior process is called Cedell's fracture [5], [6], [7], [8], [9]. The posterior talotibial and the posterior third of the deltoid ligament attach at the medial tubercle [10].

We present the case of an athlete with an isolated avulsion fracture of the medial tubercle of the posterior talar process and describe the application of two- and three-dimensional CT for establishing the diagnosis and for evaluating the fracture healing process. Although the injury is not underreported in the literature, the application and the diagnostic value of 3D CT has not been yet emphasized, to our knowledge.

2. Case report 

A 21-year-old international level long jump athlete presented 3 weeks following an ankle injury with complaints of posterior ankle pain on ambulation and movement of the joint. He suffered an injury to his right ankle during his training, when he landed on his dorsiflexed foot. The patient was treated initially by the team physician for ankle sprain but his symptoms persisted making ambulation difficult and training impossible. Initial routine AP and lateral ankle radiographs were interpreted as negative for bony lesion. On examination, severe tenderness over the posterior and medial ankle aspect anteriorly to the Achilles tendon was noted along with mild swelling. The range of motion of his right ankle and subtalar joints was restricted due to pain. Radiographic examination of the ankle (anteroposterior and lateral radiographs) revealed the presence of a fractured bone fragment at the posteromedial aspect of the talus (Fig. 1a and b). The lateral ankle radiograph was taken in 40° of external rotation revealing the location of the fracture. A two-dimensional (2D) computed tomography scan (CT) was obtained, which located the fracture site and showed the orientation of the fracture line (Fig. 2a and b). The presence of an isolated, minimally displaced and non-comminuted fracture of the medial tubercle of the posterior process of the talus was disclosed. Three-dimensional (3D) reconstruction of the ankle joint and the talus was undertaken to define the exact location and the size of the fragment and to delineate the relationship between the medial and the lateral tubercles (Fig. 3). Fracture displacement was less than 1mm and thus non-operative treatment deemed more appropriate. Treatment involved immobilization in a walking short leg cast for 6 weeks in 15° of plantar flexion. For the first 3 week partial weightbearing was recommended and the patient progressed gradually over the next 3 weeks to full weightbearing. Follow-up radiographic and 2D and 3D CT evaluation revealed consolidation of the fractured bony fragment in its anatomical position (Fig. 4, Fig. 5). The fracture line was not evident any more but the presence of immobilization osteopenia was striking on both plain X-rays and CT scans. An aggressive rehabilitation programme was followed aiming at restoration of the ankle and subtalar joint motion and improvement of the strength and proprioception of the lower limb joints. At latest follow-up, 27 months after the injury, the athlete had returned to competitive sports with success. The range of motion of his foot and ankle joints was restored to normal and no symptoms were reported.

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Fig. 1. (a and b) Anteroposterior and lateral radiographs in 40° of external rotation of the right ankle showing the fracture of the medial tubercle of the posterior process (white arrow).

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Fig. 2. (a and b) The fracture line is evident on a 2D CT scan (white arrow). After 2 months fracture line consolidation on a 2D CT scan is evident (white arrow).

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Fig. 3. The size and the precise location of the fracture are better shown on a 3D CT scan. C, calcaneus; mm, medial malleolus; lm, lateral malleolus; black star, lateral tubercle of the posterior process; white star and white arrow, medial tubercle of the posterior process.

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Fig. 4. (a and b) Anteroposterior and lateral radiographs of the right ankle after 8 weeks of immobilization. The fracture has healed (white arrow) but immobilization osteopenia is evident.

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Fig. 5. Three-dimensional reconstruction of the posterior aspect of the ankle showing healing of the fractured medial tubercle in anatomic position (white arrow). C, calcaneus; mm, medial malleolus; lm, lateral malleolus; black star, lateral tubercle of the posterior process; white star, medial tubercle of the posterior process.

