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Chapter 15. Understanding the Mechanics of Injury. Stress. Controlling the level of imposed stress is important in training various tissues and avoiding injury. Stress Continuum (Fig 15.3, 343). Distress (Causes malfunction) Pathologic underload zone Pathologic overload zone

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chapter 15

Chapter 15

Understanding the Mechanics of Injury

stress
Stress
  • Controlling the level of imposed stress is important in training various tissues and avoiding injury.
stress continuum fig 15 3 343
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
slide4
Distress

Eustress

Eustress

Distress

Phys Overload

Path Overload

Path Underload

Phys Load

relationship of magnitude and frequency to type of injury fig 15 5
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)
slide6
Repetitive loading
    • repeated application of a subacute stress that is usually of low magnitude (Microtrauma)
injury acute definition cdc
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.

three major categories of injury
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.

preventing overuse injury in young pitchers controversy
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

types of fractures
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
slide17
Avulsion fracture of

the patella

following B-PT-B

repair of the

ispsilateral ACL

comminuted fracture
Comminuted Fracture

Low Energy

High Energy

types of fractures1
Types of Fractures

What is the error?

three biological phases to fracture healing
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
three biological phases to fracture healing1
Three Biological Phases to fracture healing
  • Inflammatory Phase
  • Reparative Phase (bony union)
    • about one month
    • callus formation
      • provisional ==> bony
three biological phases to fracture healing2
Three Biological Phases to fracture healing
  • Inflammatory Phase
  • Reparative Phase (bony union)
  • Remodelling Phase
    • restoration of original contour
changes in acl surgery
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
changes in acl surgery1
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
    • Wolff’s Law
slide28
The

mechanical

basis ofOsteoarthritis(Osteoarthrosis)

oa and aging
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

why is oa a problem
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
factors associated with oa
Factors Associated with OA
  • Genetics
  • Aging
  • Gender
  • Body weight
  • Bone density
  • Previous trauma
factors associated with oa1
Factors Associated with OA
  • Genetics ?
  • Aging
  • Gender
  • Body weight
  • Bone density
  • Previous trauma

Mechanical

Stress

oa is not an acute disease
OA is NOTan acute disease
  • Few cases develop from an isolated joint trauma (secondary OA)
oa is not an acute disease1
OA is NOTan 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
impulsive load
Impulsive Load

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

  • Contact (impact) forces
    • collisions
slide48
Transmission

&

Attenuation

of

Impact Force (Impulsive Load)

impulsive load1
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
bone response to stress
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)

mechanical model of initiation and progression of oa
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

mechanical model of initiation and progression of oa1
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

mechanical model of initiation and progression of oa2
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

q angle
Q-angle

Implications for joint loading?

muscle relationship with oa quadriceps example
Muscle relationship with OAQuadriceps example

Varus alignment

Decreased QF efficiency

Fatigue

Decreased shock absorption

Increased load on joint

Increased risk of joint damage

muscle relationship with oa quadriceps example1
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

possible interventions for pain
Possible interventions for pain

PAIN

Maintain

Activity

Rest

MODIFIED

ACTIVITY

  • Modify equipment
  • Modify task
  • Modify environment
major benefit of exercise activity
Major Benefit of Exercise/Activity

Improved sense of well-being

  • Control over life
  • Better future health
  • Better sleep
  • Better diet
  • More energy
cane use
Cane Use

Biomechanical rationale to hold cane in the hand opposite to the injured side.

slide65
Bone

Mineral

Density

healthy vertebral body
Healthy Vertebral Body

Note: trabecular structure, density of cortical bone

osteoporotic vertebral body
Osteoporotic Vertebral Body

Note: loss of trabecular integrity, thinning of cortical bone

why is op a problem
Why is OP a problem?

Decrease in bone strength

Increased risk of fracture

(osteoporotic fracture)

slide80
Treat the Symptoms

Deal with it as

an aesthetic problem

slide82
Total Hip Implants

Acetabular Component

Metal

Shell

Polyethylene

Liner

Head

“Collar”

Stem

Osteotomy

Line

Femoral Component

slide85
Traditional Approach

to OP

Intervene after

the disease becomes

symptomatic

Treat the symptoms

slide86
Prevention

not

Treatment

critical factors in development of op
Critical factors in development of OP
  • Peak BMD
  • Age of peak BMD
  • Rate of loss of BMD
slide90
Effect of Peak BMD on osteoporosis

BMD

Fracture Threshold

20

50

80

AGE (years)

slide91
Effect of Peak BMD on osteoporosis

Menopause

BMD

Fracture Threshold

20

50

80

AGE (years)

slide92
Effect of Peak BMD on osteoporosis

Typical peak BMD

BMD

Fracture Threshold

20

50

80

AGE (years)

slide93
Effect of Peak BMD on osteoporosis

BMD

Low peak BMD

Fracture Threshold

20

50

80

AGE (years)

adolescence
Adolescence
  • Critical years for
    • Developing attitude
      • fitness/lifestyle
    • Increasing BMD
slide95
Effect of Peak BMD on osteoporosis

High peak BMD

BMD

Fracture Threshold

20

50

80

AGE (years)

slide96
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)

slide97
Effect of Peak BMD on osteoporosis

Can the rate

of BMD decrease

be altered?

BMD

Fracture Threshold

20

50

80

AGE (years)

slide98
Avoiding osteoporosis

High peak BMD reached at later age

Reduce

loss rate

Typical BMD

BMD

Fracture Threshold

20

50

80

AGE (years)

bone response to stress1
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)

measuring bmd
Measuring BMD
  • Bone sample
  • DEXA scan
  • OsteoGram: hand x-ray
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