DR Anatomy & Structure of Bone

• Tissues in a bone

  • Connective tissue:

  - Supportive connective tissue: osseous tissue

  - 'Proper' connective tissue: periosteum, hyaline(hyaline = glass) cartilage.

  - Fluid connective tissue: blood and lymphatic fluid.

  
  

  • Epithelial tissue: endothelium of blood vessels.

  
  

  • Muscle tissue: smooth muscle in blood vessels.

  
  

  • Nerve tissue: neurons and glial cells.
• Macroscopic types of bone tissue

  • Cortical (aka Dense)

  - Most dense form, therefore appears brighter on radiography.

  - The 'outer' layer, the 'cortex'.

  - Strong.

  
  

  • Cancellous (aka Spongy or Trabecular)

  - Less dense, therefore appears darker on radiography.

  - Form the trabeculae of bone, surrounded by bone marrow.• Good combination of lightness and strength.

  
  

  • (Medullary cavity)

  - NOT a type of bone tissue or an empty cavity!

  - The most central part.

  - Contains bone marrow.

  
  

  • Periosteum (peri=around; osteum=bone).

  - Tough covering of dense connective tissue that surrounds the outside of the bone surface.

  
  

  • Endosteum (endo=inside).

  - Thin membrane lying in between the medullary cavity and cancellous bone.

  
  

  • Hyaline cartilage, highly specialised form of supportive connective tissue, lines the bones at joint surfaces.
• Periosteum


  • Outer layer of bone (except at joint surfaces).

  
  

  • Consists of two layers:

  - Fibrous (tougher) outer layer, assists in the attachment of tendons and ligaments to bone. Good vascular and neural supply.

  - Cellular inner layer, aka cambium/osteogenic layer. Much richer population of cells which can activate when healing required.

  
  

  • Perforating (Sharpey's) fibres: strong bands of collagen that anchor the periosteum to the underlying cortical bone

  
• Nutrient Foramen


  Located in long bones.

  
  

  • This is an opening in the periosteum and cortical bone for a nutrient artery.

  
  

  • Can mimic a fracture when seen obliquely.

  
• Endosteum


  • Simple thin membrane between medullary cavity and cancellous bone.

  
  

  • Lines trabeculae of cancellous bone.

  
  

  • Structure and function are similar to cellular layer of periosteum.

  
• Hyaline Cartilage


  • The avascular, a neural, hypocellular lining of bones in synovial joints.

  
  

  • Made of water, collagen, proteoglycans and sparse chondrocytes.

  
  

  • Surrounded by perichondrium, a dense connective tissue.

  
• Degenerative Joint Disease (osteoarthritis)

  DJD = breakdown of cartilage from middle age onwards, causing pain and stiffness.

  
  

  • Signs on XR:

  - Joint space narrowing.

  - Osteophyte formation.

  - Cortical sclerosis.

  - Subchondral cysts.
• Chondrocalcinosis


  Calcification of the cartilage

  
  

  - Calcium pyrophosphate deposition (CPPD) disease: crystals build up in cartilage, can lead to inflammation and cause cartilage damage.

  
  

  AKA 'pseudogout'. Like gout but not gout!

  
• Divisions of Long Bone

  Epiphyseal plate (aka physis): growth plate. In children this is made of cartilage so is radiolucent

  
  

  Diaphysis: Tubular 'shaft' of the bone

  
  

  Metaphysis: (meta = after). Narrow zone connecting the epiphyses to the diaphysis.

  
• Epiphysis


  • Ends of long bones.

  
  

  • Wider and deeper than diaphysis.

  
  

  • Cancellous bone covered by cortical bone.

  
  

  • Covered by hyaline cartilage at joint surfaces.

  
  

  • Red bone marrow in between trabeculae in femora and humeri.

  
• Epiphyseal plate


  - Growth plate

  - Cartilaginous in childhood (radiolucent/lytic)

  - Calcifies in adolescence(radiopaque/sclerotic)

  
  

  Radiologically indistinguishable in late adulthood.

  
• Metaphysis


  • Wider than the corresponding diaphyseal part of the bone.

  
  

  • Thinner cortical area and increased trabecular bone.

  
• Diaphysis


  • Most of the length of the bone.

  
  

  • Tubular with a thin lining of cancellous bone and thick 'collar' of cortical bone.

  
  

  • Central medullary cavity:

  - Red marrow (haematopoietic tissue) in childhood.

  - Yellow marrow (fat storage in adults).
• Elements of bone


  • Cells: Not many!

  
  

  • Extracellular Matrix:

  Osteoid: Unmineralised collagen. Relatively soft framework for deposition of...

  Mineral salts: calcium phosphate crystals, gives strength to bone.
• Rickets/Osteomalacia (adult version)


  Failure of osteoid to calcify due to Vit D deficiency.
• Bone cells


  Osteoblast:

  • Bone forming cell. Deposit osteoid and control mineralisation.

  
  

  Osteoclast:

  • Dissolves older bone.

  
  

  Osteocyte:

  • Modified osteoblast that is surrounded by newly formed bone.

  
• Microscopic structure of bone

  • Woven (immature) bone found in embryonic and neonatal skeleton. Collagen fibres are aligned randomly, rapid turnover of matrix.

  
  

  • Lamellar (mature) bone (lamina=thin plate): found everywhere else!

  Stress-orientated collagen fibres in thin sheets called lamellae. Fewer cells than woven bone.

  
  

  • Cortical bone is arranged into cylindrical structures called Haversian systems (aka osteons).

  
• Haversian systems


  • Haversian canal:

  central canal containing blood and lymphatic vessels and nerves, run parallel to long axis of bone.

  
  

  • Volkmann's canals:

  secondary canal sinter linking the Haversian canals, run perpendicular to long axis of bone.

  
  

  • Lacunae (lakes) spaces in the HS containing osteocytes(mature bone cells).

  
  

  • Canaliculi (little channels) allow the osteocytes to communicate with the rest of the HS.

  
  

  • Lamellae are concentric rings of bone matrix.
• Microscopic structure of cancellous bone

  • Trabeculae made up of parallel sheet of lamellae (rings of bone matrix), canaliculi and lacunae.

  
  

  • Covered in endosteum.

  
  

  • NO Haversian system.