Osteosarcoma of Knee
CIM Case: Osteosarcoma of Knee
Clinical Scenario
Patient: 15-year-old male student Presentation: 6-month history of progressive pain and swelling around the left knee, worsening over time Relevant history: No history of trauma, no previous medical problems, no family history of cancer, no weight loss, no night sweats Examination findings:
- Visible swelling over distal femur, non-fluctuant
- Firm, tender mass fixed to bone
- Restricted knee flexion (90°, limited by pain and mass effect)
- No overlying skin changes
- No regional lymphadenopathy
- Popliteal pulse palpable but reduced compared to contralateral
- Full neurovascular status of foot
- No limp at rest, antalgic gait
Investigations Provided
Laboratory Results
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| WCC | 8.2 x10⁹/L | 4.0-11.0 x10⁹/L | Normal |
| Haemoglobin | 138 g/L | 130-175 g/L | Normal |
| Platelets | 310 x10⁹/L | 150-400 x10⁹/L | Normal |
| ESR | 28 mm/hr | 0-10 mm/hr | Elevated |
| CRP | 15 mg/L | <5 mg/L | Mildly elevated |
| ALP | 320 U/L | 40-150 U/L | Elevated (bone turnover) |
| LDH | 450 U/L | 120-250 U/L | Elevated (tumour marker) |
| Calcium | 2.40 mmol/L | 2.15-2.55 mmol/L | Normal |
| Creatinine | 65 µmol/L | 60-110 µmol/L | Normal |
Imaging
Image 1: AP and Lateral Radiographs of Left Knee
Radiological features:
- Large aggressive lesion in distal femoral metaphysis
- Mixed lytic and sclerotic pattern (osteoblastic predominant)
- Sunburst periosteal reaction
- Codman's triangle present
- Cortical destruction medially
- Soft tissue mass extending beyond cortex
- No pathological fracture
- Physis still open (skeletal immaturity)
- No skip lesion visible
Image 2: MRI Left Knee (T1, T2, and post-gadolinium)
MRI findings:
- Large tumour mass in distal femoral metaphysis (8 x 6 x 7 cm)
- Extension to within 2cm of physis but NOT crossing it
- No epiphyseal involvement
- Extra-osseous soft tissue mass (5cm maximum dimension)
- Neurovascular bundle displaced posteriorly but no encasement
- No skip lesions in femur
- No joint involvement
- Marrow oedema extends proximally 3cm beyond main mass
Image 3: CT Chest
CT findings:
- No pulmonary metastases
- No mediastinal lymphadenopathy
- Clear lung fields bilaterally
Image 4: Technetium-99m Bone Scan
Findings:
- Intense uptake in distal left femur
- No other areas of abnormal uptake
- No skip lesions
- No distant bone metastases
Questions & Model Answers
What is the likely diagnosis and what features on the X-ray support this?
What is your staging workup and what staging system is used?
How should the biopsy be performed and what are the key principles?
What is the role of chemotherapy and what is the treatment protocol?
What are the surgical options and how do you decide between limb salvage and amputation?
What is the prognosis and what factors influence outcome?
Key Teaching Points
Pattern Recognition
This pattern suggests Osteosarcoma:
- Adolescent with metaphyseal bone pain and swelling
- Sunburst periosteal reaction
- Codman's triangle
- Mixed lytic/sclerotic lesion with osteoid
- Elevated ALP and LDH
- Soft tissue mass
Comparison - Primary Bone Tumours in Adolescents:
| Feature | Osteosarcoma | Ewing Sarcoma |
|---|---|---|
| Age | 10-25 years | 5-20 years |
| Location | Metaphysis | Diaphysis (or flat bones) |
| Matrix | Osteoid (sunburst) | None |
| Periosteal | Sunburst, Codman's | Onion skin |
| Systemic features | Uncommon | Fever, elevated ESR (mimics infection) |
| Radiosensitive | No | Yes |
| Primary treatment | Surgery + chemo | Chemo + surgery/radiation |
Critical Management Points
- Biopsy at sarcoma centre - poorly placed biopsy may necessitate amputation
- Full staging before treatment - MRI, CT chest, bone scan
- Neoadjuvant chemotherapy is standard - MAP protocol
- Chemotherapy response is key prognostic factor - Huvos grading
- Limb salvage achievable in 85-90% - when wide margins possible
- MDT approach essential - orthopaedic oncology, medical oncology, radiology, pathology
Common Examiner Follow-ups
Q: "What if this patient presents with a pathological fracture?"
Pathological fracture in osteosarcoma:
- Historically considered indication for amputation (contamination)
- Modern approach: neoadjuvant chemotherapy, then reassess
- If fracture heals and good response, limb salvage may still be possible
- Worse prognosis than non-fractured tumours
- Higher local recurrence risk
Q: "What is the role of radiotherapy in osteosarcoma?"
| Role | Indication |
|---|---|
| Primary treatment | NOT standard - osteosarcoma is radioresistant |
| Positive margins | May be used if surgical margins positive |
| Unresectable disease | Palliation for axial tumours |
| Metastatic disease | Palliation for symptomatic metastases |
Contrast with Ewing sarcoma which is radiosensitive.
Q: "What about surveillance after treatment completion?"
Post-treatment surveillance focuses on:
- Local recurrence - clinical examination, MRI of operative site
- Pulmonary metastases - most common site, CXR or CT chest
- Late effects of chemotherapy - cardiac function, hearing, renal
- Prosthetic complications - loosening, infection, fracture
Detection of early pulmonary metastases allows potential curative metastasectomy.
Related Topics
- Ewing Sarcoma
- Chondrosarcoma
- Giant Cell Tumour of Bone
- Pathological Fractures
- Limb Salvage Surgery
- Endoprosthetic Reconstruction
- Bone Tumour Biopsy Principles