Bone

Bone

• Bones work with muscles and joints to form the musculoskeletal system.
• The skeleton helps to hold the body together and enables movement.
• Bones can come in five different types: long bones, short bones, flat bones, irregular bones, and sesamoid bones.

Bone Structure

• Bone is one of the hardest tissues in the body when fully developed.
• Bone consists of:
  • Organic material (40-50%): mainly collagen
  • Inorganic material (30-40%): mineral salts, such as calcium and phosphate
  • Water (~20%)
• Bone is a vascular tissue with a large capacity for growth in the first two decades of life and the ability to regenerate throughout life.
• There are three key types of bone cells:
  • Osteoblasts: Single-nucleus, immature bone cells that form bone.
  • Osteocytes: Mature bone cells that originate from osteoblasts that become trapped in lacunae.
  • Osteoclasts: Multi-nucleated bone resorption cells that help maintain bone shape by breaking down bone tissue.

Bone Development

• Bone development starts before birth and completes around age 25.
• It involves two main types of ossification:
  • Intramembranous ossification: Bone develops directly from mesenchymal tissue.
  • Endochondral ossification: Bone develops from cartilage models.

Types of Bone Tissue

• There are two main types of bone tissue:
  • Compact bone: appears solid and contains numerous Haversian systems.
  • Cancellous bone: also known as spongy bone, appears spongy with red bone marrow and trabeculae.

Bone Structure: Osteon

• The basic structural and functional unit of bone is the osteon, also known as the Haversian system.
• Each osteon contains a central Haversian canal running longitudinally through the system, which houses blood vessels, lymph, and nerves.
• The Haversian canals are surrounded by concentric rings of bone known as lamellae.
• Between the lamellae are spaces called lacunae, which contain lymph and osteocytes.
• Canaliculi link the lacunae to the lymph vessels, providing nourishment to osteocytes.

Bone Structure: Periosteum

• The surface of bone is covered by the periosteum, a vascular fibrous membrane.
• The periosteum functions to:
  • Provide nourishment through blood vessels to the bone.
  • Provide attachment points for muscle tendons.
  • Assist in bone formation and repair.

Bone Healing

• Bone healing involves several stages:
  • Formation of fibrocartilaginous callus: During the first months after injury, a fibrocartilaginous primary callus forms. The dead bone is resorbed, and spongy bone appears. The size of the callus is affected by the immobility of the fracture site; the smaller the movement, the smaller the callus.
  • Replacement with lamellar bone: Spongy bone is gradually replaced by lamellar bone, uniting the fracture with a bony secondary callus.
  • Remodeling: The final phase restores the shape of the bone to normal and can take several years.

Factors Affecting Bone Healing

• Factors that can delay bone healing include:
  • Infection
  • Tissue fragments between the ends of the bone
  • Deficient blood supply
  • Old age
  • Medications such as steroids
• Factors that can improve bone healing include:
  • Limited movement/resting of the broken bone
  • Pain relief
  • Good nutrition
  • Appropriate movements under guidance
  • Younger age

Bone Conditions

• Common bone conditions include:
  • Fractures: Broken bones of various types.
  • Osteoporosis: Loss of bone density and strength.
  • Osteomyelitis: Infection of the bone.
  • Bone cancer: Primary bone cancers include osteosarcomas and chondrosarcomas, but most cancers found in bone spread from other organs.
  • Osteitis: Bone inflammation, e.g., Paget's disease of the bone.
  • Acromegaly: Overgrowth of bones in the face, hands, and feet.
  • Fibrous dysplasia: Abnormal growth or swelling of bone.
  • Rickets: Growing bones fail to develop due to a lack of vitamin D.
  • Multiple myeloma: Cancer of the plasma cells in bone marrow.