Terminology:

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Basics of Bone and Cartilage Healing and
Transplantation
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Terminology

• Bone is a dynamic biological tissue composed of
  metabolically active cells that are integrated
  into a rigid framework.
• Graft
• Vascularized bone graft
• Autograft
• Isograft
• Homograft (allograft)
• Heterograft (xenograft)
• Composite graft
• Implants
• Bone conduction, induction, integration

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Types of bone

• Histological
• Immature (Woven, Bundle)
• Mature (compact, cancellous)
• Anatomical
• Flat (skull, scapula, )
• Long (femur, tibia, )
• Sesamoid (patella)
• Healing
• Membranous (enchondral) ? cranial vault, facial
  bone,
• Endochondral ? skull base, long bones, ribs
• Dual mechanism ? mandible, sphenoid, occipital
  bones

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Endochondral Ossification

• Within cartilage. Interstitial growth. Cells
  swell, burst, replace by osteocytes with Ca

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Endochondral Ossification

• Secondary ossification - epiphysis
• Articular cartilage and epiphysial plate -

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Membranous Ossification

• Skull, mandible, clavicle.
• Fibrous membrane, Os. center, trabeculae

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Bone Structure
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• 65 inorganic (Ca)
• 35 organic
• (34 collagen, ..)
• (1 cells)

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Bone cells
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Osteocytes

• Derived from
• Mesenchymal precursor cells
• stem cells in bone marrow
• osteoprogenitor cells of periosteum

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Osteoclasts

• Derived from
• Hematopoetic stem cells in bone marrow (GM-CFU)
  that undergo endoreduplication
• old theory fusion of monocytes

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Remodeling

• Wolffs law
• -bone formed in response to mechanical load
• dynamization/staged destabilization-increased
  load can lead to increased bone formation
• -lamellar bone and marrow cavity form

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Type of Fracture Healing

• Direct Healing
• Primary Osteonal Reconstruction
• Contact healing
• Gap healing
• Secondary Osteonal Reconstruction
• Indirect Healing
• Distraction Osteogenesis

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Indirect Bone Healing

• Stages
• 1) the inflammatory stage (hematoma)
• 2) the repair stage (soft ? hard callus)
• 3) the late remodeling stage.
• Types
• Rigid
• Semi-rigid
• Non-fusion

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Indirect Bone Healing(continue)

• Factors affecting healing
• I) General
• II) Local
• Complications
• Malunion arthritis.
• Delayed union.
• Non union.
• Joint involvement - ankylosis
• Bone necrosis nutrient artery
• Pseudoarthrosis

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Indications of bone graft

• Nonunion fractures
• Highly comminuted fractures
• Fractures with bone loss
• When expecting a delayed union
• Augmentation and normalization of facial contour
• Creation of congenitally missing parts of skeleton

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Why we do bone graft?

• Osteognesis
• viable cells contribute to new bone formation
• Osteoinduction
• proteins, factors, hormones are transferred that
  modulate host cells
• Osteoconduction
• matrix upon which new bone can be formed
• implants can be osteoconductive

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Types of autogenous graft

• Cancellous bone
• metaphyseal regions, increase surface area, 80
  porosity
• Cortical bone
• Increase mechanical strength, 10 porosity
• frequently corticocancellous
• Osteochondral
• cartilage attached to parent bone
• Composite
• fresh graft added to preserved allograft
• Vascularized grafts
• Vascularized corticocancellous grafts

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Sources of autogenous grafts

• Iliac creast
• Rib
• Calverial bone
• Scapula
• Radius
• Vascularized fibula
• Vascularized rib
• medial aspect of tibial diaphysis

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Healing of autograft

• Inflammation
• Revascularization
• 2x time for Cancellous grafts due to porosity
• Osteoinduction
• decreased with cortical grafts
• Osteoconduction
• decreased with cortical grafts
• Remodeling
• initiated with osteoclasts (vs. osteoblasts) with
  cortical grafts

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Healing of allograft

• Creeping substitution
• Basic bone remodeling at graft-host interface
• bone resorption is followed by bone production
• May take years

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Bone Graft Substitute (BMP)

• Bone
• Morphogenetic
• Protein
• Only known extracellular protein known to be able
  to initiate new bone formation

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BONE and CARTILAGE

• Bone (osteo)
• vascular
• mesodermal origin
• cells and matrix
• osteoblasts
• osteocytes
• osteoclasts
• periosteum
• collagen type 1
• appositional growth
• -----
• compact, cancellous, woven

• Cartilage (chondro)
• avascular - requires diffusion
• mesodermal origin
• cells and matrix
• chondroblasts
• chondrocytes
• -----
• perichondrium
• collagen types 1,2
• appositional growth
• interstitial growth
• hyaline, elastic, fibrocartilage
• except articular cartilage

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