1 organic components (e.g. collagen) inorganic components (e.g., calcium and phosphate) 65-70% (dry...

1

Organic Components(e.g. collagen)

Inorganic Components(e.g., calcium and phosphate)

65-70%(dry wt) H2O

(25-30%)

one of the body’s hardest

structuresviscoelastic

ductile

brittle

Biomechanical Characteristics of Bone - Bone Tissue

25-30%(dry wt)

2

Strength and Stiffness of Bone Tissue

evaluated using relationship between applied load and amount of deformation

LOAD - DEFORMATION CURVE

Bone Tissue Characteristics

Anisotropic Viscoelastic Elastic Plastic

3

Stress = Force/Area Strain = Change in Length/Angle

Note: Stress-Strain curve is a normalized Load-Deformation Curve

4

elasticregion

plastic regionfracture/failure

Str

ess

(Lo

ad)

Strain (Deformation)

stressstrain

Elastic & Plastic responses

•elastic thru 3%deformation

•plastic response leads to fracturing

•Strength defined by failure point

•Stiffness defined as the slope of the elastic portion of the curve

5

Elastic Biomaterials (Bone)

•Elastic/Plastic characteristics

Brittle material fails before permanent deformation

Ductile material deforms greatly before failure

Bone exhibits both properties

Load/deformation curves

deformation (length)

load ductile material

elasticlimit

bone

brittle material

6

Anisotropic response behavior of bone is dependent on direction of applied load

Bone is strongest alonglong axis - Why?

7

fracture

fracture

fast

slow

Lo

ad

deformation

Viscoelastic Response behavior of bone is dependent on rate load is applied

Bone will fracture soonerwhen load applied slowly

8Compression Tension Shear Torsion Bending

Mechanical Loading of Bone

9

Vertebral fracturescervical fracturesspine loaded through heade.g., football, diving, gymnastics once “spearing” was outlawed in football the number of cervical injuries declined dramatically

lumbar fracturesweight lifters, linemen, or gymnastsspine is loaded in hyperlordotic(aka swayback) position

Compressive Loading

10

Tensile Loading

Main source of tensile load is muscle

tension can stimulate tissue growth

fracture due to tensile loading is usually an avulsionother injuries include sprains, strains, inflammation, bony deposits

when the tibial tuberosity experiences excessive loads from quadriceps muscle group develop condition known as Osgood-Schlatter’s disease

11

Shear Forces

created by the application of compressive, tensile or a combination of these loads

12

Relative Strength of Bone

13

Usually a 3- or 4-pointforce application

Bending Forces

14

Torsional Forces Caused by a twistingtwisting forceproduces shear, tensile, and compressive loads

tensile and compressive loads areat an angle

often see a spiral fracture developfrom this load

15

• axial skeleton– skull, thorax, pelvis, &

vertebral column

• appendicular skeleton– upper and lower

extremities

• should be familiar with all major bones

SKELETON

16

Purposes of Skeleton

• protect vital organs

• factory for production of red blood cells

• reservoir for minerals

• attachments for skeletal muscles

• system of machines to produce movement in response to torques

17

Bone Vernacular

• condyle– a rounded process of a bone that

articulates with another bone• e.g. femoral condyle

• epicondyle– a small condyle

• e.g. humeral epicondyle

18

Bone Vernacular

• facet– a small, fairly flat, smooth surface of a

bone, generally an articular surface• e.g. vertebral facets

• foramen– a hole in a bone through which nerves or

vessels pass• e.g. vertebral foramen

19

Bone Vernacular• fossa

– a shallow dish-shaped section of a bone that provides space for an articulation with another bone or serves as a muscle attachment

• glenoid fossa

• process– a bony prominence

• olecranon process

20

Bone Vernacular

• tuberosity– a raised section of bone to which a

ligament, tendon, or muscle attaches; usually created or enlarged by the stress of the muscle’s pull on that bone during growth

• radial tuberosity

21

Long Bones• e.g. femur, tibia

• 1 long dimension

• used for leverage

• larger and stronger in lower extremity than upper extremity– have more weight to

support

22

Short Bones

• e.g. carpals and tarsals

• designed for strength not mobility

• not important for us in this class

23

Flat Bones

• e.g. skull, ribs, scapula

• usually provide protection

24

Irregular Bones

• e.g. vertebrae

• provide protection, support and leverage

25

• e.g. patella (knee cap)

• a short bone embedded within a tendon or joint capsule

• alters the angle of insertion of the muscle

Sesamoid Bones

26

Long Bone Structure

cortical or compact bone (porosity ~ 15%) periosteum outer cortical membrane endosteum inner cortical membrane

trabecular, cancellous,or spongy, bone (porosity ~70%)

