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Many cases of lipping of the posterior edge of the astragalus are seen, and a few cases of an extratarsal bone are observed; but these are rare. The case here reported is unique in that it shows an extreme projection from the posterior surface of the astragalus, with a separate joint for this projection on a corresponding projection of the os calcis. Consultation with the anatomic department at Cornell University revealed no similar finding in their records.
The surgical significance of this unusual finding is obvious in that a slight trauma might easily fracture this projection and cause considerable temporary disability. I saw one such case in consultation, but the extra articulation was not present. The posterior projection of the astragalus was almost as marked as in the case presented.
This patient was a laboring man who had received a fairly severe contusion of the foot, and the roentgenogram was
Farr CE. UNUSUAL ARTICULATION OF THE ASTRAGALUS AND THE OS CALCIS. JAMA. 1926;86(15):1128. doi:10.1001/jama.1926.26720410003010b