3. Discussion 

Injuries to the talus may directly affect both the ankle and the subtalar joints and indirectly all other foot joints. The goal of talus fracture treatment is to maximize the movement of the ankle and subtalar joints, to restore the anatomical dimensions of the bone and to prevent arthritis [1], [2]. Fractures of the talar processes are not uncommon and account for 36% of all talar fractures [1]. The undersurface of the tubercles forms the posterior fourth of the subtalar joint and thus fractures in this location may affect the congruity of the subtalar joint [2].

The patient presenting with acute and chronic posterior ankle pain poses a diagnostic dilemma for the treating physician. The differential diagnosis includes many diseases or injuries [11]. Subtle talus fractures have a clinical presentation similar to ankle sprains. The mechanism of injury and the localized tenderness at the posteromedial aspect of the ankle assists in making the correct diagnosis.

The mechanism of injury of talar process fractures varies significantly. Lateral process fractures occur following rapid inversion and dorsiflexion, lateral tubercle fractures of the posterior talar process occur following excessive plantarflexion or forced inversion and medial tubercle fractures occur following dorsiflexion and pronation [5], [6], [7], [8], [9], [10]. Fractures of the entire posterior process and of the medial and lateral tubercles may be caused by direct or indirect trauma and are difficult to detect on standard ankle X-rays [12]. The entire posterior talar process is fractured in association with subtalar dislocation [1], [13] and may represent and obstacle to closed reduction [15].

In fractures of the medial process the flexor hallucis longus tendon may interpose between the fracture fragments, preventing healing and necessitating open reduction [16]. The fracture fragment may also displays causing tarsal tunnel symptomatology [9].

The Cedell fracture is more evident on a lateral ankle radiograph performed in 40° of external rotation, however it is more clearly delineated on a CT scan. The fracture may not be evident on a lateral ankle radiograph in neutral rotation or when the rotation is greater than 60°. Radiographs must be scrutinized closely to identify a fracture and high level of suspicion is necessary. The area of maximum point tenderness should be correlated with the radiographic findings. In fractures of the medial tubercle tenderness is localized at the area posterior to the medial malleolus, while in lateral tubercle fractures the tenderness is localized anterior to the Achilles tendon at the lateral aspect of the ankle.

When the diagnosis is unclear, the fracture is displaced and its size is significant, performance of a CT scan is indicated to demonstrate the fracture location, configuration and extent. The presence of an irregular line is evidence of an acute fracture, while presence of a sclerotic fracture line is anticipated in chronic fractures or non-unions [17].

Minimally displaced fractures, as in our case, may be treated conservatively, while dislocated and complex fracture commonly necessitate surgical fixation. Most reported cases in the literature describe sizable fragment, which along symptomatic, painful non-unions require fixation or excision of the fragment through a posteromedial approach [5], [6], [7], [8], [9], [10].

CT and MRI are used to detect radiographically occult fractures of the talus [17]. CT imaging is superior to plain imaging in showing the position and the direction of the fracture lines, the number and the relative position of the fragments and their relation to each other and with the articular surfaces. The direction of the fracture lines is better appreciated on the 2D CT scan, while the size, the morphology and the anatomical relationships are clearer on the 3D CT scan. Three-dimensional computed tomography is used as an adjunct to standard axial computed tomography in the evaluation of fractures of bones with complex anatomy. 3D reconstructions are a valuable advancement to 2D CT imaging and demonstrate the fracture more accurately, allowing the construction of a more precise preoperative surgical plan. Additionally, understanding of the fracture morphology is more complete. Progression of fracture healing can be evaluated with both 2D and 3D CT scans. MRI is the imaging method of choice when soft injury is suspected. In displaced fractures of the posterior tubercle of the medial process the tendon of the flexor halluxis longus may be interposed between the fragments and it has to be repositioned surgically. MRI has also the potential to show damage to adjacent ligaments and articular cartilage. CT and MRI are complementary imaging methods especially when there is doubt as to the extent of soft tissue damage.

In conclusion, the key to successful treatment is early diagnosis based on the mechanism of injury, a careful clinical examination and proper use of imaging techniques. 3D CT imaging offers more information than 2D CT and can be used to monitor fracture healing.