Oncology: A Systematic Approach to Bone Tumours

Visual Element: An interactive "Zone of Transition" diagram, allowing users to slide between a "Narrow" (Benign) transition and a "Wide" (Malignant) transition, visualizing the difference in radiographic appearance.

Every orthopaedic surgeon, regardless of their subspecialty, will encounter bone lesions. Whether it's an incidental finding on a trauma series or a patient presenting with "night pain," the responsibility lies with you to initiate the correct workup. The stakes are incredibly high. A missed diagnosis can lead to loss of limb or life. A poorly planned biopsy can turn a limb-salvageable tumour into an amputation.

This guide provides a systematic, "safety-first" framework for the non-oncologist.

The Golden Rules of Orthopaedic Oncology

Before diving into pathology, etch these rules into your practice:

Rule #1: Do No Harm

A poorly planned biopsy or an inadvertent fixation of a pathological fracture without diagnosis disrupts tissue planes and spreads tumor cells. This can make a curative resection impossible.

Rule #2: Think Before You Cut

If you are performing a routine total hip replacement or fixing a fracture and encounter "abnormal" looking bone or tissue—STOP. Do not curette it. Do not ream through it. Take a sample for frozen section if available, or close the wound and image the patient.

Rule #3: Refer Early

There is no shame in referring a benign-looking lesion to a sarcoma centre. There is immense liability in sitting on a malignant one. When in doubt, phone a friend.

Part 1: Initial Assessment

The Clinical History: "Age is Everything"

In bone tumours, the patient's age is the single most powerful filter for your differential diagnosis.

• < 10 Years: Ewing's Sarcoma, Langerhans Cell Histiocytosis (LCH), Simple Bone Cyst (SBC), Metastatic Neuroblastoma.
• 10 - 30 Years: The Danger Zone. Osteosarcoma, Ewing's, Osteochondroma, Osteoid Osteoma, Chondroblastoma.
• 30 - 50 Years: Giant Cell Tumour (GCT), Chondrosarcoma, Lymphoma.
• > 50 Years: METASTASES (must be #1, #2, and #3), Myeloma, Chondrosarcoma. (Primary Osteosarcoma reappears here as a secondary transformation from Paget's).

Red Flag Symptoms:

• Night Pain: Pain that wakes the patient from sleep is a hallmark of malignancy (or Osteoid Osteoma).
• Constitutional Symptoms: Fevers, sweats, weight loss (think Ewing's, Lymphoma, Infection).
• Rapid Growth: A mass that doubles in size in weeks is aggressive.

Physical Examination

• Mass: Size, consistency (hard vs soft), mobility (fixed to bone?), depth.
• Nodes: Examine regional lymph nodes (rarely involved in sarcomas, except Epithelioid Sarcoma, Rhabdomyosarcoma, Synovial Sarcoma, Clear Cell Sarcoma -> Mnemonic: "ERSC").

Part 2: Plain Radiograph Analysis (The ABC'S)

You must act like a detective. Analyze the plain film systematically.

A - Location (Anatomic)

• Epiphysis: Giant Cell Tumour (GCT), Chondroblastoma ("Codman's Tumor"), Infection (Brodie's Abscess), Clear Cell Chondrosarcoma.
• Metaphysis: Most common site for primary tumors. Osteosarcoma, Osteochondroma, SBC, UBC.
• Diaphysis: Ewing's, Adamantinoma, Fibrous Dysplasia, Osteoid Osteoma.

B - Border (Zone of Transition)

This is the most reliable indicator of biological activity.

• Narrow Zone: You can draw a line with a sharp pencil where the tumor ends and normal bone begins.
  • Implies: Slow growth. Host bone has time to react (sclerosis). Usually benign.
• Wide Zone: The border is fuzzy, ill-defined, or permeative ("moth-eaten").
  • Implies: Rapid growth. Tumor is outpacing the host bone response. Aggressive/Malignant.

C - Components (Matrix)

What is the tumor making?

