Understanding the Mechanics of Injury

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Chapter 15

• Understanding the Mechanics of Injury

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Stress

• Controlling the level of imposed stress is
  important in training various tissues and
  avoiding injury.

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Stress Continuum (Fig 15.3, 343)

• Distress (Causes malfunction)
• Pathologic underload zone
• Pathologic overload zone
• Eustress (Causes positive adaptation)
• Physiologic loading zone
• Physiologic overload (training) zone

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Relationship of magnitude and frequency to type
of injury (Fig 15.5)

• Acute loading
• a single stress of sufficient magnitude to cause
  injury to a biological tissue. (Macrotrauma)
• Repetitive loading
• repeated application of a subacute stress that is
  usually of low magnitude (Microtrauma)

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Injury Acute Definition (CDC)
Injury is defined as physical damage to an
individual that occurs over a short period of
time as a result of acute exposure to one of the
forms of physical energy in the environment, or
to chemical agents, or the acute lack of oxygen.
Excluded from this definition of injury are
cumulative trauma disorders, musculoskeletal
disorders of the back not caused by acute trauma,
and effects of repeated exposure to chemical or
physical agents. The three phases of injury
control are defined as prevention, acute care,
and rehabilitation.
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Three Major Categories of Injury
Intentional injuries result from interpersonal or
self-inflicted violence, and include homicide,
assaults, suicide and suicide attempts, child
abuse and neglect (includes child sexual abuse),
intimate partner violence, elder abuse, and
sexual assault. Unintentional injuries include
those that result from motor vehicle collisions,
falls, fires, poisonings, drownings,
recreational, and sports-related activities.
Occupational injuries occur at the worksite and
include unintentional trauma (for example,
work-related motor-vehicle injuries, drownings,
and electrocutions), and intentional injuries in
the workplace.
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Williams model of overuse injury (1993)
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Williams model of overuse injury (1993)
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Williams model of overuse injury (1993)
Decrease Training Effort
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Preventing overuse injury in young pitchers
controversy
Split finger fastball vs Change up? Pain vs
soreness? 75 pitch limit vs Complete
Game? Science vs Tradition
Click on picture to read more
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Fractures pain, deformation, disability
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Types of Fractures

• Simple - no break in skin.
• Compound - protrusion through the skin.
• Comminuted - fragmentation of the bone.
• Avulsions - bone chip pulled away
• Spiral - twisting break.
• Impacted - opposite ends compressed together.
• Stress - repeated low magnitude loading

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Site of Ankle Avulsion Fracture
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Avulsion fracture of the patella following
B-PT-B repair of the ispsilateral ACL
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Comminuted Fracture
Low Energy
High Energy
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Ankle Trouble
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Surgical BonePlates
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Types of Fractures
What is the error?
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Three Biological Phases to fracture healing

• Inflammatory Phase
• 3 to 7 days
• immobilize the bone
• activates cells for repair
• step by step process that is critical to
  successful union

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Three Biological Phases to fracture healing

• Inflammatory Phase
• Reparative Phase (bony union)
• about one month
• callus formation
• provisional gt bony

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Three Biological Phases to fracture healing

• Inflammatory Phase
• Reparative Phase (bony union)
• Remodelling Phase
• restoration of original contour

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Changes in ACL surgery

• Anterior Cruciate Ligament
• Prevents anterior translation of tibia relative
  to the femur
• 3rd degree sprain of ACL
• Ruptured ACL
• Torn ACL
• Early 1980s
• B-PT-B surgery
• Patella
• Patellar tendon (ligament)
• Tibia Tuberosity

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Changes in ACL surgery

• Now performed arthroscopically
• May be self-donor, or cadaver
• Bone plugs inserted into tibia and femur
• Initial screw for stability, let nature do the
  rest
• Wolffs Law

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Osteoporosis slide presentation(Aging(?), OA and
OP)
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Click on logo for more information
World Health Organization
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The mechanical basis ofOsteoarthritis(Osteoarthr
osis)
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Osteoarthritis Slide Show
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Osteoarthritis Slide Show
Click on the info button to read on NSAIDs
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Role of Meniscii
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Meniscii effect on mechanical stress
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OA diseased joint
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Progression of joint degeneration
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Knee OA
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Arthritic Hip
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Arthritis in the hands
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OA and Aging

• Afflicts more persons than cardiovascular disease
• 37 million Americans have OA
• 5 at age 20
• 85 at age 65

Source thehealthpages.com
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And, of greater importance to many people, over
8,000,000 dogs.
Source www.pfizer.com
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Why is OA a problem?

• Pain
• During motion
• Night pain
• Limping
• energy cost
• Shifts stress other joints
• Limits ADLs of 35 over age 65
• Economic Cost
• Medical
• Time from work

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Factors Associated with OA

• Genetics
• Aging
• Gender
• Body weight
• Bone density
• Previous trauma

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Factors Associated with OA

• Genetics ?
• Aging
• Gender
• Body weight
• Bone density
• Previous trauma

Mechanical Stress
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OA is NOT an acute disease

• Few cases develop from an isolated joint trauma
  (secondary OA)

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2o OA Dr. Browns left (healthy) knee
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2o OA Dr. Browns right knee
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OA is NOT an acute disease

• Few cases develop from an isolated joint trauma
  (secondary OA)
• Most diagnosed as idiopathic (no identifiable
  cause)
• Eric Radin OA reflects the cumulative effect of
  pathological load bearing
• How the body deals with impulsive loading

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Impulsive Load
A load that reaches a relatively high magnitude
in a short period of time.

