Osteoporosis Educational Series, Lecture 2of 3: Understanding Bone to Understand Osteoporosis: Pathogenesis and Risk Factors

Nahid Rianon, M.D., Dr.P.H.The University of Texas Health Science Center at Houston

Goal and ObjectivesGOAL: The goal of this presentation is to describe detail

mechanism of bone loss and risk of fractures

LEARNING OBJECTIVES:At the end of this presentation, attendees will be able to

Explain normal and abnormal state of bone metabolism Define bone remodeling Identify risk factors for bone loss Calculate risk of facture

What percent of adult human bone is made of minerals? a) 20% b) 65%c) 75%d) 90%

Pre QuizQuestion 1 of 5

Which of the following factors stimulate osteoblasts? (Choose one)

a) Glucocorticoids and Estrogenb) Thyroxine and Androgenc) Estrogen and Growth Hormone d) Vitamin D and Thyroxine

Pre QuizQuestion 2 of 5

Which one of the following statements best fits the pathological state of osteoporosis due to age related bone loss?

a) Bone formation and resorption are in balanceb) Both formation and resorption slows down at the same ratec) Both formation and resorption increases at the same rated) Bone resorption is greater than bone formation

Pre QuizQuestion 3 of 5

Which of the following diseases is not considered a risk for developing secondary osteoporosis (when remains untreated) for FRAX calculation tool?

a) Diabetes Mellitus type IIb) Hypothyroidismc) Diabetes Mellitus type Id) Osteogenesis Imperfecta in adults

Pre QuizQuestion 4 of 5

Pre QuizQuestion 5 of 5

In humans, trabecular bone volume is larger than cortical bone volume?

a) Trueb) False

Function

Mechanical Weight bearing Protection for soft organs Attachment for muscles

Mineral reservoir Calcium Phosphorus

Why Do We Need Strong Bones:

Overall

Organic Matrix 10% of adult bone Primarily protein collagen -provides flexibility

Mineral Component 65% of adult bone Hydroxyapatite - insoluble salts of calcium (99%) & phosphorus (85%) Very little Mg, Na & HCO3

Water 25% of adult bone

Bone Structure

Cellular

Osteoblasts Critical to bone formation

Osteoclasts Reabsorb bone

Osteocytes Exact role is still under investigation

Bone Structure

Osteoblasts

Osteoclasts

Osteocytes

Types of bone Forces on bone

Trabecular 20% of skeletal mass Greater surface area than cortical Provides supporting strength to

the ends of weight-bearing bones

Cortical 80% of skeletal mass Solid outside shaft of long bones

Compressive stress From body weight pushing the

bone down

Tensile stresses From muscles, pulling the bone

apart

Bone Structure

Trabecular and Cortical Bones

Trabecular bone Cortical bone

Femur with loss of mineral and microstructure

Healthy femur

Tensile

Comprehensive

Mineral loss

Physiology- Normal State

Bone Marrow Progenitors

Osteoblast Precursor Osteoclast Precursor

Glucocorticoids Estrogen Calcitonin

Estrogen AndrogensGH/IGF-1

Thyroxine Vitamin A

Osteoblast

New Bone Formation

Bone Resorption

Osteoclast

Osteocyte

1,25 OHDPTH

+

_ _

*Find out if this is 1,25 (OH)2D

+

Pathogenesis Of Osteoporosis - Bone Remodeling

Normal Bone Remodeling Sequence

Resorption = Formation No change in bone mass

LEGEND: LC = Lining Cells CL = Cement Line OS = Osteoid BRU = Bone Remodeling Unit

OsteoclastPrecursor

OsteoclastOsteoblastPrecursors Osteoblast

MononuclearCells

High bone turnover state

Unbalanced remodeling

Osteoporosis

Basic Pathology

Normal Bone Structure

OsteoporoticBone Structure

Resorption > Formation Net bone loss

Unbalanced Remodeling & Osteoporosis

Influencers:

• Inadequate calcium or vitamin D

• Menopause

• Aging

• Medications or diseases

Increasing age Female gender Early menopause Low body weight Previous fracture Family history Low calcium intake

Low vitamin D Alcohol Smoking Physical inactivity High caffeine intake Drug use- steroid White or Asian race

Osteoporosis Risk Factors

FRAX Calculator

Age (40-90), gender, height & weight

Previous fracture Hip fracture in parents Current smoking Alcohol Glucocorticoids (oral) ≥ 3

months @ dose 5mg daily or more

or equivalent doses of other glucocorticoids

Rheumatoid arthritis Secondary osteoporosis

DM-I, OI in adults, Untreated hyper or

hypothyroidism, Premature menopause (< 45

yrs), Chronic malnutrition or

malabsorption & Chronic liver disease

Bone mineral density (BMD)

FRAX Risk Factors

Post QuizQuestion 1 of 5

What percent of adult human bone is made of minerals? a) 20% b) 65%c) 75%d) 90%

Post QuizQuestion 2 of 5

Which of the following factors stimulate osteoblasts? (Choose one)

a) Glucocorticoids and Estrogenb) Thyroxine and Androgenc) Estrogen and Growth Hormone d) Vitamin D and Thyroxine

Post QuizQuestion 3 of 5

Which one of the following statements best fits the pathological state of osteoporosis due to age related bone loss?

a) Bone formation and resorption are in balanceb) Both formation and resorption slows down at the same ratec) Both formation and resorption increases at the same rated) Bone resorption is greater than bone formation

Post QuizQuestion 4 of 5

Which of the following diseases is not considered a risk for developing secondary osteoporosis (when remains untreated) for FRAX calculation tool?

a) Diabetes Mellitus type IIb) Hypothyroidismc) Diabetes Mellitus type Id) Osteogenesis Imperfecta in adults

In humans, trabecular bone volume is larger than cortical bone volume?

a) Trueb) False

Post QuizQuestion 5 of 5

Questions?

Thank You

Reference

• American Society for Bone and Mineral Research http:www.asbmr.org• WHO Fracture Risk Assessment Tool (FRAX)

http://www.sheffield.ac.uk/FRAX/tool.jsp

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