Download 2. Skeletal System

2. Skeletal System
Wednesday, 17 June 2015
11:32 am
Bones
• Very Strong
• Not inert i.e. grow/ decrease in size
• Compression strength ~170MPa
• (Steel ~300Mpa, aluminium ~80MPa)
• Lower tensile strength ~100-120 Mpa
• Very low shear stress strength ~50Mpa
Bone Stress Fractures (Overuse)
• Cumulative micro damage
• Excessive training/ inadequate recovery
• ('fatigue' fractures)
• Prevention role for HMS professionals
Stress Fractures across the lifespan
• Children
○ Greenstick fractures - young, 'softer' bone which bends and partially breaks
○ Bones become harder 'calcified' and more brittle with age
○ Young children 61% mineral content
○ Middle aged adults 66% mineral content
• Adolescents
○ Dissociation between timing of peak linear growth and peak bone mineral acquisition clinical significance during this short lag time is a temporary period of relative skeletal
weakness
○ Adolescent fracture incidence is at a peak during this period
• Aged
○ Osteoporosis (post menopausal fractures - decreased bone density/ length)
Loading Effects
• Bone is metabolically active - responds to mechanical stimuli by initiating or inhibiting bone
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• Bone is metabolically active - responds to mechanical stimuli by initiating or inhibiting bone
remodelling
• Animal and human studies - key features for osteogenic stimuli include load that is dynamic,
have high magnitude, high frequency and unusually distributed
Loading Effects
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Studies on Growing Animals
• Response of growing bone in young animals to moderate and intense physical activity
thoroughly reviewed
• Animal studies are incontrovertible in showing that growing bone has a greater capacity to add
new bone than the bone of adults
Maturity and Sex Dependant Loading Responses
• Prepubertal skeleton seems to have capacity to respond to loading by adding more bone in
periosteal (between skin and bone) surface
• Prepubertal boys show endosteal apposition in response to mechanical load whereas such as
response seems less likely in girls
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Bones - Segmental Growth
○ In terms of total leg length:
○ More growth occurs in the femur than in the tibia (55% vs 45%)
○ Also 2/3 more growth occurs at the knee end of the long bones than at the hip and ankle
ends (67% vs 33%)
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Bones - Maturational Differences
• Femoral Angle of Inclination
○ ~140-150 degrees in young
○ ~120 degrees in young
• Coxa valga often combined with genu varum (bow-leg)
• Coxa vara often combined with genu valgum (knock-knee)
• Kids have different skeleton when born and have walking problems etc.
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Human Skeleton
• Adult skeleton
○ 206 bones
○ ~270+ at birth
○ Hands and feet: ~half of the bones in skeleton
○ Femure: longest, heaviest, strongest bone. Length ~25% of an individuals height,
reasonable estimate of height of incomplete skeleton
• Appendicular Skeleton
○ 126 bones
○ Involved in movement through levers
• Axial Skelton
○ 80 bones
○ Involved in support and protection
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3. Muscular System
Thursday, 12 March 2015
10:02 am
Understanding Muscle Function
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• Biceps Curl
○ Agonist - Brachioradialis, biceps brachii and anterior deltoid
○ Synergist - Coracobrachialis
○ Stabilizers - rotator cuff
○ Antagonist - Triceps
Muscle Size and Loading
• Some people born with genetic predisposition to have stronger, larger faster muscles
• This muscle growth is regulated by myostatin
• Muscle size and strength is also affected by hormones e.g. peptide hormones (growth
hormones, insulin)
• Environmental factors such as nutrition also have significant impact. If muscles are unloaded
(e.g. space) it will have a negative affect on muscle and bone. Malnourishment also restricts
growth
Physical Inactivity
• When muscles are immobilized/ unweighted (e.g. limb casting, bed-ridden, micro-gravity)
there is a significant response from the muscles
• Decrease in muscle CSA (30% atrophy in 11 days) and a decrease in length
• Following major surgery (e.g. total knee arthroplasty) most significant clinical barrier is
persistent muscle atrophy and weakness
• Quadriceps as much as 40% weaker 2 months post surgery compared to healthy individuals
Physical Activity
• Muscle hypertrophy is not stimulated by long distance low intensity exercise
• Marathon running, endurance cycling --> minimal CSA change, increase in strength
• Weight training, sprint training --> increase in muscle CSA, increase in strength
• Combination training, kayaking --> increase in muscle CSA, hypertrophy
• Combination training --> increase hyperplasia in rats, could not get same change in humans,
no increase in number of muscle cells following birth
Myostatin
• Transforming growth factors (TGF-beta) member
• Negative regulator of muscle growth
• Inhibits myogensis: muscle growth and differentiation
• Double-muscling phenotype is a heritable condition
• Mutations lead to significantly more muscle mass hence stronger than normal
• Antibodies developed to neutralise myostatin, may be used therapeutically in treating muscle
washing or gene doping
Muscle Strain
• Muscle Tendon junction
• Excessive stretching while loading give predisposition to muscle strain
• Common in particular joints such as hamstrings
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4. Articular System
Thursday, 12 March 2015
11:31 am
Joint Component
• Joint is any place where two or more bones meet. Do not have to move with respect to one
another
• Joint components
○ Bones (2 or more)
○ Cartilage (tendons)
○ Ligaments (capsules)
○ Tendons (muscles)
Physical Activity Adaptations
• Immobilization
○ No impact loading
○ Size decreases
○ Mechanically weaker
○ Swimming
No impact loading
No change in size/ strength
• Moderate Activity
○ Endurance running
○ Size increase
○ Mechanically stronger
Extensors/ flexors differ
Time period of months
• High Intensity
○ Initial response
Size decrease/ no change
6 weeks
○ Adaptive response
Increased size/ strength
6/12 months
Physical Activity
• Cartilage
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Joint Function
• Immovable (synarthrisis)
• Slightly moveable (amphiarthrisis)
• Freely moveable (diarthrisis - synovial)
Joint range of motion
• Limiting factors restricting the range of motion in the joint
○ Capsule and ligaments
47%
○ Muscle Fasea
41%
○ Tendons
10%
○ Skin
2%
• Flexibility
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measurement technuiques
• It is now recognised as an applied branch of developmental biology called auxology
• Auxology cuts across many other fields of study including animal science, paediatrics, genetics,
obstetrics, orthodontics, nutrition studies, human movement studies etc.
