Structural and Congenital Defects

• Bone Cells

  • Osteogenic Cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteogenic Cells

  Undifferentiated cells that develop into osteoblasts
• Osteoblasts


  • Deposit bone matrix
  • Responsible for bone formation, forming new bones and growing/healing existing ones
• Osteocytes


  Mature bone cells trapped in the calcified matrix (osteoid) that maintain bone tissue
• Osteoclasts


  • From a different cell lineage (monocytes and macrophages)
  • Responsible for bone resorption
• Normal Bone Structures

  • Growth Plate
  • Trabecular Bone
  • Cortical Bone
  • Diaphysis
• Growth Plate

  Also known as epiphyseal plate, responsible for the growth in length of the bone
• Trabecular Bone

  Also known as cancellous bone, has a red appearance due to active bone marrow
• Cortical Bone

  Also known as compact bone, has a much higher density than trabecular bone
• Diaphysis


  Space filled with bone marrow
• Types of Ossification

  • Endochondral Ossification
  • Intramembranous Ossification
• Endochondral Ossification


  Bone forms by replacing hyaline cartilage, e.g. in long bones
• Intramembranous Ossification

  Bone forms directly from mesenchymal tissue, e.g. flat bones of the cranium
• Types of Bone Growth

  • Interstitial Growth
  • Appositional Growth
• Interstitial Growth


  Growth by adding within the interior of a structure, occurs at the epiphyseal plate
• Appositional Growth


  Growth by adding to the free surface of bone, can occur at endosteum or periosteum
• Epiphyseal Plate

  Junction between epiphysis and diaphysis of growing long bone, contains hyaline cartilage being replaced by bone, site of long bone elongation
• Epiphyseal Line


  Completely ossified remnant of the epiphyseal plate
• Ossification


  Also known as osteogenesis, bone formation
• Ossification Center


  Cluster of osteoblasts found in the early stages of intramembranous ossification
• Osteoid

  Uncalcified bone matrix secreted by osteoblasts, contains collagen and collagen precursors
• Perichondrium

  Covering of cartilage
• Proliferative Zone


  Region of the epiphyseal plate that makes new chondrocytes to replace those that die at the diaphyseal end, contributing to longitudinal growth
• Remodeling

  Process by which osteoclasts resorb old or damaged bone, and osteoblasts form new bone to replace that which is resorbed
• Reserve Zone


  Region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis
• Zone of maturation and hypertrophy

  Region of the epiphyseal plate where chondrocytes from the proliferative zone grow and mature, contributing to longitudinal growth
• Chondrodysplasia


  Also known as disproportionate dwarfism, endochondral growth (length) is absent but appositional growth (width) is normal
• Chondrodysplasia in bovine

  • Also referred to as bull dog calves
• Chondrodysplasia in Alaskan Malamute

  • Also suffer with anemia
• Osteopetrosis

  Increased density of trabecular bone with the reduction of medullary cavity, due to a genetic defect of osteoclasts
• Osteopetrosis in bovine


  • Rarely seen in dogs and cats
• Porcine Hyperostosis


  Genetic disease of pigs characterized by the abnormal deposition of bone along the periosteal surface of long bones, causing swelling of the forelegs
• Micromelia


  Abnormally short and poorly developed forelegs
• Phocomelia


  Short and poorly developed forelegs, with the humerus and radius missing and the carpal and digits appearing like flippers
• Paromelia

  Distal portion of the limb is missing
• Syndactylia


  Fusion of digits, a common genetic malformation in pigs, also occurs in cattle and sheep
• Polydactylia


  Increase in the number of digits, which occurs practically in all domestic species
• Scoliosis

  Lateral deviation of the vertebrae, due to complex embryological development
• Lordosis


  Ventral deviation of the vertebrae
• Kyphosis

  Dorsal deviation of the vertebrae