Ortho Dx: Pain and swelling in the right knee

Osteosarcoma is the most common primary malignant bone tumor affecting approximately 560 children and adolescents each year in the United States. The prevalence has a bimodal distribution with the majority occurring in the second decade of life and a second...

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Osteosarcoma is the most common primary malignant bone tumor affecting approximately 560 children and adolescents each year in the United States. The prevalence has a bimodal distribution with the majority occurring in the second decade of life and a second peak occurring in elderly patients with Paget’s disease.

Classic osteosarcoma occurs during the adolescent growth spurt on the metaphyseal areas of long bones. The distal femur is the most common site of osteosarcoma, with the proximal tibia and proximal humerus being the second and third most common sites, respectively.

Patients typically present with weeks to months of progressive pain in the extremity that is involved. The pain is persistent during the day and night. Findings on physical examination may include decreased range of motion, erythema, and a palpable mass.

Anteroposterior and lateral x-rays of the extremity that is involved should be taken first. X-rays may show lytic destruction of metaphyseal bone with eventual cortical breakthrough. A Codman triangle, or a triangular area of new periosteal bone formation, may be noted at the diaphyseal end of the tumor. The tumor may expand into the soft tissue creating a sunburst pattern of new bone outside the bone that is involved.

Magnetic resonance imaging (MRI) of the entire involved bone should be performed if an osteosarcoma is present on x-ray. MRI determines the extent of soft-issue involvement, neurovascular involvement, and the presence of a “skip lesion” or a separate tumor found proximally. MRI also helps surgical planning to determine the location of safe margins and if a limb-sparing procedure is possible.

Once an osteosarcoma is suspected on x-rays, a biopsy is taken and examined before the definitive surgical procedure. The biopsy site is chosen from the area that will be removed during the definitive tumor resection. Osteosarcoma has several subtypes with varying characteristics including tumor aggressiveness, location, and prognosis. Intramedullary forms of osteosarcoma have 4 subtypes including conventional, telangiectatic, low-grade, and small-cell; conventional osteosarcoma is the most common type, accounting for 80% of all osteosarcomas. Surface osteosarcomas are divided into 4 subtypes including parosteal, periosteal, and high-grade.

Once the diagnosis of osteosarcoma is confirmed with imaging and biopsy, the tumor is staged based on factors such as tumor size, lymph node involvement, and distal metastases. Computed tomography of the chest should be performed in all patients with an osteosarcoma, as the lungs are the most common sites of metastases.

Treatment typically involves preoperative chemotherapy, wide surgical resection, and postoperative chemotherapy. Limp-sparing surgery, whenever possible, is the standard approach. Amputation may be necessary if the wide resection results in a nonfunctioning limb. Approximately 70% of patients without metastases will be disease-free after chemotherapy and wide-resection surgery. When a metastatic lesion is present, the 10-year survival rate drops below 30%.

Dagan Cloutier, MPAS, PA-C, practices in a multispeciality orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants (JOPA).

References

1. Messerschmitt PJ, Garcia RM, Abdul-Karim FW, Greenfield EM, Getty PJ. Osteosarcoma. J Am Acad Orthop Surg. 2009;17(8):515-527.
2. Wheeless III CR. Classic osteosarcoma. Updated June 7, 2012. Available at wheelessonline.com/ortho/classic_osteosarcoma