Bone Dystrophy PDF

Bone osteodystrophy Prepared by: Rasha Arafa Abd El-maksoud  LONG BONES Compact Bone – dense outer layer Spongy Bone – (cancellous bone) honeycomb of trabeculae (needle-like or flat pieces) filled with bone marrow  COMPACT BONE: (OSTEON) EXTERNAL LAYER - called lamellar bone...

Bone osteodystrophy Prepared by: Rasha Arafa Abd El-maksoud  LONG BONES Compact Bone – dense outer layer Spongy Bone – (cancellous bone) honeycomb of trabeculae (needle-like or flat pieces) filled with bone marrow  COMPACT BONE: (OSTEON) EXTERNAL LAYER - called lamellar bone (groups of elongated tubules called lamella) - majority of all long bones - protection and strength (wt. bearing) - concentric ring structure - blood vessels and nerves penetrate periosteum through horizontal openings called perforating (Volkmann’s) canals.  COMPACT BONE: (OSTEON) EXTERNAL LAYER Central (Haversian) canals run longitudinally. Blood vessels and nerves. - around canals are concentric lamella - osteocytes occupy lacunae which are between the lamella - radiating from the lacunea are channels called canaliculi (finger like processes of osteocytes) COMPACT BONE - Lacunae are connected to one another by canaliculi - Osteon contains: - central canal - surrounding lamellae - lacunae - osteocytes - canaliculi SPONGY BONE (CANCELLOUS BONE): INTERNAL LAYER - trabecular bone tissue (haphazard arrangement). - filled with red and yellow bone marrow - osteocytes get nutrients directly from circulating blood. - short, flat and irregular bone is made up of mostly spongy bone HISTOLOGY OF BONE Histology of bone tissue Cells are surrounded by matrix. Cells of Bone Tissue - 25% water - 25% protein - 50% mineral salts 4 cell types make up osseous tissue Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts  Osteoprogenitor cells: - derived from mesenchyme Cells of Bone Tissue - all connective tissue is derived - unspecialized stem cells - undergo mitosis and develop into osteoblasts - found on inner surface of periosteum and endosteum.  Osteoblasts: - bone forming cells - found on surface of bone (arrow) - no ability to mitotically divide - collagen secretors Osteocytes: - mature bone cells - derived form osteoblasts - do not secrete matrix material - cellular duties include exchange of nutrients and waste with blood.  Osteoclasts - bone resorbing cells - bone surface - growth, maintenance and bone repair Abundant inorganic mineral salts: - Tricalcium phosphate in crystalline form called hydroxyapatite Ca3(PO4)2(OH)2 - Calcium Carbonate: CaCO3 - Magnesium Hydroxide: Mg(OH)2 - Fluoride and Sulfate  SKELETAL CARTILAGE Chondrocytes: cartilage producing cells. Lacunae: small cavities where the chondrocytes are encased. Extracellular matrix: jelly like ground substance. Perichondrium: layer of dense irregular connective tissue that surrounds the cartilage. No blood vessels or nerves Types of Cartilage Hyaline cartilage – (glassy) Most abundant cartilage Provides support through flexibility Articular cartilages and costal cartilage, larynx, trachea, and nose Elastic cartilage – contains many elastic fibers Able to tolerate repeated bending Ear and epiglottis Fibrocartilage – resists strong compression and strong tension An intermediate between hyaline and elastic cartilage Intervertebral discs and pubic symphysis BONE FORMATION The process of bone formation is called ossification Bone formation occurs in four situations: 1) Formation of bone in an embryo 2) Growth of bones until adulthood 3) Remodeling of bone 4) Repair of fractures  Diseases of bone Osteodystrophies. Inflammatory (osteomyelitis): Acute and chronic. Neoplastic: Benign and malignant.  Osteodystrophies Def: It is disturbance of bone growth. Types of osteodystronhies: A.Congenital: Exostosis. B.Acquired: 1.Fibrous dysplasia. 2.Paget’s disease of bone. 3.Osteoporosis. 4.Radiation osteodystrophy 5.Renal osteodystrophy. 6.Endocrinal osteodystrophy. 7. Digital clubbing. 