Bones Online

8/2/2019 Bones Online

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Sherif Elsobky


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Cannot teach you all about bones

The aim of the lecture is to highlight topicsyou need to know

Emphasise the basic principles that will helpyou pass your exam

Test what you know


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Bone:

Composition

Structure

Function

Ca2+

Osteoporosis

Other clinic topics


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Mechanical

Mineral storage

Haemopoietic


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What are the three main components theform the bones microstructure??


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Matrix, organic and inorganic

Organic Type 1 collagen Non organic carbonated hydroxyapatite Matrixcells

Osteoclasts, osteocytes and osteoblasts


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Cells OsteoBlasts: Broduce bones

Osteocytes: Maintains bones -most numerous

stuck in lacunae, stellate processes OsteoKlasts: Kills bone


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Compact tissue - the harder, outer tissue ofbones

Cancellous tissue - the sponge-like tissueinside bones.

Subchondral tissue - the smooth tissue at theends of bones covered with cartilage.


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Layer of spongy bone sandwiched between parallellayers of compact boneb. Periosteum covers compact bonec. Endosteum covers spongy bone

Hematopoietic tissue: Red marrowRed marrow cavities

i. Spongy bone of long bones

In adults, fat containing medullary cavity extends

into epiphysisi. Little red marrow


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Outline the difference between woven andlamellar bone???


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LAMELLAR WOVEN

Arrangement of Type I collagen parallel IrregularOsteocytes in matrix few Numerous

Osteocyte morphology uniform PleomorphicDeposition/production slow Rapid

Tensile strength strong LowPresent in adult skeleton Normal AbnormalFound in bone forming tumor rare Usual

Pathologic formation Reaction to persistentstress and slowlygrowing tumors

Reaction to rapidlygrowing tumor or virulentinfection


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Outline the 5 distinct zonesof endochondral

ossification?


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From cartillage to bone"Real People Have Calcified Osses":Resting zone (reserves)ProliferationHypertrophyCalcificationOssification


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Bone needs to be replaced. Resorbs andreforms

Osteoblasts and Osteoclasts work together

1. PTH +Osteoblasts + Collagenase &Osteoclasts Bone reabsorbed

2. Remodelling Osteoblasts Osteoid -->Bone formed

Osteoid= collagen


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PTH stimulates Osteoblasts Osteoblasts stimulates Osteoclasts and

Collagenase which reabsorb bone

Coupling signals stimulate Osteoblasts toform Osteoid (mineralization).

Osteoblasts flatten and deactivate


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Physiology


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What is the normal Ca2+ range?

5 functions of calcium ?


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Normal range of calcium is 2.1-2.6 mmol/

Function of Calcium

Contractility of cardiac muscles depends on extracellular Ca2+ (ligand for cellmembrane depolarisation)

Contractility of skeletal muscles depends on intracellular Ca2+ (actual

mechanism for contraction) Plasma membrane ion channel activities

Transmission of nervous impulses

Enzyme activities

Maintenance of bones and teeth

Blood clotting

Calcium Regulation 99% found in bones and 1% soluble in cells and bloodplasma (in dynamic equilibrium)


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Parathyroid hormone (parathyroid gland) Calcitonin (thyroid gland)

PTH released in response to low ioniccalcium in blood

Osteoclasts are activated to digest bonematrix and release calcium into blood

Calcitonin is released in response to highcalcium in blood

Calcium salts are deposited into bone


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40% of eaten Ca++ is absorbed through the

small intestine

Through epithelial receptor called Calbindin Sats depend on 1,25-dihydroxvitamin D

Excretion mainly though kidneys


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Secreted by thyroid gland

lower plasma calcium

Effects: Kidneys Decrease calcium reabsorption

Bones Inhibits bone resorption by osteoclasts

Less potent than PTH


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What are the six characteristics of synovialjoints??


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1There is ajoint cavity2.The parts of the bones in contact with eachother are covered by smooth articular cartilage.

3. The joints are surrounded by a connectivetissue capsule

4. The inner surface of the capsule and thenon-articular surfaces of the bones are covered

with synovial membrane5. The capsule is reinforced by ligaments

6. The joint is capable of movement


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Synovial joint Three joint in one (Medical tibiofemoral joint,

later TFJ and patellofemoral joint)

Unstable (due to weight) hence susceptible toinjury

Ligaments and meniscus


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Flexion

Extension Rolling

Rotation


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Which muscles provide knee stability?


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Four ligaments: Collaterals (M+L), Cruciate (A+P) Functions:

Stability

Limiting movements

Protect the articular capsule

Meniscus: Fibrocartilage discs

Medial and lateral

Shock absorbers

Reduce friction


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Menisci attachments in knee Each meniscus has something attached to it.

The medial meniscus has the medialcollateral ligamentThe lateral meniscus is attached to thepopliteal muscle.


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Cruciate ligaments: insertionsPAMS APPLES:Posterior [passes] Anterior [inserts] Medially.Anterior [passes] Posteriorly [inserts]Laterally.


