Bone
Function
Structure
Mr Lee Van Rensburg
Mr Staton Phillips
2014

1
2
Mechanical Role
Ionic Reservoir
3 Haemopoietic Marrow
Function

10%
Cells
(functional)
(structural)
Structure

10%
90%
Structure
Cells
Osteoclasts
Osteoblasts
Osteocytes
Bone Lining cells
Matrix

Osteoclasts
Multinucleated giant cells
Haemopoetic origin (monocyte progenitors)
Resorb bone

Osteoclasts
Resorb bone by forming:
Howships lacunae

Osteoclasts
Integrins – attach to bone sealing space
Produce H + via carbonic anhydrase
Lower PH increases solubility of
Hydroxyapatite
Organic matrix resorbed by proteolysis

10%
90%
Structure
Cells
Osteoclasts
Osteoblasts
Osteocytes
Bone Lining cells
Matrix

Osteoblasts
Form bone
Undifferentiated mesenchymal cells
Line bone surfaces

Osteoblasts affected by:
IL
PDGF
IDGF
PTH
1,25 Dihydroxy vitamin D
Glucocorticoids
Prostaglandins
Oestrogen
Osteoblasts

10%
90%
Structure
Cells
Osteoclasts
Osteoblasts
Osteocytes
Bone Lining cells
Matrix

Osteocytes
90% of Cells
Osteoblasts trapped in matrix

Osteocytes
Maintain bone
Control Extracellular Ca and P
Stimulated by Calcitonin
Inhibited by PTH

10%
90%
Structure
Cells
Osteoclasts
Osteoblasts
Osteocytes 90%
Bone Lining cells
Matrix

10%
90%
Structure
Cells
Osteoclasts
Osteoblasts
Osteocytes 90%
Bone Lining cells
Matrix

10%
Structure
Cells
Osteoclasts
Osteoblasts
Osteocytes 90%
Bone Lining cells
Organic 40%
Inorganic 60%

Organic (40%)
Collagen (90%)
Proteoglycans
Non collagenous matrix proteins
Glycoproteins
Phospholipids
Phosphoproteins
Growth factors
Cytokines

Organic (40%)
Collagen (90%)
Type - B
ONE
Polypeptide triple helix
Tropocolagen bond together
Forming fibrils

Inorganic (60%)
Most Hydroxyapatite
Ca
10
(PO
4
)
6
(OH)
2
Fills in holes in Collagen

Tensile strength

Compressive strength

Primary
Immature
Woven
Microscopic
Secondary
Mature
Lamellar

Woven Bone
LOCATION
PROPERTIES
Embryonic Skeleton
Neonatal Skeleton
Growing Metaphysis in under 4 yr olds
ISOTROPIC uniform physical properties in all directions
SOFT
FLEXIBLE
Near sutures of skull
In tooth sockets
Some Tendon insertions
RAPID DEPOSITION/TURNOVER
Callus
HIGH No. OF CELLS

Primary
Immature
Woven
Microscopic
Secondary
Mature
Lamellar

Lamellar Bone
LOCATION
PROPERTIES
ANISOTROPIC
Properties differ based on the direction that is measured
HARD
Throughout the adult skeleton
RIGID
SLOW DEPOSITION/TURNOVER
LOW No. OF CELLS

Primary
Immature
Woven
Macroscopic
Secondary
Mature
Lamellar

Cortical Bone
Compact
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 Bone trabecular
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

Bone circulation
Receives 5-10% of CO
Three sources
1. Endosteal (nutrient artery)
2. Metaphyseal epiphyseal system
3. Periosteal system
McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation
1. Nutrient artery
Enters diaphysis to medullary cavity
Ascending and descending arterioles
Centrifugal high pressure
Inner 2/3rds of cortex
McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation
2. 2. Metaphyseal epiphyseal system
Periarticular vascular plexus eg. geniculate arteries
McCarthy I. J Bone Joint Surg 2006:88:4-9

Bone circulation
3. Periosteal system low pressure on periosteum
Outer 1/3 rd of cortex
McCarthy I. J Bone Joint Surg 2006:88:4-9

Biomechanics