Metabolic Bone Diseases

Metabolic Bone Diseases

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  Metabolic Bone DiseasesBY Dr. Abdullah H .A . Juma , FRCS Ed Associate Professor & Consultant Orthopaedic Surgeon
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  Introduction Metabolic bone diseases describes a group of disorders due to abnormalities of formation ( bone morphology ) and metabolism of bone ( functions ) . Bone : An active tissue undergoing continuous structural & metabolic changes . The bone is surrounded by a bone fluid different from the whole body extracellular fluid .
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  Bone characteristics BoneMorphology . Bone Functions .
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  1. BoneMorphology Morphologically , bone can be mature (lamellar ) or immature ( woven ) or unmineralized ( osteoid ) . 2 types of bone in mature skeleton : . . Compact cortical bone . Consists of 50% Haversian systems (osteons) & 50% interstitial bone . Osteons consist of rings of osteocytes around central canal which carries blood & lymph vessels . The cortical bone surrounds marrow cavities & form shafts of long bones . . . Cancellous bone . Anastomosing trabeculae within cortical bone and predominantly seen in vertebrae ,flat bones & ends of long bones .
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  Bone Morphology Organic matrix . Bone cells . Bone mineral . Blood vessels . Bone marrow .
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  1. OrganicMatrix It’s the frame work of bone . 2 types : collagenous ( 90% ) and non– collagenous ( 10% ) . Collagen is triple helix consist of 3 polypeptide alpha chains . Each chain has 1000 amino acids & synthesized within the fibroblasts or osteoblasts and is broken down by collagenases to hydroxyproline & hydroxylysine and excreted in urine .
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  Collagen stability decreaseswith age. 4 types of collagen . Type I only occurs in bone with low carbohydrate & < 10 hydroxylysine residues per alpha chain . Non-collagenous is protein linked to substances forming proteoglycans & glycoproteins or exist as an isolated material such as Albumin & Alpha – Carboxyglutamic acid .
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  Proteoglycans consist ofa protein core linked to carbohydrate units such as mucopolysaccharides . Glycoproteins .. 2 forms exist in the bone : . Sialoprotein . A high metal-binding capacity . . Alpha 2 heat-stable glycoprotein . Synthesized in liver .
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  Bone Morphology Organic matrix . Bone cells . Bone mineral . Blood vessels . Bone marrow .
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  2. Bonecells Control formation , composition & resorption of bone . Types of cells : . Osteoblasts . . Osteoclasts . . Osteocytes . . Fibroblasts . . Myeloproliferative cells .
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  Osteoblasts Bone formingcells , synthesizing collagen , non-collagen & mineralization of bone . Uniform in size . Mononuclear & basophilic cytoplasm. Lie in single layers close to the osteoid tissue of newly formed bone. High content of Alkaline Phosphatase . Have fine processes which extend into the osteoid tissues . If resting , appear spindle & flat . If active , appear larger & plump .
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  2. Bonecells Types of cells : . Osteoblasts . . Osteoclasts . . Osteocytes . . Fibroblasts . . Myeloproliferative cells .
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  Osteoclasts
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  Metabolic bone diseasesare caused by an imbalance in the metabolism of bone resorption & deposition due to : Defect of Mineralization . Defect of bone matrix . Excessive bone resorption . Paget’s disease .
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  Defect of Mineralization. Defect of bone matrix . Excessive bone resorption . Paget’s disease .
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  1. Defect ofmineralization