8.Vitamin D deficiency: Includes: Rickets in children & Osteomalacia in adults Exostosis (osteochondroma, ecchondroma): Def: Hamartomatous lesion composed of bone covered by cap of cartilage. Pathogenesis: It is herniation of a part of epiphyseal cartilage through a defect in the ring of Ranvier. Ring of Ranvier: This ring is a periosteal cuff of bone that normally surrounds the growth cartilaginous plate. Function of Ring of Ranvier: 1. It is important to the mechanical integrity of the epiphyseal growth plate. 2. It guides the growth of the epiphyseal cartilage towards the metaphysis. A defect through this ring results in herniation and separation of a fragment of the epiphyseal plate. Persistent growth of the herniated fragment and its subsequent endochondral ossification results in a cartilage capped subperiosteal bone projection. Exostosis GENERAL CONSIDERATION  Exostosis (osteochondroma, ecchondroma): N/E: Number: It may be solitary or multiple. The multiple form is called multiple osteochondromatosis which is transmitted as Mendelian dominant and is liable to be complicated by chondrosarcoma. The lesion is formed of bony prominence with bluish grey irregular cauliflower- like cartilaginous cap. M/E: Bone trabeculae covered by cartilaginous cap. Fibrous dysplasia: Def: It is an acquired disturbance of bone growth characterized by presence of disorganized mixture of fibrous and osseous elements N/E: It may be either polyostotic (in more than one bone) or monostotic (in one bone). Site: In the medulla. Color: Grayish white. Consistency: Gritty with cysts. M/E: Irregular bone trabeculae embedded in a loosely arranged fibrous stroma. The bony trabeculae are formed of woven bone that lack osteoblastic rimming. Complications: Deformities of bone and fractures.  Fibrous dysplasia: Combination of bland hypocellular fibrous tissue with small fragments of woven bone without visible rimming by osteoblasts The trabecule are common referred as Chinese characters or resembling “Cs”and “Os”. Also may be called Alphabet Soup. This arrangement may mimic the appearance of Paget’s diseases Trabeculae are not lined with osteoblasts. Paget’s disease of Bone: Def: Acquired disturbance of bone growth characterized by bone resorption and new bone formation. Pathogenesis: It passes by 3 stages: Pathophysiology: increased osteoclastic bone resorption is the primary cellular abnormality 1-cause is thought to be a slow virus infection (intra-nuclear nucleocapsid-like structure): paramyxovirus & respiratory syncytial virus 2-Genetics 3-inheritance N/E: It may be polyostotic or monostotic. Sites: Mainly in the axial bones as skull, vertebrae iliac bone proximal femur, tibia and humerous. lytic phase intense osteoclastic resorption mixed phase resorption and compensatory bone formation sclerotic phase osteoblastic bone formation predominates all three phases may co-exist in the same bone  Paget’s disease of Bone: Long bones: ▪ They are irregularly thickened: The bone is added by subperiosteal and subendosteal bone formation leading to irregular bone formation on both sides. ▪ The new bone encroaches upon the medullary cavity which becomes narrow. ▪ The outer surface is rough and the bone looses its smooth ivory-like surface. ▪ Forward bowing of legs due to replacement of the cortical lamellar bone by the new woven bone. Bones of skull and face: ▪ Early: o Localized areas of rarefaction giving an appearance called osteoporosis circumscripta ▪ At a later stage the bones become thickened resulting in: o The head acquires a triangular appearance. o Cranial nerve compression. o Increase size of facial bones, the jaws is grossly affected and deformed. Vertebrae: Lumber and sacral vertebrae are affected. ▪ Early: Osteolysis leading to kyphosis due to anterior collapse of vertebrae. ▪ Later: Thickened margins (due to irregular thickened new bone formation) leading to picture frame appearance Paget’s disease of Bone: M/E of Paget's disease: ▪ New woven bone with large blood filled spaces. ▪ Bones are not arranged around Haversian canals. ▪ Areas of new bone fit with old bone giving a mosaic appearance. Complications: 1. Fractures. 