Osteoporosis: key concepts


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Osteoporosis: key concepts
Azeez Farooki, MD Endocrinologist

Outline
I) Composition of bone II) Definition & pathophysiology of osteoporosis III) Peak bone mass IV) “Secondary” osteoporosis V) Vitamin D insufficiency / deficiency VI) Fracture risk VII) Pharmacotherapies

Characteristics of Bone
• Bone functions as1:
– Mechanical scaffolding – Metabolic reservoir (calcium, phosphorous,
magnesium, sodium)
• Bone contains metabolically active tissue capable of2:
– Adaptation to load – Damage repair (old bone replaced with new) – Entire skeleton remodeled ~ every 10 yrs
Shoback D et al. Greenspan’s Basic and Clinical Endocrinology. The McGraw-Hill Companies, Inc.; 2007. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=13. Gupta R et al. Current Diagnosis & Treatment in Orthopedics. The McGraw-Hill Companies, Inc.; 2007. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=20.

Definition of osteoporosis
• A disease characterized by: – low bone mass and, – structural deterioration of bone tissue
• leads to bone fragility & susceptibility to fractures (commonly: spine, hip & wrist)
• Silent until a fracture occurs

T-score: standard deviations away from average sex matched 30 year old
rel risk fracture by 1.5-2.5x per SD

T-Score (SD)

Normal

-1 and above

Low bone mass (osteopenia)

-1 to -2.5

Osteoporosis

< -2.5

SWehvy e-2r.e5? Yielded 17% prevalence of osteoporosis [email protected] among wo similar to the estimated 15% lifetime risk of hip

fracture for 50 yo white women in US WHO task force 1994

Bone density is a major determinant of fracture risk

Relative Risk of Fracture

35

30
Osteoporosis
25
20
15

Low Bone Mass

Normal

10

5

0 -5 -4 -3 -2 -1 0 1 2

BMD T-Score

Meunier P. et al. Clin Ther 1999: 21:1025

Bone Strength: NIH consensus Statement 2000

Bone Strength

Bone
= Quality

Bone
+ Density

•Structure & Architecture •Turnover •Mineralization •Damage accumulation

DXA (dual energy X-ray absorptiometry) • grams / cm2

Impairments in Bone Mass and Quality in Osteoporosis
Strength of osteoporotic bone is impaired by: • Loss of bone mass • Reduction in bone quality:
• Loss of horizontal struts • Loss of connectivity • Conversion of trabecular plates to rods • Resorption pits are “stress concentrators” • Unfavorable geometry
Young normal
Images courtesy of Ralph Müller

Physiologic Bone Remodeling: In osteoporosis: imbalance causes net
bone loss

Unbalanced Remodeling in Menopause Leads to Osteoporosis
Effects of Aging Estrogen Deficiency

Bone Resorption

>

Bone Formation

Net Bone Loss
Shoback D et al. Greenspan’s Basic and Clinical Endocrinology. The McGraw-Hill Companies, Inc.; 2007. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=13. Tortora GJ et al. Principles of Anatomy and Physiology. John Wiley & Sons, Inc.; 2003:162-184.

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Osteoporosis: key concepts