The patient was admitted with a rotational ankle injury.
The patient was admitted with a rotational ankle injury. MRI examination was performed to look for ligamentous disruption. A bone bruise at the talar dome and soft tissue oedema were the only post-traumatic findings. However, coalition was also detected between the navicular and cuboid tarsal bones. The patient reported no history of clinical problems related with this entity.
Tarsal coalitions are rare but well-known entities with many forms. Talocalcaneal and calcaneonavicular types are the most commonly encountered. Cubonavicular tarsal coalition is very rarely seen, in less than 1% of all cases. It may cause clinical findings such as peroneal spasm, especially in the adolescent period, but may be asymptomatic as in this case.
Coalition of the tarsal bones can be of an osseous, cartilagenous or fibrous nature. CT examination is the preferred modality for coalitions. In this case, CT examination was performed to confirm the diagnosis. MRI findings were suggestive of a fibrous nature, however CT showed osseous coalition. Awareness of MRI findings is necessary for reaching a diagnosis confidently, even in very rare forms as in this case.
Cubonavicular coalition
Based on the patient's CT and MRI examination results, an abnormal bony or soft tissue connection is observed at the medial aspect of the foot (primarily between the navicular and the cuboid) at the tarsal joint surface. The specific characteristics are as follows:
Combining the patient’s clinical presentation (32-year-old female admitted due to an ankle sprain) with the imaging findings above, the possible diagnoses or differential diagnoses include:
This is very rare clinically, accounting for less than 1% of all tarsal coalition cases. It may lead to restricted joint mobility or mild foot deformity. In adolescents, it can be associated with Achilles or peroneal muscle spasm.
For instance, talocalcaneal or calcaneonavicular coalition. However, the corresponding areas show no obvious abnormality on imaging, so these are less likely.
Chronic injury or inflammation may cause destruction of the joint surfaces or focal ankylosis. However, on CT, one would usually see bony destruction or marginal changes, which are not entirely consistent with this form of coalition.
Taking into account the patient’s clinical presentation (rotational sprain upon admission, without typical foot symptoms) and imaging findings (MRI indicating fibrous changes, but CT confirming bony bridging), the most likely diagnosis is:
Cubonavicular Tarsal Coalition, predominantly with a bony connection.
This patient’s coalition site is clearly shown on both MRI and CT, aligning with most documented forms of coalition. It has been discovered incidentally, as the patient is mildly symptomatic or asymptomatic.
Given the patient’s current condition (mild or asymptomatic), a gradual exercise program can be undertaken. The focus is to strengthen the muscles around the ankle and foot, maintain joint flexibility, and prevent re-injury.
Throughout the rehabilitation process, regular follow-up is necessary. Observe any pain, swelling, or discomfort before and after exercise. If any deterioration occurs, training should be adjusted or paused promptly.
Note: Due to the presence of tarsal coalition to some degree, high-impact running, jumping, or twisting movements should be performed with caution to prevent compensatory injury to adjacent joints.
Disclaimer: This report is for reference purposes only and does not replace a face-to-face consultation or professional medical advice. If there are any changes in your condition or discomfort, please seek medical care promptly.
Cubonavicular coalition