27

Long Bone Structureepiphyseal platecartilage separating metaphysis from epiphysis

epiphysisproximal and distal ends of a long bone

metaphysiseither end of diaphysisfilled with trabecular bone

diaphysis shaft of bone

28

Biomechanical Characteristics of Bone

Bone TissueRemodeling/Growth

Physical Activity Lack of Activity

Bone Deposits(myositis ossificans)

Age &Osteoporosis

Gravity Hormones

29

Longitudinal Bone Growth

– occurs at the

epiphyseal or

“growth “ plate– bone cells are produced on the

diaphyseal side of the plate– plate ossifies around age 18-25 and

longitudinal growth stops

30

Circumferential Bone Growth

– growth throughout the

lifespan– bone cells are produced on the

internal layer of the periosteum by osteoblasts

– concurrently bone is resorbed around the circumference of the medullary cavity by osteoclasts

31

Wolff’s Law

• bone is laid down where needed and resorbed where not needed

• shape of bone reflects its function– tennis arm of pro tennis players have

cortical thicknesses 35% greater than contralateral arm (Keller & Spengler, 1989)

• osteoclasts resorb or take-up bone

• osteoblasts lay down new bone

Biomechanical Characteristics of Bone

32

Bone Deposits• A response to regular activity

– regular exercise provides stimulation to maintain bone throughout the body

– tennis players and baseball pitchers develop larger and more dense bones in dominant arm

– male and female runners have higher than average bone density in both upper and lower extremities

– non-weightbearing exercise (swimming, cycling) can have positive effects on BMD

33

Bone Resorption

• lack of mechanical stress– Calcium (Ca) levels decrease– Ca removed through blood via kidneys

• increases the chance of kidney stones

• weightless effects (hypogravity)– astronauts use exercise routines to provide

stimulus from muscle tension• these are only tensile forces - gravity is compressive

35

Typical Vertical GRF during running

0

5

10

15

20

25

30

0 50 100 150 200 250 300

time (ms)

Fz

(N/k

g)

Heel-toe running pattern

Tip-Toe running pattern

36

TVISTreadmill Vibration Isolation andStabilization System

37

Changes in bone over timeEarly Years

• Osgood-Schlatter’s disease• development of inflammation, bony deposits, or an

avulsion fracture of the tibial tuberosity

• muscle-bone strength imbalance• “growth factor” between bone length and muscle

tendon unit (e.g., rapid growth of femur and tibia places large strain on patellar tendon and tibial tuberosity)

• during puberty muscle development (testosterone) may outpace bone development allowing muscle to pull away from bone

38

Changes in bone over timeEarly Years

• overuse injuries– repeated stresses mold skeletal structures

specifically for that activity– Little Leaguer’s Elbow

• premature closure of epiphyseal disc

– Gymnasts• 4X greater occurrence of low back pathology in

young female gymnasts than in general population (Jackson, 1976)

39

Changes in bone over timeAdult Years

• little change in length

• most change in density– lack of use decreases density

• DECREASE STRENGTH OF BONE

• activity– increased activity leads to increased

diameter, density, cortical width and Ca

40

Changes in bone over timeAdult Years

• hormonal influence– estrogen to maintain bone minerals– previously only consider after menopause– now see link between amenorrhea and

decreased estrogen - Female Athlete Triad

osteoporosisdisorderedeating

amenorrhea

low body fatexcessive training

low estrogenlevels

41

Changes in Bone Over TimeOlder Adults

• 30 yrs males and 40 yrs females– BMD peaks (Frost, 1985; Oyster et al., 1984)

– decrease BMD, diameter and mineralization after this

• activity slows aging process

42

Osteoporosis

HormonalFactors

NutritionalFactors

PhysicalActivity

OsteopeniaReduced BMD

slightly elevated risk of fracture

Severe BMD reductionvery high risk of

fracture(hip, wrist, spine, ribs)

28 million Americans affected – 80% of these are women10 million suffer from osteoporosis

18 million have low bone mass

43

Osteoporosis

• age– women lose 0.5-1% of their bone mass

each year until age 50 or menopause– after menopause rate of bone loss

increases (as high as 6.5%)

44

Do you get shorter with age?• Osteoporosis compromises structural

integrity of vertebrae– weakened trabecular bone– vertebrae are “crushed”

• actually lose height• more weight anterior to spine so the compressive

load on spine creates wedge-shaped vertebrae – create a kyphotic curve known as Dowager’s Hump

