Bones and its classification

• Bone is a living structure composed of highly vascularized & mineralized connective tissue.
• Functions of bone

  1. Provides a bony framework to give form & support.
  2. Provides a lever for movements in locomotion
  3. Provides areas for attachment of muscle & ligaments
  4. Protection of viscera (e.g. skull, ribs)
  5. Production of blood cells by marrow.
  6. Storage of calcium & phosphate ions.
  7. Transmission of weight & force.
• Total number of bones in the body

  • 206 of which 126 are in appendicular skeleton & the rest in axial skeleton.
• Single bones - 33 ( 26 vertebra, sternum, occipital, sphenoid, frontal, mandible, vomer and hyoid); the rest are paired.
• Bones of the males are usually larger & heavier than females.
• Bones are useful for the assessment of sex, age, skeletal maturity, to diagnose nutritional and endocrine disorders.
• Human bones can be differentiated from animal bones.
• Classification of Bones

  According todevelopment

  1. Membranous bone – skull bones
  2. Endochondral bone – limb bones
• Classification of Bones

  According to region

  1. Axial bone – skull, vertebra, ribs
  2. Appendicular bone – bones of limb & girdles
• Classification of Bones

  According to structure

  1. Spongy bone – ends of long bones & short bones.
  2. Compact bone – shaft of long bones
• Fill in the blank

  A) shaft (diaphysis)

  B) epiphyses

  C) haversian

  D) meshwork

  E) Yellow

  F) Red

  G) red

  
• Classification of Bones

  According to shape

  1. Long bone
  2. Short bone
  3. Flat bone
  4. Irregular bone
  5. Sesamoid bone
  6. Pneumatic bone
  7. Heterotopic bone
  8. Accessory bone

  
• Long bone

  • Location: Confined to limbs.
  • Formation: Develop in cartilage (except clavicle).
  • Shape: Longer in length (shaft) than in breadth and thickness (ends).
  • Ends: Have two ends - articular (participates in joint formation), covered with hyaline cartilage.
  • Shaft: Typically cylindrical.
  • Marrow Cavity: Contains a marrow cavity filled with red marrow (in children) or yellow marrow (in adults).
• Short bone

  1. Length, breadth & thickness are approximately equal
  2. Cubical in shape with 6 surfaces : 4 are articular and the other two is free for attachment of ligaments & for the entry of blood vessels.
  3. They develop in cartilage.
• Flat bone

  • Resemble sandwiches; consists of 2 layers of compact bone with spongy bone & marrow between them.
  • Some flat bones are so thin that there is no intervening spongy bone.
  • Most bones of the skull, sternum, scapula, ribs are examples.
• Irregular bone

  • They are irregular or mixed shape & do not fit into the above types.
  • They are spongy bones covered by a thin layer of compact bone.
  • All skull bones (except flat bones) are irregular – sphenoid, temporal, maxilla; vertebra & hip bone
• Sesamoid bone

  • are nodules of bone found embedded in certain tendons at places where they are exposed to severe pressure or friction.
  • Example – patella
• Functions of the sesamoid bones are

  • to resist pressure
  • to minimize friction
  • to alter the direction of pull of the muscle
  • to maintain the local circulation.
• Characteristics of Sesamoid Bones

  • Develop in the tendons of the muscles.
  • Are devoid of periosteum.
  • Ossify after birth usually by multiple centers.
  • Lack haversian system.
• Patella is the largest sesamoid bone in the body and the

  cartilage covering, its articular surface is the thickest

  articular cartilage in the body.
• Sesamoid bones are not classified as true bones as they

  are not covered by periosteum.
• Accessory bone

  • Not regularly present.
  • Example – supernumerary digits, sutural or wormian bones.
• Metopic suture in frontal bone

  • is persistence of a suture between the right & left halves of the frontal bone after 6 years of age.
  • Usually found in primitive races. This suture may be mistaken for fracture
• Pneumatic bone

  • are skull bones with air cavities
  • Example – ethmoid, maxillary & sphenoid bones
• Heterotopic bone

  • are bone pieces found in places other than its normal sites such as scars or calcified tendons.
• Each long bone has a shaft (diaphysis) and two ends (epiphyses).
• At birth both ends of long bone are cartilaginous – "cartilaginous epiphyses". The part of the bone between the two ends is the diaphysis.
• Diaphysis is a thick walled tube composed of compact bone which surrounds a central marrow cavity containing red or yellow marrow.
• The diaphysis is compact bone and is covered by periosteum. It is the site of primary ossification
• Metaphysis

  • is the part of the diaphysis adjacent to the epiphyseal plate.
  • is highly vascular.
  • is the area of greatest growth activity in the long bone and the weakest point in the bone.
• The layer of hyaline cartilage between the diaphysis & epiphysis is called the epiphyseal plate.
• Epiphyseal plate is the site of bone growth.
• When growth stops the diaphysis fuses with the epiphysis and the cartilaginous epiphyseal plate changes into bone when growth ceases.
• Fill in the blank

  A) Epiphysis

  B) Epiphyseal plate

  C) Diaphysis

  D) Metaphysis

  
• Epiphysis

  • is usually wider than the shaft
  • is the site of secondary ossification.
  • is composed of spongy bone covered by a thin layer of compact bone.
• The surface of the epiphysis which articulate with a neighboring bone is called articular surface and is always covered by hyaline cartilage
• There are 4 types of epiphysis: pressure, traction, atavistic, and aberrant.
• Pressure epiphysis is articular and takes part in transmission of the weight, for example, the head of femur.
• Traction epiphysis is non-articular and does not take part in the transmission of the weight, it ossifies later than the pressure epiphyses, examples include trochanters of femur and tubercles of humerus.
• Atavistic epiphysis is phylogenetically an independent bone which in man becomes fused to another bone, for example, the coracoid process of scapula.