Case 9
History:
27 year old female runner with progressive unilateral medial ankle pain
Findings:
MRI of the ankle showing presence of a type II accessory navicular that articulates with the navicular bone, with associated bone marrow edema and cystic changes around both sites of the articulation.
Diagnosis:
Discussion:
Accessory navicular ossicle, also called os tibiale externum, is related to the secondary ossification center at the navicular tuberosity. There are 3 types of accessory navicular with the type II (which is an ossification center adjacent to the tubercle of the navicular bone with a residual cartilaginous synchondrosis ) most commonly associated with medial foot pain. It is thought that a valgus stress injury may fracture the synchondrosis, resulting in abnormal bone marrow edema seen on MRI involving the accessory navicular and the adjacent navicular bone.
References:
- Lawson JP, Ogden JA, Sella E, Barwick KW. The painful accessory navicular. Skeletal Radiol. 1984; 12:250-262.