• for some reason men’s vertebrae increase in diameter so these effects are minimized

45

Preventing Osteoporosis

• $13.8 billion in 1995 (~$38 million/day)• Lifestyle Choices

– proper diet• sufficient calcium, vitamin D,• dietary protein and phosphorous (too much?)• tobacco, alcohol, and caffeine

– EXERCISE, EXERCISE, EXERCISE• 47% incidence of osteoporosis in sedentary population

compared to 23% in hard physical labor occupations (Brewer et al., 1983)

46

Osteoporosis, Activity and the Elderly

Rate of bone loss (50-72 yr olds, Lane et al., 1990)4% over 2 years for runners6-7% over 2 years for controls

However - rate of loss jumped to 10-13% after stopped running

suggest substitute activities should providehigh intensity loads, low repetitions (e.g. weight lifting)

47

Injury - Repetitive v. Acute Loading

frequency of loading

mag

nitu

de o

f lo

adin

g

injury tolerance(above this line injury will occur)

48

Articulations

• junction of 2 bones

• MOTION OCCURS AT A JOINT -- NOT AT A LIMB– i.e. elbow flexion NOT forearm flexion

49

Classification of joints

• Synarthroses - fibrous joint with little or no movement

• Amphiarthroses - cartilaginous joints with some motion

• Diarthroses - (aka synovial) - freely movable joint

51

Joint Classification

• based on – number of axes of rotation– number of planes of motion– e.g. uniaxial -- 1 axis of rotation so 1 plane

of motion

52

Condyloid = Biaxiale.g., flexion & extension

internal & external rotation

Ball and Socket = Triaxiale.g., flexion & extension

internal & external rotationabduction & adduction

53

Hinge = uniaxiale.g., flexion and extension

Pivot = uniaxiale.g., supination& pronation

54

Gliding = no axes‘gliding between

2 flat bones’

Saddle = biaxialsame as condyloidbut greater ROM

Ellipsoidal = biaxiale.g., flexion & extensionabduction & adduction

55

Structure of Synovial Joint

A - articular (hyaline) cartilage (1-7 mm)– smooth elastic tissue on

ends of bone– 60-80% water– no blood supply– absorbs shock,

distributes force and provides a low friction surface

56

Structure of Synovial JointB - fibrous capsule

– very fibrous collagen tissue used to hold bones together

C - synovial membrane– lines the joint cavity– secretes synovial fluid to

lubricate and provide nutrition

NOTE: B & C combine to form the articular capsule

or joint capsule

57

Structure of Synovial Joint

D - ligaments– connect bone-to-bone– usually restrict ROM

at a joint

• tendons (not shown)– connect muscle-to-

bone

A* - Joint cavity

58

Other Structures of Synovial Joints

• bursa– small capsules lined with

synovial membranes– reduces friction between other

structures in the joint

• tendon sheaths– fascia surrounding tendon to

reduce friction between tendon and surrounding structures

Olecranon bursa

Digital synovial sheath

59

Other Structures of Synovial Joints

articular fibrocartilage – different from articular cartilage– takes the form of a

fibrocartilaginous disc or partial disc• distributes load over joint surface• improve fit of articulating surfaces• limit slipping of one bone relative to

other• protect periphery of articulation• lubricate articulation• absorb shock

60

Arthritis• Refers to more than 100 different diseases that affect areas in or around joints.

• The disease also can affect other parts of the body.

• Arthritis causes pain, loss of movement and sometimes swelling.

•Affects women more than men

Source: Arthritis Foundation – www.arthritis.org

61

Arthritis

Osteoarthritis20.7 million

Mostly after age 45Rheumatoid2.1 million

Mostly women

Fibromyalgia3.7 million

Mostly women

Gout2.1 million

Mostly men

Spondylarthropathies412,000

JuvenileArthritis285,000

Under age 17

Juvenile RheumatoidArthritis (JRA)

50,000 Lupus239,000


62

Osteoarthritis (OA), or degenerative joint disease, is one of the oldest and most common types of arthritis, characterized by the breakdown of the joint's cartilage. Cartilage is the part of the joint that cushions the ends of bones. Cartilage breakdown causes pain and joint swelling. With time, there will be limited joint movement.

• Most commonly affects middle-aged and older people

• Range from very mild to very severe

• Affects hands and weight-bearing joints (e.g., knees, hips, feet and back).

• OA is not an inevitable part of aging, although age is a risk factor

• Obesity may lead to osteoarthritis of the knees

• Joint injuries due to sports, work-related activity or accidents may be at increased risk of developing OA.