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Small fluid filled sac that reduces friction Prepatellar bursa: Between the patella and

skin

Infrapatellar bursa: Between tibia and patellarligament

Suprapatellar bursa: Inf femur and quadsmuscle


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Knee injuries


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Which menisci is more likely to get damageand why?


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Medial meniscus is torn more often than the lateral lateral meniscus is smaller in diameter, thicker in periphery,wider in body and more mobile

Damage usu due to mechanical stresses produced from:

Acceleration and deceleration

Coupled with sudden change in direction and landing aftera jump (eg basketball and football)

Injuries commonly occur usually when the knee is flexedand there is significant rotation between the femur andtibia


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Ligaments can be damaged together or in isolation Occurs when a joint is loaded in the direction in which theligament resists movement: MCL snaps when forcing knee into valgus LCL snaps when forcing knee into varus

Valgus outward angulation of the distal segment of a bone or joint(causing knee to point medially)Varus inward angulation of the distal segment of a bone or joint (causingknee to point laterally)


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In young people with strong bones, theligaments are usually relatively weaker andwill be the first to be injured

The converse is true in elderly people withweak bones


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ACL damage

Medial meniscus damage

MCL damage


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Fractures around the knee can be associated

with injuries to other structures

Transverse fractures in the patella may occur due to quadriceps contracting suddenlyagainst a resistance

May predispose to osteoarthritis (especiallywhen articular surfaces are involved)


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How would you test for an Anterior cruciateligament tear clinically?

Anterior draw test, Lachmans test

How would you test for menisci tear McMurrays test

If you cant remember the name in exam describe howyou do it


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Occurs when a force exceeds the compressive ortensile strength of the bone highest incidence is seen in young males between ages 15-

24 (tibia, clavicle and distal humerus) and usually the resultof trauma.

In the elderly, fracture of proximal femur, proximal humerus,vertebrae, distal radius, or pelvis are often associated with

osteoporosis.


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Stage ofHaematoma Blood vessels break and leaking blood produces a haematoma

Stage of Subperiosteal and Endosteal Cellular Proliferation osteoblasts and chondroblasts are activated and proliferate at

periosteum and endosteum

Stage ofCallus Chondroblasts lay down hyaline cartilage & Osteoblasts lay down

collagen fibres which then calcifies to form woven bone

Stage ofConsolidation Osteoblasts lays down lamellar bone at the expense ofwoven bone

Stage ofRemodelling Bone is gradually remodelled to original state


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Osteoporosis


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Define osteoporosis

A bone mineral density that is 2.5 SDS or more below the mean peakbone mass (average of young, healthy adults) as measured by DEXA scan


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Osteoporosis is a bony disorder characterizedby progressive decrease in bone density andmass

Osteon is bone and porosis is hole in Greek


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Female male ratio 4:1 and higher incidence ofmale osteoporosis

Up to 50% postmenopausal women affected

One in ten older women with a previousfragility fracture has a referral for bone

density assessment in her electronic medicalrecord


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Describe the risk factors of osteoporosis?


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History of fracture as an adult and in animmediate (first-degree) relative Low body weight Lifelong low calcium intake

Current cigarette smoking Alcoholism Advanced age

Early menopause

Asian


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Clinical picture Serological Se Calcium, Phosphorus and

Alkaline Phosphatase.

Other markers from blood and urine

Gold standard- DXA


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Two X-ray beams with differing energy levelsare aimed at the patient's bones

a method of estimating the strength of bonesand the likelihood of bone fractures with

minimal or no trauma On X-ray you will see changes only after 30-

40% bone loss


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Define T score and Z scores??

T score number of standard deviations above or belowthe mean for a similar healthy30 year old

Z score number of standard deviations above or belowthe mean for the patients age, sex and ethnicity


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Clinical Loss of bone mass sufficient to significantly increase the

risk of fracture

Diagnostic

T score

number of standard deviations above or belowthe mean for a similar healthy30 year old

Normal BMD = T: 0 to -1

Osteopenia BMD = T: -1 to -2.5

Osteoporosis BMD = T: less than -2.5 Z score number of standard deviations above or below

the mean for the patients age, sex and ethnicity


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Are as important as any medication Nutritional

Calcium

Vitamin D

Vitamin A

Lifestyle Smoking

Exercise

Falls risk reduction


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Bisphosphates- Most effective

Parathyroid hormone

Selective Oestrogen Receptor Modulators

Denosumab


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Excessive uncontrolled destruction of bone byabnormally large and active osteoclasts

Concurrent inadequate attempts at

haphazard new bone formation byosteoblasts

Produces physically weak woven bone

Very high alk phos, normal Ca2+ and Po4


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Vitamin D deficiency Normal collagen production but

mineralization is inadequate

Leads to trabecular bone that is only partiallymineralised and is therefore soft and weak

Low Ca++, high PO4, Normal Alk Phos, HighPTH


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