Talus Partitus


Axial CT-scan at the level of the talus	Sagittal reconstruction on the lateral aspect of the subtalar joint	Sagittal reconstruction on the medial aspect of the subtalar joint

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Like many accessory ossicles, this very rare anatomical variant is united through a synchondrosis to the talus, from which it arises. This synchondrosis is subject to stress, and micromotion results in shearing of the cartilage, development of marrow edema patterns at the apposing articulating surfaces, cystic changes, and pseudo-arthroses. A pseudoarthrosis is diagnosed by observing fluid-like signal on T2-weighted MR scans; its relationship to the patient's symptoms can be further studied by injecting lidocaine with fluoroscopic guidance.

The only differential diagnosis in this case is an os trigonum. However, an os trigonum is the result of a separate lateral tubercle of the posterior process of the talus. As such, it consists of a fragment of corticated bone attached to the posterior talofibular ligament, and located lateral to the flexor hallucis longus tendon. Notice that the case above shows a complete separation through a coronal cleft of both the medial and lateral tubercles of the posterior process of the talus from the rest of the bone.