I have received two helpful comments from Drs. Andrew Kingzett Taylor and Atul Taneja
Actually, Andrew has been collecting very similar cases to the one I shared with longitudinal follow up.
His experience is compelling and strongly suggests that this case is post-traumatic, but unlikely due to the injury date (the MRI was obtained only 3.5 months after the injury date and the ossicle was already large and well formed and there was no deltoid ligament signal alteration).
He shared a relevant case in a 29M with posteromedial ankle pain, with imaging 1, 9 and 18 months post injury, and a classic Cedell’s fracture for comparison.
It seems like the case in the 29M started with a small cortical avulsion at the insertion of the posterior tibiotalar ligament (there is deltoid edema in at 1 month that resolves by 9 months, and the posterior swelling is pronounced in the Lat XR at baseline and subsequently resolves).
In his case, the post traumatic ossicle enlarges and matures over time….at 18 months it looks quite similar to the case I shared.
Atul’s comments are:
This topic reminds me that a few years ago some colleagues from my prior institution in Brazil published a paper with some cases with similar appearance. In their discussion, they present the following opinion (sorry about the long text):
The origin of such ossicles at the posteromedial talar tubercle is unknown, and we suggest that an analogy with the origin of the os trigonum could help to understand their pathogenesis. Because none of the present patients had had a history of relevant trauma, it is possible that unknown posteromedial ossicles were present and were detected only once they had become symptomatic. The posteromedial ossicle probably originated from a nonfused primary or secondary ossification center at this location. Ramsey et al (6) suggested the same etiology when describing their 2 cases, arguing that previously unknown isolated ossicles most likely explained the origin of the posteromedial ossicle. They defended this idea against the alternative hypothesis that a previous fracture was the cause, because in both of their patients, the posteromedial tubercle was intact on imaging and during surgery, and the ossicle appeared to be a distinct entity. A similar theory has also been advanced regarding the origin of the os trigonum (915) .
Trauma must also be considered in the pathogenesis of these ossicles. Repeated minor injury could lead to the presence of ossicles at the posterior talar tubercles (15) . Repetitive tension at the posterior talofibular and posterior talotibial ligaments might eventually detach the posterolateral and posteromedial tubercles, respectively, or prevent the ossification centers from fusing, again leading to ossicles. The patient would be unlikely to recall any particular trauma, and such unnoticed trauma could, perhaps, explain the pathogenesis of the ossicles we have described. Another possibility is that fractures can occur at the posteromedial talar tubercle 161718 , where they are known as Cedell fractures, and the ossicle could be a late finding after nonunion. Cedell (14) originally described 4 cases of osseous avulsion fractures of the posteromedial talar tubercle at the insertion of the posterior talotibial ligament. An analogy could be made with fractures of the posterolateral talar tubercle, known as Shepherd fractures (19) . However, none of our patients could recall a relevant traumatic event at the ankle, and such a hypothesis is less likely.
This is the reference – https://linkinghub.elsevier.com/retrieve/pii/S1067251614002464
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In my humble opinion, it is hard to tell if posttraumatic or not, but I am more prone to say it is a non-traumatic ossicle.