We use Auxology within HMND Studies to:
• Monitor body changes to ensure the optimal growth and development of all children
• Evaluate growth for the purpose of encouraging the health and vigour of children and adults
over the life span
• It is an axiom of paediatrics that a healthy childhood lifestyle provides a strong basis for adult
health
• By modifying factors that predispose a child to marginal health, both the child and resultant
grown adult will benefit
Maternal Smoking and Birth Weight
• Babies born to smoking mothers weigh on average 170g less than babies born to non-smoking
mothers
• Neonatal mortality is 28% higher
Relative Age Effect (RAE)
• Successful athletes more likely to be born ealier in the selection year
• Relative age:
○ Difference in chronoligcal age between children in a single group
• RAE:
○ Consequences of relative age
○ Children born at the start of the year may be more advance in growth and development
than other children born at the end of the year
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Growth Spurt
• During the adolescent growth spurt, under the control of the endocrine system, whole
combinations of maturity events take place all of which are interrelated and occur in
sequence, although timing is highly variable
• For instance: Somatic development
○ The spurt in height, lean, strength etc. is very much tied in with sexual development, the
appearance of secondary sex characteristics, menarche etc.
Human Endocrine System
○ Hypothalamus = commander; regulates
○ Pituitary gland, releases:
Human growth hormone (HgH)
Trophic Growth hormones: regulate other endocrine glands that influence
adolescent growth changes
Changes in Age with Serum Testosterone
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Changes in age with serum Estradiol
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Blood levels of HGH in boys
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Timing of Events
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Timing of Events
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Measurement of Maturity Status
• Development of pre-pubertal childhood state to mature adult state is often evaluated in terms
of '4 aproaches'
1. Somatic characteristics
2. Sexual development
3. Skeletal development
4. Dental development
Skeletal (bone) Age
• Hand-Wrist X-rays: left hand and wrist (RUS)
• 27 bones in the and wrist
• Score/rate the ossification of the epiphyseal regions (growth plates/ end plates) to a healthy
'normative cohort'
There are 3 different techniques for determining skeletal age
1. Tanner Whitehouse method: (UK) takes the mean of individually rated bones
2. Greulich-Pyle (US): uses an atlas for comparison (lacks sensitivity)
3. Roche (Fels) (US)
• Classified as normal if within 2 years of chronological age
Dental Age: Demirjian System
• Basis: uses the eruption or non-eruption of teeth in the same way as the appearance and
ossification in bones
Developmental Variability is influenced by:
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9. Growth and Development 3
Wednesday, 17 June 2015
5:05 pm
Crude prediction of Adult height and weight
• Males/ Boys
○ 2 x height at age 2 years = adult height
○ 5 x weight at age 2 years = adult weight
• Females/ girls
○ 2 x height at age 18 months = adult height
○ 5 x weight at age 18 months = adult weight
• Growth in height and weight until onset of puberty
○ Height - 2-6cm/year
○ Weight 2.5kg/year
Adolescent Growth Spurt
• Boys
○ Add 20kg
○ Add 20cm
• Girls
○ Add 16cm
○ Add 16kg
Why, on average are males taller than females
• Magnitude of growth spurt is 2cm/year greater in boys
• On average, boys have 2 years more of pre-adolescent growth than girls (~5cm/yr for 2yrs)
• Girls stop growing ~age 16
• Boys continue until ~age 18
Affect of Gender on Growth and Health Patterns
• For a similar chronological age, girls are always closer to maturity than boys
• Girls are more resistant than boys to influences that might deflect them from their normal
growth pattern
• They are also easier to rehabilitate
• For almost all disease states, mortality is lower in women
• Life expectancy greater in women
• Overall, xx chromosome is healthier than xy combination
Gender Differences in Structural Growth Patterns
• Small structural differences between boys and girls untill the adolescent growth spurt
• Sexual dimorphism - phenotypic changes
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Estimated lean muscle mass in growing Girls and Boys
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