Bone

Bone is a scaffold it bears weight and occasionally gets infected.

Tumours often spread to bone and occasionally arise in bone. Bone tumours are dealt with in the bone tumours article.

Normal

• Normal bone has osteocytes.
  • If the osteocytes are missing... the bone is dead.

• Osteoblasts - make bone.
• Osteoclasts - destroy bone.

Memory device: 'b' before 'c'.

Hyperostosis frontalis interna

• Extra-thick frontal bone.
• No clinical significance -- just has to be recognized as a "nothing".

Bone marrow

Main article: Haematopoiesis

• Fat content (%) ~= age (in years)
  • e.g. 60 year old will have 60% fatty replacement.

• Should see three cell lines.
  • The cell lines:
    • Erythroid (red cells),
    • Myeloid (white blood cells),
    • Megakaryocytic (platelets).

Note: Lymphocytes are considered separately and typically spared in bone marrow failure.

Identifying the lines:

1. Megakaryocytes:
   • Big cells ~ 3x the size of a RBC.
2. Normoblasts (RBC precursors):
   • Hyperchromatic, i.e. blue, nucleus.
3. Myeloid line:
   • Granules.
   • Reniform nucleus, i.e. kidney bean shaped nucleus.

Images:

• Myeloid line (WC).

Organization

• Mature hematopoeitic cells at the centre (distant from bone).
• Immature hematopoeitic cells adjacent to the bone.

Infectious

Osteomyelitis

General

• Hematogenous - often in children.
• Direct entry (skin defect) - adults with diabetes.

Microscopic

• PMNs.

Chronic osteomyelitis

• Plasma cells.
  • May be sterile, i.e. no organisms.

Bone tumours

Main article: Bone tumours

This is a big topic. It is dealt with in a separate article.

The bone tumour article covers tumour mimics, e.g. brown cell tumour.

Fractures

Main article: Forensic pathology

This is dealt with in the forensic pathology article.

Others

The following is a collection of weird stuffs.

Paget disease of the bone

General

• Benign - unlike Paget disease of the breast.

Classically divided into three phases:

1. Lytic (predominantly osteoclasts).
2. Mixed lytic (osteoclastic) and blastic (osteoblastic).
3. Sclerotic (burned-out).

Clinical:

• Elevated ALP.

Microscopic

Features:

• Bone matrix has jigsaw-puzzle like pattern.
  • Jigsaw-puzzle pieces each ~ 100-500 micrometres in size (largest dimension).
• Increased osteoclast activity.
  • Osteoclast = macrophage that resorbs bone matrix.

Images:

• Paget disease - bone - high mag. (WC).
• Paget disease - bone - intermed. mag. (WC).

See also

• Hematopathology.
• Soft tissue lesions.
• Small round cell tumours.
• Chondro-osseous tumours.
• Cartilage.