BoneFunctionStructure

Mr Lee Van Rensburg

Mr Staton Phillips

2014

Function

1 Mechanical Role

2 Ionic Reservoir

3 Haemopoietic Marrow

Structure

10% Cells(functional)

90% Matrix(structural)

Structure

10% CellsOsteoclastsOsteoblastsOsteocytesBone Lining cells

90% Matrix

Multinucleated giant cellsHaemopoetic origin (monocyte progenitors)Resorb bone

Osteoclasts

Osteoclasts

Resorb bone by forming:Howships lacunae

Integrins – attach to bone sealing spaceProduce H+ via carbonic anhydraseLower PH increases solubility of Hydroxyapatite Organic matrix resorbed by proteolysis

Osteoclasts

Structure

10% CellsOsteoclastsOsteoblastsOsteocytesBone Lining cells

90% Matrix

Osteoblasts

Form boneUndifferentiated mesenchymal cellsLine bone surfaces

Osteoblasts

Osteoblasts affected by:

ILPDGFIDGFPTH1,25 Dihydroxy vitamin DGlucocorticoidsProstaglandinsOestrogen

Structure

10% CellsOsteoclastsOsteoblastsOsteocytesBone Lining cells

90% Matrix

Osteocytes

90% of CellsOsteoblasts trapped in matrix

Maintain boneControl Extracellular Ca and PStimulated by CalcitoninInhibited by PTH

Osteocytes

Structure

10% CellsOsteoclastsOsteoblastsOsteocytes 90%Bone Lining cells

90% Matrix

Structure

10% CellsOsteoclastsOsteoblastsOsteocytes 90%Bone Lining cells

90% Matrix

Structure

10% CellsOsteoclastsOsteoblastsOsteocytes 90%Bone Lining cells

90% MatrixOrganic 40%Inorganic 60%

Organic (40%)

Collagen (90%)ProteoglycansNon collagenous matrix proteins

GlycoproteinsPhospholipidsPhosphoproteins

Growth factorsCytokines

Organic (40%)Collagen (90%)

Type - BONEPolypeptide triple helix Tropocolagen bond togetherForming fibrils

Most Hydroxyapatite

Fills in holes in Collagen

Inorganic (60%)

Ca10 (PO4)6 (OH)2

Tensile strength

Compressive strength

Microscopic

PrimaryImmatureWoven

SecondaryMatureLamellar

Woven Bone

LOCATION

Embryonic SkeletonNeonatal Skeleton Growing Metaphysis in under 4 yr olds

Near sutures of skullIn tooth socketsSome Tendon insertions

Callus

PROPERTIES

ISOTROPIC

SOFT

FLEXIBLE

RAPID DEPOSITION/TURNOVER

HIGH No. OF CELLS

uniform physical properties in all directions

Microscopic

PrimaryImmatureWoven

SecondaryMatureLamellar

Lamellar Bone

LOCATION

Throughout the adult skeleton

PROPERTIES

ANISOTROPIC

HARD

RIGID

SLOW DEPOSITION/TURNOVER

LOW No. OF CELLS

Properties differ based on the direction that is measured

Macroscopic

PrimaryImmatureWoven

SecondaryMatureLamellar

Cortical BoneCompact

80% of the adult skeleton

20 times stiffer than cancellous bone

Lamellae in concentric rings aligned with lines of force

Complex arrangement of canals serving the lamellae(Haversian System)

Cancellous Bonetrabecular

20% of the adult skeleton

20 times less stiff than cortical bone

Lamellae also present aligned with lines of force

No Haversian System

Bone circulation

McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation

Receives 5-10% of CO

Three sources1.Endosteal (nutrient artery)2.Metaphyseal epiphyseal system3.Periosteal system

McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation

1. Nutrient arteryEnters diaphysis to medullary cavityAscending and descending arteriolesCentrifugal high pressureInner 2/3rds of cortex

McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation

2. 2. Metaphyseal epiphyseal systemPeriarticular vascular plexus

eg. geniculate arteries

McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation

3. Periosteal systemlow pressure on periosteum Outer 1/3rd of cortex

Questions ?

Biomechanics