Recognize the most common accessory ossicles in the hip and lower extremities Differentiate accessory ossicles from their most common misdiagnoses Recognize the different presentations of accessory ossicles through various imaging modalities

Accessory ossicles are unfused secondary ossification centers, separate from the adjacent bone. Unlike sesamoid bones, which function as friction reducers to protect tendons from injury, accessory ossicles are thought to be supernumerary bones without definite function. Most accessory ossicles are congenital, anatomical variants, but some rarely arise as a result from trauma or local degenerative disease. Symptomatic presentations are rare and thus a search for underlying pathology should be performed in these cases. Normally, however, accessory ossicles are typically clinically insignificant and found incidentally. Nonetheless,...

HIP AND KNEE Diagrammatic overview Fig. 1 and Fig. 2 Pictorial review Os acetabuli Prevalence: 3%[1] Location: Adjacent to the acetabular rim Overview:Or os acetabulare, an unfused secondary ossification center at the acetabular rim. Also thought to represent a rim fracture fragment secondary to a cam type femoroacetabular impingement (FAI). [2,3] Studies have proposed that “true” os acetabuli have cartilagenous growth plates more parallel to the joint surface, whereas FAI acetabular rim fragments growth plates are more perpendicular to the joint surface. [2,4] May be...

Accessory ossicles are secondary ossification centers separate from adjacent bone that may be clinically insignificant anatomical variants and vary in prevalence depending on the area of the body in which they are found. Familiarization with the most commonly encountered accessory ossicles in the hip and lower extremities is key in distinguishing an incidental, clinically insignificant, osseous structure from a more sinister misdiagnosis, which could entail unnecessary workup.

Alexandra Pérez Pérez, MD San Juan City Hospital, Transitional Year Department email: [email protected] ***Special thanks to my father, Dr. Javier Pérez-Andreu (Hospital Menonitas Caguas, Hospital Metropolitano las Lomas, Private Practice, Fajardo, PR), Dr. Elizabeth Trullenque (San Juan VA Hospital) and Dr. Jorge Vidal-Font (Hospital Pavia Santurce)for their support in the creation of this poster.***

[1] Asif Saifuddin, P. T. (2016). Musculoskeletal MRI, Second Edition. CRC Press. [2] R.J. Makanji, N. R. (2013). Rare and common ossicles of the lower extremity: Imaging manifestations and clinical implications. EPOS . Tampa, FL, USA: European Congress of Radiology. [3] Thomas Pope, H. L. (2014). Musculoskeletal Imaging. Elsevier Health Sciences. [4] Martinez AE, L. S. (2006). Os acetabuli in femoro-acetabular impingement: stress fracture or unfused secondary ossification centre of the acetabular rim? Hip Int. , 16 (4), 281-286. [5] Cecilia Pascual-Garrido, M. J.-D. (2016)....