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PH-MS07

Benign bone, cartilage and joint tumours

How age and site within a bone predict which benign tumour is present, how bone-forming, cartilage-forming and giant-cell-rich tumours and bone cysts arise and weaken bone, and why some recur or, rarely, turn malignant.

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  • 5 steps · 10 questions
  • 3D normal anatomy

By the end, you can

  • Use age, the region of the bone and the radiographic margin to explain where particular bone tumours arise.
  • Describe osteoma, osteoid osteoma and osteoblastoma, and explain the night pain of osteoid osteoma.
  • Explain how osteochondroma and enchondroma arise, their genes (EXT1/EXT2, IDH1/IDH2) and their risk of malignant change.
  • Explain how neoplastic stromal cells recruit giant cells in giant cell tumour of bone and tenosynovial giant cell tumour, and why these tumours recur.
  • Relate simple and aneurysmal bone cysts to pathological fracture.
  • Recognise the classic appearances, radiological signs of aggressiveness and tests of benign bone tumours, and explain how observation, ablation, curettage and denosumab act on each.

What it is

Benign bone tumours are neoplasms of bone, cartilage or the joint lining that do not metastasise, together with tumour-like lesions such as bone cysts. The WHO Classification of Tumours (5th edition) groups them by the matrix their cells make (bone, cartilage or neither) and separates truly benign tumours from intermediate ones, which are locally aggressive (giant cell tumour of bone, diffuse tenosynovial giant cell tumour) or rarely metastasise.

4 types to tell apart
Bone-forming
Osteoma (dense mature bone on the surface of the skull and facial bones), osteoid osteoma (a small painful nidus of woven bone) and osteoblastoma (the larger, often spinal, counterpart).
Cartilage-forming
Osteochondroma (a cartilage-capped outgrowth), enchondroma (cartilage within the marrow cavity) and chondroblastoma (an epiphyseal tumour of adolescents).
Giant-cell-rich and cystic
Giant cell tumour of bone (locally aggressive), aneurysmal bone cyst (blood-filled, USP6-driven) and simple bone cyst (fluid-filled, probably not a true neoplasm).
Joint and tendon sheath
Tenosynovial giant cell tumour, localised (tendon sheath nodule) or diffuse (formerly pigmented villonodular synovitis).

US spelling: tumours → tumors, tumour → tumor.

Normal function

A long bone: regions, cells and matrix

A long bone has four regions that matter for tumours. The epiphysis at each end lies beneath the joint cartilage. The physis (growth plate) is a disc of cartilage whose cells multiply and are replaced by bone, lengthening the bone until it closes in late adolescence. The metaphysis, the flared region beside it, is where new bone is laid down and remodelled fastest. The diaphysis is the shaft, a tube of compact bone around the marrow cavity.

Compact bone is built of : concentric lamellae around a central canal. Inside lies , whose spaces hold marrow, and outside is the , whose inner layer can make new bone. Osteoblasts lay down osteoid, an unmineralised collagen matrix that then mineralises; osteoclasts, multinucleate cells fused from monocyte-lineage precursors, resorb bone when stromal cells and osteoblasts signal through RANKL.

Benign bone tumours are far commoner than primary malignant ones; many are found by chance.

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