What is the diagnosis for a patient with a right ankle X-ray showing probable os trigonum versus a less likely fracture of the posterior talus, with preserved joint spaces and no radiographically appreciable soft tissue abnormality?

Differential Diagnosis for Right Ankle X-ray Findings

Single Most Likely Diagnosis

• Os trigonum: This is considered the most likely diagnosis due to the radiographic findings indicating a probable os trigonum, which is a common accessory bone in the ankle. The os trigonum can sometimes cause pain and tenderness, especially if it is fractured or if there is an overuse injury.

Other Likely Diagnoses

• Fracture of the posterior talus: Although considered less likely than os trigonum, a fracture of the posterior talus is still a plausible diagnosis given the radiographic findings. The location and nature of the pain and tenderness would need to be correlated to confirm this diagnosis.
• Ankle sprain: Although not directly mentioned in the radiographic findings, an ankle sprain could be a cause of pain and tenderness in the ankle region and might not always show significant radiographic abnormalities, especially if it's a ligamentous injury without a fracture.

Do Not Miss Diagnoses

• Talus fracture with subtle displacement: It's crucial not to miss a fracture of the talus, as it can have significant implications for ankle stability and function. Even if the initial X-ray suggests a less likely fracture, clinical correlation and possibly further imaging (like CT scans) might be necessary to rule out a subtle fracture.
• Osteochondral lesion of the talus: This condition involves a piece of cartilage and bone becoming damaged or torn off, which might not be immediately apparent on a plain X-ray. It's a critical diagnosis to consider due to its potential for long-term ankle dysfunction.

Rare Diagnoses

• Coalition of the talus and calcaneus: This is a rare congenital condition where there's an abnormal connection between the talus and calcaneus bones. It could potentially cause ankle pain and might be considered if other diagnoses are ruled out.
• Tumor of the talus or surrounding bones: Although extremely rare, a tumor could cause pain and abnormalities in the ankle region. Advanced imaging would be required to investigate this possibility further.