Orthopaedic Bone Tumours: GCT, Osteosarcoma, and Ewing's Sarcoma
Methods of Treating Giant Cell Tumour (GCT)
In the management of Giant Cell Tumours, particularly those situated around the knee, several surgical and non-operative approaches are utilized depending on the aggressiveness and location of the lesion. Arthroplasty is a common procedure where the tumour is excised and an attempt is made to reconstruct the bone in some way. This reconstruction can be achieved using an autograft, such as using the patella to substitute for an articular defect, an allograft, which involves filling the defect with preserved bone from a cadaveric donor, or through the use of an artificial joint or prosthesis. For more aggressive tumours or cases where there is a high risk of recurrence, amputation may be necessary. In instances where surgical removal is not feasible, such as in certain vertebral locations, non-operative methods like radiotherapy may be employed. Radiotherapy is specifically noted as the primary treatment method for GCT affecting the vertebrae.
The site of the GCT often dictates the preferred method of excision treatment. For the lower end of the radius, the preferred treatment is excision with fibular grafting, as the opposite fibula is preferred because it resembles the distal end of the radius in shape. For the upper end of the humerus, lower end of the fibula, and lower end of the ulna, simple excision is the standard. In the lower end of the femur and upper end of the tibia, excision with Turn-o-Plasty is considered the treatment of choice. It is noted that recurrence following treatment is a serious problem, and with every subsequent recurrence, the tumour tends to become more aggressive.
Primary Malignant Tumours: Osteosarcoma
Osteosarcoma, also known as osteogenic sarcoma, is the second most common and a highly malignant primary bone tumour. It is pathologically defined as a malignant tumour of the mesenchymal cells, characterized specifically by the formation of osteoid or bone by the tumour cells. This tumour is subclassified based on the clinical setting of its occurrence and its dominant histomorphology. On the basis of the clinical setting, it is divided into primary and secondary types. Primary osteosarcoma is more common and typically occurs in the age group of years. This type has no known pre-malignant conditions and is significantly more malignant than the secondary form. Secondary osteosarcoma occurs in an older age group, from years onwards, and is often associated with pre-malignant conditions such as Paget’s disease, bone island, fibrous dysplasia, or history of irradiation to the bones.
Based on dominant histomorphology, osteosarcoma is classified into four types: osteoblastic (featuring significant new bone formation), chondroblastic (where the basic cell is a cartilage cell), fibroblastic (where the basic cell is a fibroblast), and telangiectatic (a predominantly lytic tumour). Regardless of these histomorphologic characteristics or the site of origin, all osteosarcomas are aggressive lesions that metastasize widely through the blood stream, with the lung being the most common site of metastasis. Involvement of the lymph nodes is unusual. The osteolytic type is generally more malignant than the osteoblastic type. Notably, despite its aggressive nature, osteosarcoma rarely penetrates an open physeal plate.
Clinical Features and Examination of Osteosarcoma
Most osteosarcomas fall into the primary conventional category, with the age at onset typically between years, making it the most common musculoskeletal tumour in this demographic. The most common sites of origin, in decreasing order of frequency, are the lower end of the femur, the upper end of the tibia, and the upper end of the humerus, although any bone may be affected. Pain is usually the first symptom reported by the patient, which is soon followed by swelling. The pain is described as constant and boring, worsening as the swelling increases. While a history of trauma may be mentioned, it is often incidental and merely serves to draw the patient’s attention to the swelling. Occasionally, the patient may present with a pathological fracture.
During examination, the swelling is typically found in the region of the metaphysis. Skin over the swelling may appear shiny with prominent veins, and the area is often warm and tender to the touch. The margins of the swelling are generally not well-defined. Movement at the adjacent joint may be limited, primarily due to the mechanical block caused by the swelling. The tumour mass may also compress neurovascular structures in the limb, leading to associated symptoms. While regional lymph nodes may be enlarged, they are usually reactive rather than involved by the tumour itself.
