I had to Google the term Talus Bipartitus as I was not familiar with it, but it is a congenital/developmental abnormality of the Talus. It is a relatively large, separate piece of the posterior Talus that can constitute up to one third of the posterior Talus. It is much larger than the Os Trigonum, which is a fairly common congenitally separate bone on the posterior margin of the Talus as well. Its code would be in the Q74 Code Set, with Q74.2: Other congenital malformations of the lower limb(s), which would include the "ankle joint," but also there is Q74.8: Other "specified" congenital malformations of the limb(s). I would probably go with Q74.8 since the diagnosis "Talus Bipartitus" is "specific" to the bone, not the joint.
Respectfully submitted, Alan Pechacek, M.D.
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