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• Characterized by the inflammation of the membrane lining the joint, which causes pain, warmth, redness and swelling.

• The inflamed joint lining, the synovium, can invade and damage bone and cartilage.

• Inflammatory cells release enzymes that may digest bone and cartilage.

• The involved joint can lose its shape and alignment, resulting in pain and loss of movement.

• The disease usually begins in middle age, but can start at any age, and affects two to three times more women than men.

Rheumatoid Arthritis (RA) – a systemic disease that affects the entire body.


64

Fibromyalgia syndrome is a condition with generalized muscular pain and fatigue that is believed to affect approximately 3.7 million people.

Location of “Tender Points”

• The name fibromyalgia means pain in the muscles and the fibrous connective tissues (the ligaments and tendons). The condition is known as a syndrome because it is a set of signs and symptoms that occur together.

• Fibromyalgia mainly affects muscles and their attachments to bones. Although it may feel like a joint disease, it is not a true form of arthritis and does not cause deformities of the joints. Fibromyalgia is, instead, a form of soft tissue or muscular rheumatism.


65

Arthritis Treatments

Medicines(e.g., analgesics, NSAIDS,

DMARDS, Disease ModifyingAnti-Rheumatic Drugs)

Physical/Occupational Therapy• recommend and teach prescribed muscle strengthening and range-of-motion exercises• teach non-medication ways to control pain• suggest ways to make everyday and work activities easier

RestMore rest and less activity are needed during flares and the

opposite is true during periods of improvement.

Surgeryjoint replacement

Use of Heat or ColdHelpful before and after exercise

Many respond better to cold packs than to heat

Use of Heat or ColdHelpful before and after exercise

Many respond better to cold packs than to heat

Diet• Lack of vitamins associated with progression of OA of the knee • Connection between obesity and OA of the knee• Diet high in Omega 3 fatty acids may help reduce inflammation in RA• In general, people with arthritis are urged to maintain a balanced diet and stay close to their ideal weight.

Joint ProtectionCareful use of joints to limit the pressure on the

involved jointSimple and inexpensive devices available

Exercise(see next slide)


66

Exercise• Proper exercises performed on a daily basis are an important part of arthritis treatment.

• Exercise to help reduce weight can help prevent osteoarthritis in the knee.

• Proper exercise helps build and preserve muscle strength, keep joints flexible and help protect joints from further damage.

Two categories of exercise:

• Therapeutic -- Prescribed by a doctor, physical therapist or an occupational therapist. These exercises are based on individual needs and are designed to reach a certain goal.

• Recreational -- Includes any forms of movement, amusement or relaxation that refreshes the body and mind. These exercises add to a therapeutic program, but do not replace it.

Three types of exercises:

•Range-of-motion -- Moving a joint as far as it comfortably will go and then stretching it a little further. Range-of-motion exercises are designed to increase and maintain joint mobility that will decrease pain and improve function.

•Strengthening -- Increases muscle strength to stabilize weak joints. These exercises use the muscle without moving the joint.

•Endurance -- This type of exercise includes walking, swimming, bicycling, jogging, dancing and skiing. These dynamic forms of exercise increase endurance, whereas range-of-motion and strengthening do not. The most common risk in exercising is injury to joints and muscles. This usually happens from exercising too long or too hard, especially if a person has not been active for some time.


67

close packed position– maximum contact

area

– minimum mobility

– maximum stability

close-packed vs. loose packed

68

Bony Stability (cont.)

• amount of contact area

69

Joint Stability - Connective Tissue

• ligamentous support

70

Properties of Connective Tissue

• elasticity– ability to return to normal state after stretch– elastic limit

• stretch beyond this limit will cause permanent damage

• plasticity– stretched too far such that does not return to

its normal state• ligament sprain (worse than bone fracture)

71

deformation (length)

load

elas

tic

plastic

elasticlimit

Sprains occur in this region

Sprains resultin decrease ofjoint stability

Exercisewill helpincreasethe loadsa ligamentor tendoncan sustain

72

Joint Stability - Muscles

• muscular arrangement– ability of muscle to

provide support– muscle fatigue

• cruciate rupture more likely when muscle is fatigued

73

Mobility

• degree to which an articulation is allowed to move before being restricted by surrounding tissues

• ROM a.k.a. flexibility

74

Stability v. Mobility

• trade-off between stability and mobility

–increase stability decrease mobility

–vice-versa

1 organic components (e.g. collagen) inorganic components (e.g., calcium and phosphate) 65-70% (dry...

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