Radiological Features and Investigations
Radiological examination is crucial for diagnosis. X-rays typically show an area of irregular destruction in the metaphysis, which may be overshadowed by new bone formation. The overlying cortex is often eroded, and the lesion is typically permeative with a wide zone of transition from normal to abnormal bone. A characteristic periosteal reaction occurs as the tumour lifts the periosteum; this reaction is irregular, which distinguishes it from the smooth, layered reaction seen in osteomyelitis. Specific radiological signs include Codman’s triangle, which is a triangular area of subperiosteal new bone seen at the tumour-host cortex junction, and the "sun-ray appearance," which occurs as the tumour grows into overlying soft tissues and new bone is laid down centrifugally along blood vessels.
Laboratory and diagnostic procedures include the measurement of Serum Alkaline Phosphatase (SAP). While SAP is generally elevated, it is not of diagnostic significance; however, it is a useful parameter for follow-up. A rise in SAP after an initial fall following tumour removal is taken as an indicator of recurrence or metastasis. An open biopsy is the standard method for confirming the diagnosis. Fine needle aspiration cytology (FNAC) is not considered useful for the diagnosis of osteosarcoma, although core biopsy may be effective in advanced centres with expert histopathologists.
Treatment and Management of Osteosarcoma
The aim of treatment is to confirm the diagnosis through histology, where the presence of tumour new-bone formation is pathognomonic, and to evaluate the spread of the tumour through staging. Staging involves assessing the extent of involvement in the affected bone and the spread to other sites using X-ray and MRI. Complete removal of the tumour is vital, whether through limb-salvage surgery or amputation. Current advances in imaging and chemotherapy have made limb-sparing surgery the preferred option. This involves a "wide excision" of the tumour with a cuff of normal tissue, followed by reconstruction using a prosthesis, allograft, or autograft. Radiotherapy is reserved for inoperable cases as osteosarcoma is not sensitive to it.
Control of distant micro-metastases is essential, as they have often occurred by the time of diagnosis. Adjuvant chemotherapy has revolutionised treatment, typically started as "neo-adjuvant" chemotherapy before surgery and continued afterward. Common multi-drug combinations include high-dose Methotrexate, Ifosfamide, Cisplatin, and Adriamycin. These drugs are highly toxic and must be administered in specialized centres. Long-term follow-up occurs every weeks to detect recurrence or lung metastasis early. Without treatment, death typically occurs within years and often within months of detecting metastasis. Surgery alone offers a per cent -year survival rate, which increases to as high as per cent with adjuvant chemotherapy.
Secondary and Parosteal Osteosarcoma
Secondary osteosarcoma develops in bone already affected by pre-malignant diseases and is typically seen in patients over years of age. Its treatment follows the same lines as conventional osteosarcoma. Parosteal osteosarcoma is a distinct type arising in the region of the periosteum. It is a slower-growing, low-grade tumour usually seen in adults, with the common site being the lower end of the femur. Because it is low grade, chemotherapy is not indicated, and the prognosis is considered much better than that of conventional osteosarcoma.
Ewing's Sarcoma
Ewing’s Sarcoma is a highly malignant tumour occurring most frequently between the ages of years, though it can occur up to the age of . It commonly affects long bones ( of cases), particularly the femur and tibia, while the remaining of cases involve flat bones like the pelvis and ribs. It is known for its multicentric origin. The tumour typically begins in the diaphysis of the long bone. Gross pathology shows the tumour involving a large area or even the entire medullary cavity. The tissue is soft, friable, and may be thin, sometimes appearing liquid. As the tumour grows, the bone may expand, and the periosteum may show subperiosteal new bone formation. The tumour eventually ruptures through the cortex and extends into the soft tissues. Histopathologically, it is characterized by sheets of uniform, small round cells that resemble lymphocytes, often forming rosettes around a central clear area. This tumour grows rapidly and metastasizes early through the bloodstream to the lungs and other bones. Clinical features include pain and swelling, often with associated fever and malaise, which sometimes leads to it being confused with osteomyelitis.