2. High output heart failure due to local increase of bone blood flow. 3. Malignancy: Mainly osteosarcoma (of old age). Other malignancies as fibrosarcoma, chondrosarcoma and giant cell tumor can occur. OSTEOPROSIS PATHOPHYSIOLOGY RISK FACTORS  Osteoporosis: Def: It is reduction of bone mass to a level below that required for normal bone support. However, mineralization is normal. Causes: A.Localized: Prolonged immobilization e.g. paralyzed limb. B. Generalized: 1. Senile osteoporosis: Occurs in postmenopausal women, after oophorectomy and elderly men Lack of estrogen plays an important role 2. Scurvy (vitamin C deficiency): Vitamin C is essential for the synthesis of collagen. 3. Osteogenesis imperfecta: Hereditary disease There is generalized disorder of collagen formation Bone cortex is formed mainly of woven bone and small areas of lamellar bone. This leads to deformities and fractures. 4. Endocrinal disturbances. 5-Radiation osteodystrophy: Inclusion of the growth cartilage plate in the radiation field leads to premature closure of epiphysis. 6-Renal osteodystrophy: Renal disorders leads to hypocalcemia: Damaged glomeruli leads to phosphate retention Ca /Ph ratio should be kept constant. This result in hypocalcaemia Tubular damage leads to decrease in the level of 1,25-dyhydroxy vitamin D. This results in hypocalcemia. With renal failure there is decreased intestinal absorption of Ca. This results in hypocalcemia. Hypocalcemia results in secondary hyperparathyroidism. This leads to Mobilization of calcium from bone and osteomalacia. 7-Endocrinal osteodystrophy: Increased steroids leads to increased rate of bone resorption. Hyperthyroidism leads to increase rate of bone resorption. Hyperparathyroidism leads to mobilization of calcium from bone. 8-Digital clubbing: Characters: o It affects mainly the fingers. o Nails are elongated, curved, raised and cyanotic. o Phalanges are thickened with subperiosteal new bone formation. Causes: Hypoxia, toxaemia, chronic lung diseases.  9-Vitamin D deficiency results in rickets in children and osteomalacia in adults A.Rickets Def: It is the childhood manifestation of a defect in bone mineralization. Age: It starts after 6 months (after exhaustion of calcium stores formed during intrauterine life). Etiology: Deficiency of vitamin D, Ca and phosphorous. This results from: 1.Insufficient exposure to sunlight. 2.Pre-maturity due to increased demands of Ca and due to defective hydroxylation of vitamin D in the liver. 3.Decreased intake or absorption of vitamin D. Rickets Etiology  1.Skeletal changes (N/E of skeleton): Skull: 1.Delayed closure of fontanelles and sutures. 2.Craniotabes (Flat occipital bone due to pressure during sleep on soft bones) 3.Square shaped head and frontal bossing. 4.Delayed dentition. Chest: 1.Rosary chest (prominence and beading of the costochondral junctions) 2.Pigeon chest (flattening of the sides and protrusion of the sternum). Vertebrae: Kyphosis, lordosis or scoliosis. Long bones: Bowing of legs and prominence of epiphyseal cartilage. Pelvis: Trefoil pelvis (triangular): This leads to obstructed labor in females. Osteomalacia Def: It is the adult manifestation of defective bone mineralization. Causes: Vitamin D deficiency due to: 1. Exposure to sun. 2. Increased demands (during lactation, repeated pregnancies). 3. Decreased absorption of vitamin D. Pathogenesis: Bone is a dynamic organ with balance between two processes; bone resorption and bone formation. In osteomalacia bone resorption proceeds as normal but bone formation proceeds with osteoid matrix deposition with failure of calcification resulting in bone softening. Clinical picture: Increased lumbar lordosis. Bending of femur and tibia. Contracted pelvis.