History

An 11-year-old boy presented with an 8-month history of right tibial pain. Initial diagnosis was patellar tendonitis. After failing to respond to non-steroidal anti-inflammatory medications and activity modification, radiographs were obtained (Fig. 1). Past medical history was unremarkable. Physical examination revealed a waddling gait with a limp on the affected side. His sensory, motor, and vascular examinations showed no deficits. He had a full range of motion of the knee and the primary knee ligaments were intact. There were no palpable inguinal lymph nodes. Laboratory studies obtained at his initial evaluation were notable for normal calcium, PTH, and 1,25-hydroxy vitamin D values; phosphorus and 25-OH Vitamin D levels were both mildly decreased.

Fig. 1
figure 1

a Anteroposterior and b lateral radiographs of the tibia and fibula

Magnetic resonance imaging (MRI) and a Technetium-99 bone scan were performed (Figs. 2, 3). A core needle biopsy was performed and was interpreted as conventional osteosarcoma by the pathologist at the referring institution (Fig. 4).

Fig. 2
figure 2

a T1-weighted coronal and b sagittal images (repetition time/echo time, 734/21), c T2-weighted axial image with fat suppression (repetition time/echo time, 5,320/78), d T1-weighted axial image with fat suppression and gadolinium contrast material (repetition time/echo time, 560/21)

Fig. 3
figure 3

Whole-body technetium 99 m bone scan

Fig. 4
figure 4

a Low power (×40, H and E) and b higher power (×400, H and E) histological images

What is the diagnosis?