A 38-year-old man presented to the emergency department with right ankle pain after an ankle injury. Because of high clinical suspicion of a fracture, a CT-scan was performed The patient did not attend any of the follow-up clinics and was lost to follow-up.
Coronal (Figure 1) and axial (Figure 2) CT images show a flake of bone in the soft tissues on the medial side of the medial malleolus representing an avulsion fracture of the insertion of the medial flexor retinaculum of the ankle. In this case, the avulsion fracture of the medial flexor retinaculum of the ankle was occult on X-ray. In addition, the CT-scan showed a fracture of the medial side of the talus.
Background The medial flexor retinaculum extends from the medial malleolus to the posterosuperior aspect of the calcaneus and forms the medial and posterior boundary of the tarsal tunnel [1,2,3]. The function of a retinaculum is to maintain approximation of tendons to the underlying bone [1,3]. The tarsal tunnel contains from anterior to posterior, the posterior tibial tendon, the flexor digitorum longus tendon, the posterior tibial artery, posterior tibial vein, and posterior tibial nerve, and the flexor hallucis longus tendon [4]. A focal density in the soft tissues can represent a foreign body, an ossification or a calcification [5].
Clinical Perspective Periosteal avulsion of the medial flexor retinaculum of the ankle is rare [2,6]. Injuries of the medial flexor retinaculum usually occur at the insertion on the medial malleolus [2]. Mechanisms of injury include forced ankle eversion and forced dorsiflexion combined with a contracted tibialis posterior tendon or acute injury of the ankle with fracture [2,3,6]. An important complication of an injury to the medial flexor retinaculum is anterior dislocation of the posterior tibial tendon [2,6].
Imaging Perspective An avulsion fracture of the medial flexor retinaculum of the ankle can be occult on X-ray [6]. CT is the best modality to visualize the bony flake. MRI with the ankle in different scan positions (i.e. imaging in motion) as dislocation of the posterior tibial tendon can be missed in static imaging. Ultrasound including dynamic manoeuvres can also be used to diagnose dislocation of the posterior tibial tendon [4,6,7].
Outcome The treatment of an avulsion fracture of the medial flexor retinaculum is conservative [2]. Unless posterior tibial tendon dislocation is present as well, in which case surgery is recommended [2,6].
Take Home Message / Teaching Points
When you notice a bony flake on the medial side of the ankle on X-ray or CT think of an avulsion fracture of the medial flexor retinaculum of the ankle.
When an avulsion fracture of the medial flexor retinaculum of the ankle is present, remember to check for dislocation of the posterior tibial tendon.
Avulsion fracture of the medial flexor retinaculum of the ankle
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Based on the provided ankle CT images, there appears to be a small bony fragment near the medial malleolus, located around the attachment site of the inner flexor retinaculum. The fragment does not show significant displacement. There is slight swelling of the soft tissue layer, but no obvious large-scale tearing. The overall structure of the articular surface’s bone is relatively intact, with no clear additional fracture lines or obvious signs of posterior tibial tendon dislocation. However, potential soft tissue injury at the attachment site of the medial flexor retinaculum should be considered.
According to the CT images, a bony fragment is observed on the medial aspect of the ankle joint, suggesting a possible avulsion injury involving the retinaculum or its attachment. This type of injury can occur with ankle sprains, external force, or when associated with other ankle fractures.
This should be differentiated from other types of small bony fragment injuries (such as avulsion of the medial malleolus or periosteal reaction) or potential foreign bodies (like calcifications or ossification lesions).
Considering the patient’s history of trauma, imaging findings, and literature reports, the most likely diagnosis is: Medial Flexor Retinaculum Avulsion Fracture. After excluding other fractures and tendon dislocations, there is no clear evidence of posterior tibial tendon dislocation at present. If dynamic dislocation is a concern, further investigation with dynamic imaging (MRI or ultrasound) could be considered.
For medial flexor retinaculum avulsion fracture, if the bony fragment is small and minimally displaced, conservative management is usually preferred:
If the fracture fragment is significantly displaced, or if there is instability/dislocation of the posterior tibial tendon, or if severe soft tissue injury compromises joint function, surgical intervention should be considered.
During or after conservative or surgical treatment, a gradual functional exercise program should be followed. Adhere to the FITT-VP principle (Frequency, Intensity, Time, Type, Volume, Progression):
If osteoporosis, poor cardiopulmonary function, or other chronic conditions exist, exercise intensity and methods should be adjusted in consultation with a medical professional.
Disclaimer:
This report is a reference analysis based on the current imaging and information provided, and cannot replace in-person clinical consultation or the opinion of a professional medical doctor. Patients should seek further evaluation and treatment from an orthopedic or related specialist based on their individual circumstances.
Avulsion fracture of the medial flexor retinaculum of the ankle
