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
Q1
What is the likely diagnosis and what features on the X-ray support this?
Q2
What is your staging workup and what staging system is used?
Q3
How should the biopsy be performed and what are the key principles?
Q4
What is the role of chemotherapy and what is the treatment protocol?
Q5
What are the surgical options and how do you decide between limb salvage and amputation?
Q6
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