Review Question - QID 3628

The patients hip radiograph demonstrates an os acetabuli marginalis superior which is a benign accessory ossification center found in the superior aspect of the acetabulum. This can be commonly confused with an acute fracture or avascular necrosis. Although the os acetabuli marginalis superior occasionally persists into adult life, it usually fuses to the acetabulum by the time an individual reaches age 20.

Caudle et al provide a case report of a a patient with a painful os acetabuli marginalis superior. This was successfully treated with resection of the fragment, and bone grafting. This was noted to be a very unusual source of hip pain in adolescents.

Incorrect Answers:
2-The fovea capitis is the depression on the head of the femur where the ligamentum teres inserts. This can appear as a small ossicle on the surface of femoral heads in skeletally immature patients. An example of this is shown in Illustration A.
3-Myositis ossificans is soft tissue calcification which develops after trauma, or more rarely, surgery. An example of myositis ossificans around the hip is shown in Illustration B.
4-Avascular necrosis of the femoral head classically occurs in patient with a history of alcoholism, steroid use, or sickle cell disease. Radiographs can demonstrate femoral head sclerosis, and eventually collapse of the articular surface. An example of femoral head AVN in a patient with sickle cell disease is shown in Illustration C.
5-Acetabular fractures occur in the setting of trauma, and are relatively rare in the pediatric population. An example of a left sided acetabular fracture is shown in Illustration D. Illustration E shows a right sided acetabular fracture through the triradiate cartilage.