Bone Function Structure Mr Lee Van Rensburg Mr Staton Phillips 2015

Function 1Mechanical Role 2Ionic Reservoir 3Haemopoietic Marrow

Structure 10%Cells (functional) 90%Matrix (structural)

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

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

Resorb bone by forming: Howships lacunae

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

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

Osteoblasts Form bone Undifferentiated mesenchymal cells Line bone surfaces

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

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

Osteocytes 90% of Cells Osteoblasts trapped in matrix

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

Structure 10%Cells Osteoclasts Osteoblasts Osteocytes90% Bone Lining cells 90%Matrix

Structure 10%Cells Osteoclasts Osteoblasts Osteocytes90% Bone Lining cells 90%Matrix

Structure 10%Cells Osteoclasts Osteoblasts Osteocytes90% Bone Lining cells 90%Matrix 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

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

Tensile strength

Compressive strength

Microscopic Primary Immature Woven Secondary Mature Lamellar

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

Microscopic Primary Immature Woven Secondary Mature Lamellar

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 Primary Immature Woven 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

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

Questions ?

Biomechanics