Musculoskeletal Bone Disorders and Tumours

Benign Bone Tumours

Benign tumours are significantly more common than malignant ones (roughly 200 times more frequent). While they do not metastasize, they can still cause functional defects, pain, or pathological fractures.

• Osteoid Osteoma: A small benign tumour found on the surface of long bones or the skull. It is characterized by a core of osteoblasts and osteoclasts surrounded by sclerotic bone and typically causes severe, localized pain.
• Osteoblastoma: A larger, more "lytic" (bone-destroying) version of the osteoid osteoma.
• Giant Cell Tumour (Osteoclastoma): A tumour composed of multinucleated giant osteoclasts, usually located at the metaphysis/epiphysis junction of long bones. While benign, it is locally aggressive and can recur or even metastasize if the original tumour is surgically disrupted.

Malignant Bone Tumours (Sarcomas)

Malignant tumours, known as sarcomas, are highly destructive, tend to recur, and often metastasize to distant sites like the lungs.

• Osteosarcoma: The most common primary malignant bone tumour, often occurring around the knee. It involves malignant osteoblasts producing neoplastic bone and frequently affects the young (10–25 years) or the elderly.
• Chondrosarcoma: A malignant tumour arising from cartilage cells that expands and destroys bone.
• Ewing Sarcoma: A rare, highly malignant tumour primarily affecting children and young adults. It is often associated with a specific chromosomal translocation between chromosomes 11 and 22.
• Fibrosarcoma: A malignant mass composed of collagen and malignant fibroblasts, typically affecting the femur or tibia.

Secondary Bone Tumours

It is crucial to note that secondary (metastatic) bone tumours are actually the most common form of bone cancer. These occur when a primary cancer from another organ (such as the breast, prostate, lung, or kidney) spreads to the bone. Depending on the primary cancer, these can be:

1. Osteolytic tumours: Which destroy bone, leading to pathological fractures.
2. Bone-forming tumours: Which create areas of overly dense bone.
3. Mixed tumours: A combination of both.

Metabolic and Idiopathic Bone Disorders

Beyond infections and tumours, bone health is heavily influenced by metabolic processes and genetic factors.

Metabolic Conditions

• Osteoporosis: A condition where bone mass decreases due to an imbalance where resorption exceeds deposition. This is common in post-menopausal women due to decreased estrogen, which normally inhibits osteoclasts.
• Rickets and Osteomalacia: These result from inadequate mineralization of the bone matrix, usually due to Vitamin D or calcium deficiencies. Rickets occurs in children (affecting growth plates), while osteomalacia occurs in adults.
• Scurvy: A deficiency in Vitamin C, which is essential for collagen synthesis. This leads to defective bone matrix and weak blood vessels.

Idiopathic and Genetic Alterations

• Paget Disease of Bone: A chronic disease characterized by disorganized bone remodeling, where resorption and deposition occur at an accelerated, haphazard rate.
• Osteogenesis Imperfecta: Often called "brittle bone disease," this is a genetic disorder caused by abnormal Type I collagen synthesis.
• Osteopetrosis: A condition where defective osteoclasts fail to resorb bone, resulting in bones that are excessively thick and dense, yet paradoxically brittle.

Summary Table for Quick Review