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Pathologic Fracture

Answer: C.

This child had a significant fracture after minor trauma.  His history, physical examination, and plain radiographs are concerning for osteosarcoma.  His xray shows typical findings: sclerosis of the distal metadiaphysis and a starburst periosteal reaction at the posterior metaphysis; some anterior periosteal reaction is also noted here.

Osteosarcoma is the most common primary bone tumor in children and young adults, with a peak incidence between 13 and 16 years of age, coinciding with the adolescent growth spurt.  It is more common in boys and those of African ancestry.  The most common sites in children are the metaphyses of long bones (75% are found in the distal femur), proximal tibia, and proximal humerus.

Interestingly, in adults osteosarcoma is a secondary neoplasm after transformation of Paget disease of bone, and in contrast involves the axial skeleton.  Other adult-onset risk factors include prior irradiation or chemotherapy and genetic syndromes such as Li-Fraumeni (familial cancer syndrome), retinoblastoma, and Rothmund-Thomson syndrome (skin atrophy, telangiectasias, cataracts, small stature).

The presentation of a fracture not associated with trauma, or fracture after trivial/minor trauma should alert the clinician to the possibility of a pathologic fracture.  During the workup (which may not be definitive in the ED), it is important to be aware of the differential diagnosis: Ewing sarcoma, lymphoma, Langerhans cell histiocytosis, osteomyelitis, stress fracture, osteoid osteoma, and unicameral and aneurysmal bone cysts.  This is especially helpful in counseling parents, as some of these are benign or require further investigation.

Although patients initially may present with subtle radiographic findings, plain films are a good screening tool for osteosarcoma (CT or MRI may help in unclear cases, or when suspicion is high based on history or epidemiology).  Staging is performed by MRI – it is important to note that the entirety of the long bone should be imaged.  Our patient’s  MRI shows enhancement of the tumor and surrounding soft tissue, consistent with osteosarcoma:

Picture
The treatment for osteosarcoma is initially medical: neoadjuvant therapy is started, followed by definitive surgical treatment (C).  

As discussed, this is not a typical fracture history or pattern (A, B).

Osteomyelitis (D) is on the differential diagnosis and should be considered; however, in the context of a dearth of other signs or symptoms (and radiographic findings consistent with mass), this is less likely.

Reference

Muchantef K, Pollock AN. Osteosarcoma of the Lower Extremity Presenting as a Pathologic Fracture. Pediatr Emerg Care. 2012; 28(9): 936-7.
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