Os sustentaculi

Last revised by Joachim Feger on 28 Dec 2021

The os sustentaculi or os sustentaculum is a rare accessory ossicle of the ankle and a normal anatomical variant.

The estimated prevalence is approximately 0.3-0.4% 1.

It has been found in up 24% of talocalcaneal coalitions 2.

The os sustentaculi is usually found at the posterior aspect of the sustentaculum tali and is connected to the latter by a fibrous or fibrocartilaginous synchondrosis 3,4.

A bony bridge between the posterior aspect of the sustentaculum and the talus has been suggested as a variant of the os sustentaculi.

The os sustentaculi can be best visualized on an AP view of the ankle with a slight amount of external rotation 4.

The os sustentaculi can be nicely visualized on CT and might demonstrate degenerative changes such as irregular or hypertrophic cortical contours, subchondral cysts or vacuum phenomenon 3.

On MRI of the ankle, the os sustentaculi can be visualized as a separated bony structure from the sustentaculum.

Degenerative changes of the synchondrosis with contour irregularities, sclerosis, and cyst formation might occur. Bone marrow edema might be present if the patient experiences symptoms and pain 1-3.

The os sustentaculi was first reported by the German anatomist Wilhelm Pfitzner in 1896 2-6.

An os sustentaculi can cause pain, e.g. as a result of overuse, and might be mistaken for a sustentaculum fracture, an unusual exostosis or os calcanei secundarium 1-5.

The os sustentaculi has been related to an extra-articular talocalcaneal coalition (see Case 1) and can cause pain in the setting of overuse 1,2.

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