Peggers Super Summaries Basic Sciences Bone

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1 Bone Overview & Turnover BONES Function o Support o Protection o Assisting movement o Storage of minerals o Production of red blood cells from marrow Types o Cancellous o Compact with Haversian systems COMPOSITION Contains o 60% inorganic hydroxyapatite o 40% organic collage Turnover o Calcium - increased by parathyroid hormone, increased release by Vit D, decreased by calcitonin (turns off osteoclasts) o PO4 increases excretion by PTH Bone healing: STAGES Haematoma immediately to day 7 o Clotting cascade and proteins o Complement C3/5 o Neutrophils o Angiogenesis o Cytokines defined as proteins used in cell movement Soft callus week 1-4 ANGIOGENESIS o Type 2 collagen o Fibrin o Fibroblasts 100% strain environment o Chondrocytes 10% strain environment Hard callus weeks 4-12 o Type 1 collagen and less strain 2% Remodelling >3/12 LEVELS Mechanical level Perren strain theory o Strain = change in length / original length

2 o 100% strain granulation tissue o 10% strain - cartilage o 2% strain - bone Biological level o Oxygen o Growth factors Transforming GF beta differentiation of stem cells Platelet GT IL1 Vascular endothelial GF angiogenesis, chemotactic BMPs BMP2 mitogenic BMP7 - angiogenic o ph alkaline phosphatase Bone Basics: DEFINITION Ossified connective tissue made up of organic and non-organic bone matrix OVERVIEW Immature and mature forms of bone 5 cell types Inorganic and organic bone matrix 5-10% of CO Strength proportional to 4 th power of radius MECHANICAL PROPERTIES Anisotropic different mechanical properties depending on direction Viscoeleasticity mechanical properties change depending on velocity of force Rate dependant o Stress relaxation decrease stress over time with constant strain o Creep change in strain under constant stress o Hysteresis energy on loading and unloading is not equal

3 FUNCTION Calcium reservoir Mechanical Haematopoietic Protecting organs MATRIX 60% inorganic provides compressive strength o Hydroxyapatite Ca10(PO4)6(OH)2 [10/6/2] o Calcium phosphate o Osteocalcin o Osteonectin o Osteopontin 40% organic o 90% type 1 collagen (bone = one = type 1 collagen) o Growth factors / BMPs / prostaglandins etc BONE CLASSES Flat haemopoietis in adults Long haemopoeisis in children Irregular Strut Sesamoid BONE TYPES New bone or callus immature o Woven and irregular o Isotropic Mature bone o Lamellar o Anisotropic o Consists of Cortical bone Concentric rings of haversian systems Horizontal canals volkmann s Youngs modulus 20GPa

4 Cancellous Interconnecting trabeculae Youngs modulus 1GPa Periosteum CELLS Osteoblasts (from undifferentiated mesenchymal stem cells) makes type 1 collagen Osteocytes trapped osteoblasts regulate calcium Osteoclasts from macrophage leaves cutting cones or Howships lacunae has brush boarder and multiple nuclei o Failure causes osteopetrosis o Over activity causes paget s Bone lining cells inactive osteoblasts Bone remodelling units BLOOD SUPPLY Nutrient artery o Medullary system high pressure o Running via volkmann s canals Periarticular system o Metyaphyseal and epiphyseal capsule Periosteum o Outer 1/3 of cortex o Low pressure system

5 BONE FORMATION Peggers Super Summaries Basic Sciences Bone Endochondral growth from growth plates in long bones Intra-membranous growth found in flat bones i.e. skull, clavicle GROWTH PLATE 4 layers RPHO 1. Resting 2. Proliferating 3. Hypertrophic 4. ossification BONE REMODELLING cortical o cutting cones cancellous o woven o lamella WHAT CONTROLS BONE REMODELLING mechanical Woolfe s law chemical Electrical pizoelectric from charged cells BONE METABOLISM Vitamin D o Converted from light in the skin o Increases production or retension of calcium in SI Increases osteoclastic activity PTH o From parathyroid gland o Increases production or retension of calcium in kidney Calcitonin o From thyroid (parafollicular C cells) o Decreases calcium by turning off osteoclasts Oestrogen o Inhibits bone formation and resorption

6 Steroids o Decreases calcium and bone matrix formation Bone Injury Healing OVERVIEW Energy = ½ mv 2 Strain of cortical bone is 2% (anisotropic) Strain of cancellous bone is 75% Bone is viscoeleastic HEALING o Requires strain <2% and absolute stability to allow cutting cones across fracture site o Strain 2-10% o Relative stability and heals with callus STAGES OF CALLUS Haematoma and inflammation o Fibrin clot and inflammatory cells (BMPs, IL 1&6, TGF-B) Soft callus o Angiogenesis o Intramembranous and enchondral (bridging external callus) Hard callus o Fibrous tissue replaced by osteoid which is mineralised Remodelling o Woven bone into lamella NON UNION Types of non-union o Hypertrophic Poor biomechanical stability o Atrophic Poor biomechanical and biological activity

7 Perren s strain theory o Granulation tissue 100% strain o Fibrous tissue 17% o Fibrocartilage 2-10% o Lamella bone 2% Factors affecting healing Cierny classification host and physiology most 7mportant o Local Trauma n/v injury reduction bone loss infection o systemic smoking diabetes nutrition drugs ibuprofen steroids Bone Grafting INDICATIONS FOR BONE GRAFTING provide stability stimulate new bone enhance fracture healing TYPES OF BONE GRAFT autograft from host o vascularised o non-vascularised Allograft ie graft jacket Xenograft Bone graft substitiute o Calcium, hydroxyapatite, ceramic or silicon based Augments o BNP or electromagnetic of US fields PROPERTIES OF BONE GRAFT

8 Osteogenicity presence of living cells Osteoconduciton 3D scaffold Osteoinduction differentiation of mesenchymal stem cells