Swelling of the lower thigh.
The patient presented to the emergency department with a one-week history of swelling of the lower right thigh. There had been no direct trauma, but the patient had attended a football training weekend one week previously. Examination revealed a swelling medial on the right thigh, just above the knee. There was no erythema and knee movements were normal. The patient underwent ultrasound scanning initially to exclude a haematoma. This revealed a well-vascularised mass arising from the femur (Fig. 1), raising the strong possibility of a malignant bone tumour.
A plain film revealed all the classic signs of an osteosarcoma: bone destruction, new bone formation with a "sun ray" pattern, Codman's triangle (periosteal elevation at the edge of the tumour) and a soft tissue mass (Fig. 2). Subsequent MRI scanning revealed an intramedullary mass in the metaphysis of the femur with a breach of the cortex and a large extramudullary component (Fig. 3).
There were no signs of skip lesions in the rest of the femur or upper tibia. A plain chest film was normal. A biopsy confirmed the diagnosis of high-grade conventional osteosarcoma. Chemotherapy was initiated.
Though not a common tumour overall, representing just 0.2% of all malignant tumours, osteosarcoma is the second most frequent primary malignant neoplasm of bone after myeloma. The peak incidence of primary osteosarcoma is between 10 and 25 years of age and it is more common in males. Osteosarcomas can also arise secondarily in long standing Paget's disease and after radiation exposure. The tumour tends to metastasise early to the lungs and, less commonly, spreads to regional lymph nodes; there is also a 25% incidence of "skip" metastases, which are simultaneous foci of osteosarcoma either within the same bone or across an adjacent joint. Around 75% of osteosarcomas are of the classic or conventional type and they arise most commonly in the metaphysis of a long bone with 50–75% occurring around the knee.
Plain radiography is still the examination of choice in the initial assessment of a bone tumour. Classic osteosarcoma is typically seen as an ill-defined intramedullary lesion in the metaphysis, with extension through the cortex and formation of a soft tissue mass. Most commonly both bone destruction and formation are present, though purely osteolytic or osteosclerotic lesions can occur. Rapid formation of immature bone leads to the "sun ray" appearance. Periosteal reaction in the form of Codman's triangle is also common.
Scintigraphy has been shown to commonly overestimate the extent of malignant bone tumours and this role has been taken over by CT and MRI. CT is also the best modality for detecting lung metatases.
Today MRI has a central role in the assessment of malignant bone tumours. It is the best modality for local staging as it shows well both the intra- and extraosseous extent of the tumour, as well as neurovascular, epipyseal and joint involvement. Scanning of the whole bone is used to exclude skip lesions. MRI also plays a key role in assessment of response to chemotherapy and follow-up after surgery. Gadolinium enhancement is primarily used to monitor tumour response. Treatment of osteosarcoma consists of a combination of neoadjuvant chemotherapy and surgery, which in 90% of cases now is a limb sparing procedure. Advances in imaging, chemotherapy and surgery have led to a dramatic improvement in the prognosis of osteosarcoma over the last two decades, with a rise from 5% 5-year survival to around 50-75% today.
Classic osteosarcoma
According to the provided X-ray and MRI images, the following main features can be observed:
• The lesion is located in the distal femoral metaphyseal-epiphyseal region (near the knee), with an irregular shape.
• X-ray shows both bone destruction and new bone formation, with the soft tissue mass expanding into surrounding tissues. A “sunburst” periosteal reaction and a possible Codman’s triangle can be noted locally.
• MRI shows the tumor extending inside and outside the bone marrow. On T2-weighted sequences, it presents mixed high signal intensity, with visible soft tissue invasion, and localized enhancement of blood flow signals.
• Imaging suggests cortical bone involvement and extension into soft tissues. Attention should also be given to the possibility of skip lesions, but currently, images show the lesion confined to the same region.
Considering the patient’s age (15 years), gender (male), chief complaint (distal femoral swelling and pain), and the aforementioned imaging findings, the possible diagnoses include:
1) Osteosarcoma: Typically occurs in adolescents aged 10–25 years, commonly around the knee joint. X-ray commonly shows combined bone destruction and immature bone formation, often with a “sunburst” periosteal reaction and a soft tissue mass.
2) Ewing Sarcoma: Also common in adolescents, often presents with an “onion skin” periosteal reaction, which is not fully consistent with the “sunburst” change in this case.
3) Chronic Osteomyelitis: May display bone destruction and sequestra, but generally involves prominent infection and inflammation; imaging might show sclerotic bone, sinus tracts, or abscesses.
4) Chondrosarcoma: Usually seen in older patients, and imaging often shows ring- or arc-like calcifications of cartilaginous matrix, which does not entirely match this patient’s age and the aggressive new bone formation.
Considering the patient’s age, symptoms, and characteristic X-ray and MRI findings—along with the common location and radiologic features of osteosarcoma—the most likely diagnosis is Osteosarcoma.
A biopsy and pathological examination are required for definitive confirmation and to determine the tumor’s histological subtype and grade.
Treatment Strategy:
• Neoadjuvant Chemotherapy: Administered before surgery to shrink the tumor and enhance complete surgical resection.
• Surgery: Currently, approximately 90% of patients can undergo limb-salvage surgery (tumor segment resection and reconstruction) to preserve limb function.
• Adjuvant Chemotherapy: Administered postoperatively to reduce local recurrence and metastatic risk, thereby improving survival.
• Imaging Follow-up: Regular MRI and chest CT scans are recommended to monitor for local recurrence and lung metastases.
Rehabilitation and Exercise Prescription:
• Preoperative Rehabilitation: If pain allows, gentle range-of-motion exercises (e.g., seated knee flexion-extension) and low-intensity muscle strengthening can be performed, while avoiding high-load weight-bearing.
• Early Postoperative Rehabilitation: Under the guidance of professional rehabilitation therapists:
- Exercise Frequency: 3–5 times per week.
- Exercise Intensity: Initially focus on non-weight-bearing or minimal weight-bearing on the affected limb, with aids such as crutches or walkers.
- Exercise Duration: Approximately 15–20 minutes per session, gradually increasing based on pain control and tolerance.
- Exercise Modalities: Range-of-motion exercises, isometric quadriceps training, core stability exercises, etc.
• Mid- to Late-stage Rehabilitation: With adequate bone and soft tissue healing, gradually increase weight-bearing on the affected limb and overall exercise load:
- Exercise Frequency: 3–5 times per week, potentially increasing to 5–6 times depending on tolerance.
- Exercise Intensity: Progress from minimal to partial or full weight-bearing in a stepwise manner under medical/therapist evaluation.
- Exercise Duration: May extend to 30 minutes or more per session.
- Exercise Modalities: Water-based walking, stationary cycling, progressive resistance exercises, etc.
• Throughout rehabilitation, ensure balanced improvements in limb strength, joint mobility, and overall cardiopulmonary endurance. Avoid overstress on a single area. If pain or discomfort occurs, promptly reassess and adjust the plan.
Disclaimer:
This report is solely based on the provided images and information for reference and cannot substitute for an in-person consultation or professional medical advice. If there are any concerns or worsening symptoms, please seek prompt medical care for an individualized treatment plan.
Classic osteosarcoma
