Terminology: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

Types of bone: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

Endochondral Ossification:Endochondral Ossification:

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

Endochondral Ossification:Endochondral Ossification:

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

Membranous Ossification:Membranous Ossification:

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

Bone StructureBone Structure

•65% inorganic (Ca)•35% organic (34% collagen, ..)

(1% cells)

Bone cellsBone cells

OsteocytesOsteocytes

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

OsteoclastsOsteoclasts

• Derived from:– Hematopoetic stem cells in bone marrow (GM-CFU) that

undergo endoreduplication – old theory = fusion of monocytes

RemodelingRemodeling

• Wolff’s 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

Type of Fracture HealingType of Fracture Healing

• Direct Healing– Primary Osteonal Reconstruction• Contact healing• Gap healing

– Secondary Osteonal Reconstruction

• Indirect Healing

• Distraction Osteogenesis

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

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

Indications of bone graftIndications 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

Why we do bone graft?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

Types of autogenous graftTypes 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

Sources of autogenous graftsSources of autogenous grafts

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

Healing of autograft: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

Healing of allograft:Healing of allograft:

• “Creeping substitution”

• Basic bone remodeling at graft-host interface– bone resorption is followed by bone

production

• May take years

Bone Graft Substitute (BMP)Bone Graft Substitute (BMP)

Bone

Morphogenetic Protein

Only known extracellular protein known to be able to initiate new bone formation

BONE and CARTILAGEBONE 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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