• Contact (impact) forces
• collisions

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Transmission Attenuation of Impact Force
(Impulsive Load)
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Impulsive Load
A load that reaches a relatively high magnitude
in a short period of time.

• Contact (impact) forces
• collisions
• Muscle force
• bursts of high force

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Bone Response to Stress

• Wolff's law (1892)
• tissue adapts to level of imposed stress
• increased stress
• hypertrophy (increase strength)
• decreased stress
• atrophy (decrease strength)
• SHAPE REFLECTS FUNCTION
• Genetics, Body weight, physical activity, diet,
  lifestyle (see note clippings)

(review the stress continuum)
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Mechanical model of initiation and progression of
OA
Impulse Loading Trabecular Microfracture Bone
remodeling Resultant Bone Stiffening Increased
stress on articular cartilage Cartilage
Degeneration Functional Incapacitation
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Mechanical model of initiation and progression of
OA
Impulse Loading Trabecular Microfracture Bone
remodeling Resultant Bone Stiffening Increased
stress on articular cartilage Cartilage
Degeneration Functional Incapacitation
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Mechanical model of initiation and progression of
OA
Impulse Loading Trabecular Microfracture Bone
remodeling Resultant Bone Stiffening Increased
stress on articular cartilage Cartilage
Degeneration Functional Incapacitation
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Q-angle
Implications for joint loading?
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Knee alignment effects on stress patterns
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Muscle relationship with OAQuadriceps example
Varus alignment Decreased QF efficiency Fatigue
Decreased shock absorption Increased load on
joint Increased risk of joint damage
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Muscle relationship with OAQuadriceps example
Varus alignment Decreased QF efficiency Fatigue
Decreased shock absorption Increased load on
joint Increased risk of joint damage
Fitness Level (age) Critical ability
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Pain effects on movement
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Possible interventions for pain
PAIN
Maintain Activity
Rest
MODIFIED ACTIVITY

• Modify equipment
• Modify task
• Modify environment

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Major Benefit of Exercise/Activity

• Improved sense of well-being
• Control over life
• Better future health
• Better sleep
• Better diet
• More energy

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Modify the environment
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Cane Use
Biomechanical rationale to hold cane in the hand
opposite to the injured side.
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Lifestyle Factors and the Prevention of
Osteporosis
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Bone Mineral Density
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BMD
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Bone strength depends on integrity of support
structures
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Healthy Vertebral Body
Note trabecular structure, density of cortical
bone
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Osteoporotic Vertebral Body
Note loss of trabecular integrity, thinning of
cortical bone
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Close up of trabecula
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OP effect on Diaphysis
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Why is OP a problem?
Decrease in bone strength Increased risk of
fracture (osteoporotic fracture)
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Osteoporosis and Stress/Strain
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Costs
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Treat the Symptoms Deal with it as an aesthetic
problem
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Total Hip Implants
Acetabular Component
Metal Shell
Polyethylene Liner
Head
Collar
Stem
Osteotomy Line
Femoral Component
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Traditional Approach to OP Intervene after
the disease becomes symptomatic Treat the
symptoms
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Prevention not Treatment
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Osteoporosis is basically an imbalance between
the rates of bone production and bone resorption
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OP as a balance of Osteoblasts and Osteoclasts
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Critical factors in development of OP

• Peak BMD
• Age of peak BMD
• Rate of loss of BMD

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Effect of Peak BMD on osteoporosis
BMD
Fracture Threshold
20
50
80
AGE (years)
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Effect of Peak BMD on osteoporosis
Menopause
BMD
Fracture Threshold
20
50
80
AGE (years)
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Effect of Peak BMD on osteoporosis
Typical peak BMD
BMD
Fracture Threshold
20
50
80
AGE (years)
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Effect of Peak BMD on osteoporosis
BMD
Low peak BMD
Fracture Threshold
20
50
80
AGE (years)
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Adolescence

• Critical years for
• Developing attitude
• fitness/lifestyle
• Increasing BMD

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Effect of Peak BMD on osteoporosis
High peak BMD
BMD
Fracture Threshold
20
50
80
AGE (years)
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Effect of attaining peak BMD at later age
Peak reached at typical age
Peak reached at later age
BMD
Fracture Threshold
20
50
80
AGE (years)
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Effect of Peak BMD on osteoporosis
Can the rate of BMD decrease be altered?
BMD
Fracture Threshold
20
50
80
AGE (years)
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Avoiding osteoporosis
High peak BMD reached at later age
Reduce loss rate
Typical BMD
BMD
Fracture Threshold
20
50
80
AGE (years)
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Bone Response to Stress

• Wolff's law (1892)
• tissue adapts to level of imposed stress
• increased stress
• hypertrophy (increase strength)
• decreased stress
• atrophy (decrease strength)
• SHAPE REFLECTS FUNCTION
• Genetics, Body weight, physical activity, diet,
  lifestyle (see note clippings)

(review the stress continuum)
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Measuring BMD

• Bone sample
• DEXA scan
• OsteoGram hand x-ray

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Recommended Calcium in Diet
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Effect of Asymmetrical Loading on BMD
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DEXA (Hologic QDR-4550) was used to perform the
bone scans.
Femoral Neck
Lumbar Spine