Summary

Osteosarcoma is the most common primary malignancy of bone in children and adolescents. It is defined by the production of malignant osteoid (immature bone) by tumor cells. It typically arises in the metaphysis of long bones (Distal Femur, Proximal Tibia) during the growth spurt. The classic presentation is persistent bone pain (mistaken for growing pains) and a mass. Radiological hallmarks include the "Sunburst" appearance and Codman's Triangle. It metastasizes early to the Lungs. Survival has improved dramatically from 20% to 70% with the advent of multi-agent chemotherapy combined with Limb Salvage Surgery. [1,2]

Key Facts

• Definition: Malignant tumour of mesenchymal origin that produces osteoid.
• Epidemiology: Bimodal.
• Peak: 10-20 years (Growth spurt).
• Secondary Peak: >65 years (Pagetic / Post-radiation).
• Location: "Away from the elbow, towards the knee". (Distal Femur 40%, Proximal Tibia 20%).
• Imaging: Sunburst Spiculation + Codman's Triangle.
• Metastasis: Lungs (80%). "Cannonball" metastases.
• Prognostic Factor: Response to Chemo (>90% necrosis).

Clinical Pearls

"Growing Pains Don't Swell": Growing pains are common, but they are bilateral, nocturnal, and have normal exams. If a child has UNILATERAL pain, a LIMP, or a MASS, you must X-ray. It is never "just growing pains".

"Codman's Triangle": This is not the tumour itself. It is the periosteum being lifted up by the expanding tumour so fast that it lays down a triangle of reactive bone at the edge. It signifies aggressive growth.

"The Whoops Procedure": If a surgeon mistakes an osteosarcoma for an abscess or benign cyst and performs a simple curettage/drainage, they contaminate the entire compartment. This forces an amputation instead of limb salvage. "If in doubt, REFER out". Never touch a bone tumour you don't understand.

"Skip Lesions": Osteosarcoma can jump within the marrow canal to a higher level in the same bone. You must MRI the entire bone, not just the lesion, to plan the resection level.

        SUSPICIOUS X-RAY
              ↓
    REFER TO SARCOMA CENTRE (Urgent <2w)
              ↓
    STAGING (MRI Joint to Joint / CT Chest)
              ↓
    BIOPSY (Core Needle)
              ↓
    NEO-ADJUVANT CHEMOTHERAPY (10 weeks)
    (Methotrexate, Doxorubicin, Cisplatin)
              ↓
    RESTAGING IMAGING
              ↓
    LIMB SALVAGE SURGERY (Wide Resection)
              ↓
    HISTOLOGICAL RESPONSE ASSESSMENT
    (% Necrosis)
              ↓
    ADJUVANT CHEMOTHERAPY
    (Tailored to necrosis rate)

1. Chemotherapy (The Game Changer)

• Before chemo, survival was <20% (micromets killed everyone).
• Neo-adjuvant: Shrinks tumour, makes surgery easier, and allows assessment of Tumour Necrosis Rate.
  • >90% Necrosis: Good responder. Continue same chemo.
  • <90% Necrosis: Poor responder. Change regimen (Add Ifosfamide/Etoposide).
• Agents: MAP regimen.
  • M: Methotrexate (High dose with Leucovorin rescue).
  • A: Adriamycin (Doxorubicin).
  • P: Platinol (Cisplatin).

2. Surgery (Wide Resection)

• Goal: Remove tumour with a cuff of normal tissue (Wide Margins).
• Limb Salvage (90% of cases):
  • Resect bone -> Reconstruct with Endoprosthesis (Mega-implant).
  • Or Allograft / Autograft (Fibula strut).
• Amputation: Reserved for:
  • Neurovascular encasement (cannot save leg).
  • Massive infection.
  • Displaced pathological fracture (Hematoma contaminates bed).

3. Radiotherapy

• Osteosarcoma is generally Radio-resistant. Radiotherapy has little role (unlike Ewing's).

Specific for musculoskeletal tumours.

• Grade (G):
  • G1: Low grade (rare).
  • G2: High grade (typical osteosarcoma).
• Site (T):
  • T1: Intracompartmental (inside bone).
  • T2: Extracompartmental (broken through cortex).
• Metastasis (M):
  • M0: None.
  • M1: Distant.

Most Osteosarcomas are Stage IIB (High Grade, Extracompartmental).

The Expandable Prosthesis ("Growable")

• In a 10-year-old, removing the distal femur growth plate causes a massive leg length discrepancy (often >10cm short).
• Solution: Non-Invasive Extensible Prosthesis (e.g., Repiphysis).
• Mechanism: Contains a magnetic motor. The child puts their leg in a magnetic coil machine in OPD, and the implant lengthens by 4mm painlessly. No surgery needed for lengthening.

Rotationplasty (Van Nes)

• Indication: Distal femur tumour in very young child where implant is not feasible, but sciatic nerve is intact.
• Concept:
  1. Resect distal femur and proximal tibia.
  2. Rotate the distal tibia/foot 180 degrees.
  3. Attach distal tibia to proximal femur.
• Result: The Ankle functions as a Knee joint. (Plantarflexion = Knee Extension).
• Pros: Functionally superior to above-knee amputation. Can run, jump, play sports. No phantom pain.
• Cons: Cosmetic appearance (foot is backwards at knee level). Psychological impact.

Key Studies

1. Rosen et al. (1970s): Introduced neo-adjuvant chemo, raising survival from 20% to 70%.
2. Meyers et al. (1992): Memorial Sloan-Kettering protocol. Established the importance of histologic response.
3. EURAMOS-1 Trial: Large international trial. Investigated adding Interferon/Ifosfamide for poor responders.

Survival Statistics

• Localized: 70% 5-year survival.
• Metastatic: 20-30% 5-year survival.

What is Osteosarcoma?

It is a cancer of the bone cells. The cells that normally build healthy bone have gone rogue and are building a messy, destructive tumour mass.

Why did my child get it?

It usually happens during the growth spurt when bone cells are dividing rapidly to make the child taller. Sometimes, a genetic mistake happens during this rapid division. It is not caused by an injury (though an injury often draws attention to it).

Will they lose the leg?

In the past, yes. Today, 90% of children keep their leg. We use powerful chemotherapy to shrink the tumour, then surgery to remove the bone and replace it with a high-tech metal implant.

What is the chance of cure?

If it hasn't spread to the lungs, the cure rate is about 70-75%. If it has spread, it is harder, but still treatable with surgery to remove lung nodules.

Q1: What are the radiological features of Osteosarcoma? A: Metaphyseal destruction, mixed lytic/sclerotic, Sunburst spiculation, Codman's Triangle, Soft tissue mass.

Q2: What is the most significant prognostic factor? A: The response to neoadjuvant chemotherapy, measured by the % of Tumour Necrosis in the resected specimen. >90% is good.

Q3: Describe the MAP regimen. A: Methotrexate (High dose), Adriamycin (Doxorubicin), Platinol (Cisplatin).

Q4: Differentiate Osteosarcoma from Ewing's Sarcoma. A:

• Osteosarcoma: Metaphysis, Osteoid producing, Sunburst.
• Ewing's: Diaphysis, Small Round Blue Cell (CD99+), Onion-skinning, t(11;22) translocation.

(End of Topic)