metabolic disorders of bone
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Metabolic Disorders of Bone
Metabolic Disorders of Bone ByDr Akkad Rafiq Bone Structure Three main functions of bonesupport,protection leverageCompositionType I collagen fibers,mineral componentOther non-collagenous proteins Osteopontin osteonectinOsteocalcin alkaline phosphatasesBone morphogenetic protein
Bone Minerals Almost half the bone volume is mineral mattermainly calcium and phosphate in the form of crystalline hydroxyapatite
demineralization of bone occurs only by resorption of the entire matrix
Bone Cells Osteoblasts - concerned with bone formation and osteoclast activationOsteocytes -These cells can be regarded as spent osteoblastsOsteoclasts- These cells are the principal mediators of bone resorptionBone structure The mature tissue is lamellar bone, in which the collagen fibres are arranged parallel to each other to form multiple layers with the osteocytes lying between the lamellae.
Minerals of bone CalciumMagnesiumVit DPhosphorusCalcitonin
Osteoporosisclinical disorder characterized by an abnormally low bone mass and effects in bone structure, which renders the bone fragile and at greater risk of fracture in a person of that age, sex and race.Pathology:results from an unhealthy imbalance between two normal activities of bone: bone resorption and bone formation.
The combined processes of bone resorption and bone formation allow the healthy skeleton to be maintained continually by the removal of old bone and its replacement with new bone. Pathology the destruction of bone begins to exceed the formation of bone; this imbalance leads to a net loss of bone, and the beginnings of osteoporosis.PRIMERY RISK FACTORSCaucasoid (white) or Asiatic ethnicityFamily history of osteoporosisHistory of anorexia nervosa and/or amenorrhoeaLow peak bone mass in the third decadeEarly onset of menopauseUnusually slim or emaciated buildEarly hysterectomyNutritional insufficiencyChronic lack of exerciseCauses of secondary osteoporosisNutritionalMalabsorptionMalnutritionScurvyInflammatory disordersRheumatoid diseaseAnkylosing spondylitisTuberculosisDrug inducedCorticosteroidsExcessive alcohol consumptionAnticonvulsantsHeparinImmunosuppressivesEndocrine disordersGonadal insufficiencyHyperparathyroidismThyrotoxicosisCushings diseaseMalignant diseaseCarcinomatosisMultiple myelomaLeukaemiaOtherSmokingChronic obstructivepulmonary diseaseOsteogenesis imperfectaChronic renal diseaseInvestigations X-ray findings are generally insufficient
cannot reliably measure bone density useful to identify spinal factures, explains back pain, height loss or kyphosis.
X-rays may detect osteopenia only when bone loss is > 30%.
Patient who had a severe fracture and a moderate fracture in her spine. Three years later a second xray revealed a new fracture. These fractures were in the lower spine.
Radiographic Fracture Assessment
DEXADual energy x-ray absorptiometry (DEXA) This is the most popular and accurate test to datenon-invasiveinvolves no special preparation. Radiation exposure is minimal,Can be used to measure bone mineral density in the spine, hip, wrist, or total body.
expensive not portable.
Screening- Ultrasound Densitometryinexpensive, portable\ no radiation can be used only in peripheral sites (eg, the heel),
Fracture ReductionGoal: prevent fracture, not just treat BMDOsteoporosis treatment optionsCalcium and vitamin DCalcitoninBisphosphonatesSelective Estrogen Receptor ModulatorsParathyroid HormoneOsteoporosis Treatment: Calcium and Vit DCalcium and Vit D supplementation shown to decrease risk of hip fracture in older adults1000 mg/day standard;1500 mg/day in postmenopausal women/osteoporosis
Vitamin D (25 and 1,25): 400 IU/DayOsteoporosis Treatment: Bisphosphonates Decrease bone resorptiondecrease hip and vertebral fracturesAlendronate, risodronate POIV: pamidronate, zolendronateIbandronate : once/month
Calcetoninnot as effective as Bisphosphonates200 IU nasally/day
Osteoporosis Treatment: Selective Estrogen Receptor ModulatorsRaloxifene Decrease bone resorption like estrogenNo increased risk cancer (decrease risk breast cancer) Osteoporosis Treatment: PTHTeriparatideINTERMITTENT PTH: overall improvement in bone densityCurrent GuidelinesUS Preventive Task Force Test Bone Mineral Density in all women over age 65, younger postmenopausal women with at least one risk factor, and postmenopausal women with a history of fractureTreat patients with T score