A 19-year-old healthy female presented to the musculoskeletal oncology clinic with a chief complaint of the right-sided groin pain for 3 weeks. The pain was progressive in nature and atraumatic in origin. The patient noted significant pain with functional activity in addition to nighttime pain. Oral anti-inflammatory medications did not relieve the pain completely.
Radiographs were obtained by her primary care provider, which demonstrated a large, aggressive lesion with some mixed lytic and blastic features about the proximal femur (Fig. 1). On careful examination, there appeared to be a thin cortical rim over the margin of the lesion medially. Magnetic resonance imaging was obtained and demonstrated an aggressive appearing lesion centered near the inferomedial femoral neck as well as the lesser trochanter (Fig. 2). The lesion demonstrated a lytic appearance with some extension through the cortex. A soft tissue mass of approximately 6cm in size was present which abutted the iliopsoas and vastus musculature causing adjacent mass effect.
The patient underwent an open biopsy of the lesion through a posterolateral approach to the proximal femur. Sections from the curettage specimen showed a proliferation of relatively uniform large polygonal cells with eccentric round nuclei and abundant eosinophilic cytoplasm (Fig. 3). These cells were associated with the formation of new woven bone and seen growing in large sheets. By immunohistochemistry, the cells showed diffuse positive staining for SATB2, consistent with osteoblastic differentiation. Tumor necrosis was not present and mitotic activity was low (1-3 mitotic figures per 10 high-power fields). Overall, the morphologic features were consistent with an epithelioid osteoblastoma. After a diagnosis of epithelioid osteoblastoma was established, the patient returned to the operating room for extensive curettage of the lesion through a posterolateral approach followed by insertion of a short cephalomedullary intramedullary nail. Before insertion of the nail, an argon beam was used to ablate the curettage bony and soft tissue margin. Following insertion of the nail, the defect was then filled with allograft cancellous bone as well as demineralized bone matrix and the wound was then closed. The patient was made partial weight-bearing for a period of 6 weeks followed by full weight-bearing. Her pain was reported to be significantly relieved at the 6-week post-operative visit and she was ambulating with a mildly antalgic gait. One year post-operative imaging did not reveal any hardware complications or lesion recurrence (Fig. 4). In addition, on examination at the 1-year post-operative follow-up,the patient was not limited in gait or function. We will continue to follow the patient with serial radiographs and physical examinations for years to evaluate for recurrence.