Metabolic Bone Metabolic Bone DiseasesDiseases

BYBYDr. Abdullah H .A . Juma , FRCS Dr. Abdullah H .A . Juma , FRCS

EdEdAssociate Professor & Associate Professor &

Consultant Orthopaedic Consultant Orthopaedic SurgeonSurgeon

IntroductionIntroduction

Metabolic bone 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 .

Bone characteristics

1. Bone Morphology .

2. Bone Functions .

1. Bone Morphology 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 .

Bone Morphology

1. Organic matrix .2. Bone cells .3. Bone mineral .4. Blood vessels .5. Bone marrow .

1. Organic Matrix

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 .

Collagen stability decreases with Collagen stability decreases with age.age.

4 types of collagen . Type I only 4 types of collagen . Type I only occurs in bone with low occurs in bone with low carbohydrate & < 10 hydroxylysine carbohydrate & < 10 hydroxylysine residues per alpha chain .residues per alpha chain .

Non-collagenous is protein linked to Non-collagenous is protein linked to substances forming proteoglycans substances forming proteoglycans & glycoproteins or exist as an & glycoproteins or exist as an isolated material such as Albumin & isolated material such as Albumin & Alpha Alpha –– Carboxyglutamic acid . Carboxyglutamic acid .

Proteoglycans consist of a 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 .

Bone Morphology

1. Organic matrix .2. Bone cells .3. Bone mineral .4. Blood vessels .5. Bone marrow .

22 . .Bone cells

Control formation , composition & resorption of bone .

Types of cells : . Osteoblasts . . Osteoclasts . . Osteocytes . . Fibroblasts . . Myeloproliferative cells .

Osteoblasts Bone forming cells , 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 .

22 . .Bone cells

Types of cells :

. Osteoblasts . . Osteoclasts . . Osteocytes . . Fibroblasts . . Myeloproliferative cells .

Osteoclasts

Metabolic bone diseases are Metabolic bone diseases are caused by an imbalance in the caused by an imbalance in the

metabolism of bone resorption & metabolism of bone resorption & deposition due todeposition due to: :

1.1. Defect of Mineralization .Defect of Mineralization .

2.2. Defect of bone matrix .Defect of bone matrix .

3.3. Excessive bone resorption .Excessive bone resorption .

4.4. PagetPaget’’s disease .s disease .

1.1. Defect of Mineralization .Defect of Mineralization .

2.2. Defect of bone matrix .Defect of bone matrix .

3.3. Excessive bone resorption .Excessive bone resorption .

4.4. PagetPaget’’s disease .s disease .