• Osteoid (Bone): "Cloud-like", "Fluffy", "Cotton-wool". -> Osteosarcoma.
• Chondroid (Cartilage): "Popcorn", "Rings and Arcs", "Stippled". -> Enchondroma / Chondrosarcoma.
• Fibrous / Lytic: "Ground glass" (Fibrous Dysplasia) or purely lytic (GCT, Metastasis).

S - Spicules (Periosteal Reaction)

The periosteum reacts to being lifted by tumor or pus.

• Solid/Buttress: Slow, benign process (e.g., Osteoid Osteoma).
• Onion Skin (Lamellated): Cyclical rapid growth. Layers of periosteum. -> Ewing's, Osteosarcoma.
• Sunburst / Hair-on-End: Rapid, disorganized growth along Sharpey's fibers. -> Osteosarcoma.
• Codman's Triangle: Periosteum lifted so fast it breaks, leaving a triangular cuff at the margin. -> Highly Aggressive.

Part 3: Staging (The Enneking System)

Once a lesion is identified, you must stage it before you touch it. Staging = Local (MRI) + Systemic (CT Chest + Bone Scan/PET).

The Enneking System (MSTS) remains the standard for surgical planning.

Benign Tumours

• Stage 1 (Latent): Static, heals spontaneously. (e.g., NOF). Intracapsular.
• Stage 2 (Active): Growing, expanding cortex. (e.g., ABC, UBC). Intracapsular but active.
• Stage 3 (Aggressive): Breaches cortex, invades soft tissue. (e.g., GCT). Extracapsular.

Malignant Tumours (Sarcomas)

Based on Grade, Site, and Metastasis.

• Stage I: Low Grade.
  • IA: Intracompartmental.
  • IB: Extracompartmental.
• Stage II: High Grade.
  • IIA: Intracompartmental.
  • IIB: Extracompartmental.
• Stage III: Any Grade with Metastases.

Part 4: The Biopsy - How Not to Mess It Up

The Mankin Study (1982, revisited 1996): A landmark paper showing that when biopsies were done by non-oncologists, complications occurred in 17.3% of cases, and unnecessary amputations occurred in 4.5%.

Biopsy Principles:

1. Placement: The biopsy tract is contaminated. It must be excised en-bloc with the tumor during definitive surgery.
2. Incision: Longitudinal incisions only (in line with the extremity). Never transverse.
3. Approach: Go through the muscle belly (direct route). Do not go between muscle planes (intermuscular intervals) or you contaminate the entire compartment.
4. Hemostasis: A hematoma tracks tumor cells. meticulous hemostasis is vital. Do not use a drain if possible.
5. Technique: Core needle biopsy (CNB) is now the gold standard (less contamination, high accuracy). Open biopsy is reserved for failed CNB.

Part 5: Top Diagnoses to Know

Benign

1. Osteoid Osteoma: Small nidus (<1.5cm). Intense night pain. Dramatic relief with Aspirin/NSAIDs. Tx: Radiofrequency Ablation (RFA).
2. Osteochondroma: Exostosis pointing away from the joint. Cartilage cap >2cm in adults suggests malignant transformation to Chondrosarcoma.
3. Giant Cell Tumour (GCT): Epiphyseal, lytic, eccentric. "Soap bubble". Can metastasize to lungs (benign mets). Tx: Curettage + Adjuvant (Phenol/Cement) +/- Denosumab.

Malignant

1. Osteosarcoma: Metaphyseal. Bimodal (Teens & Elderly). Osteoid matrix. Tx: Neoadjuvant Chemo -> Resection -> Adjuvant Chemo.
2. Ewing's Sarcoma: Diaphyseal. Small round blue cell tumour. t(11;22) translocation. CD99 positive. "Onion skin". Tx: Chemo -> Surgery/Radiotherapy.
3. Chondrosarcoma: Adults (>40). Pelvis/Femur. Chemo/Radio-resistant. Tx: Surgical Resection only.

Summary

The management of bone tumours is a multidisciplinary exercise involving radiologists, pathologists, and oncologists. Your role as the orthopaedic surgeon is to suspect the diagnosis, obtain the correct staging, and ensure the patient reaches the right hands without a compromised limb.

When in doubt: Image, Stage, Refer.