Chapter 9: Mechanisms and
Characteristics of
Musculoskeletal and Nerve
Trauma
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Mechanical Injury
• Trauma is defined as physical injury or
wound, produced by internal or external
force
• Mechanical injury results from force or
mechanical energy that changes state
of rest or uniform motion of matter
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• Tissue Properties
– Load
• An external force acting on the body causing
internal reactions within the tissues
– Stiffness
• Ability of a tissue to resist a load
• Greater stiffness = greater magnitude load can
resist
– Stress
• Internal resistance to a load
– Strain
• Internal change in tissue (i.e. length) resulting
in deformation
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Figure 9-1
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– Body tissues are viscoelastic and contain
both viscous and elastic properties
– Yield point
• Point at which elasticity is almost exceeded is
the yield point
• If deformation persists, following release of load
permanent or plastic changes result
• When yield point is far exceeded mechanical
failure occurs resulting in damage
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• Tissue Loading
– Tension
• Force that pulls and
stretches tissue
– Compression
• Force that results in
tissue crush – two
forces applied
towards one another
– Shearing
Figure 9-2
• Force that moves
across the parallel
organization of
tissue
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– Bending
• Two force pairs act at
opposite ends of a
structure (4 points)
• Three forces cause
bending (3 points)
• Already bowed structures
encounter axial loading
– Torsion
• Loads caused by twisting
in opposite directions
from opposite ends
• Shear stress
encountered will be
perpendicular and
parallel to the loads
Figure 9-2
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Traumatic vs. Overuse Injuries
• Nature of physical activity dictates that
over time injury will occur
• Debate over acute vs. chronic injuries
– When injury is acute – something has
initiated the injury process
– Injury becomes chronic when it doesn’t
properly heal
• Could define relative to mechanism
– Traumatic (i.e. a direct blow) vs. Overuse
(i.e. repetitive dynamic use over time)
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Musculotendinous Unit
Injuries
• High incidence in athletics
• Anatomical Characteristics
– Composed of contractile cells that produce
movement
– Possess following characteristics
•
•
•
•
Irritability
Contractility
Conductivity
Elasticity
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Skeletal Muscle
– Three types
of muscle
• Cardiac
• Smooth
• Striated
(skeletal)
Figure 9-3
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• Muscle Strains
– Stretch, tear or rip to muscle or adjacent
tissue
– Cause is often obscure
• Abnormal muscle contraction is the result of
1)failure in reciprocal coordination of agonist
and antagonist, 2) electrolyte imbalance due to
profuse sweating or 3) strength imbalance
– May range from minute separation of
connective tissue to complete tendinous
avulsion or muscle rupture
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– Muscle Strain Grades
• Grade I - some fibers have been stretched or
actually torn resulting in tenderness and pain
on active ROM, movement painful but full range
present
• Grade II - number of fibers have been torn and
active contraction is painful, usually a
depression or divot is palpable, some swelling
and discoloration result
• Grade III- Complete rupture of muscle or
musculotendinous junction, significant
impairment, with initially a great deal of pain
that diminishes due to nerve damage
– Pathologically, strain is very similar to
contusion or sprain with capillary or blood
vessel hemorrhage
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– Time required for healing may be lengthy
– Often involves large, force-producing
muscles
– Treatment and recovery may take 6-8
weeks depending on severity
– Return to play too soon could result in reinjury
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•
Muscle Cramps
–
–
–
•
Painful involuntary skeletal muscle
contraction
Occurs in well-developed individuals when
muscle is in shortened position
Experienced at night or at rest
Muscle Guarding
–
–
Following injury, muscles within an effected
area contract to splint the area in an effort to
minimize pain through limitation of motion
Involuntary muscle contraction in response
to pain following injury
•
Not spasm which would indicate increased
tone due to upper motor neuron lesion in the
brain
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• Muscle Spasms
– A reflex reaction caused by trauma
– Two types
• Clonic - alternating involuntary muscular
contractions and relaxations in quick
succession
• Tonic - rigid contraction that lasts a period of
time
– May lead to muscle or tendon injuries
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•
Muscle Soreness
–
–
–
Overexertion in strenuous exercise resulting in
muscular pain
Generally occurs following participation in
activity that individual is unaccustomed
Two types of soreness
1) Acute-onset muscle soreness - accompanies fatigue,
and is transient muscle pain experienced immediately
after exercise
2) Delayed-onset muscle soreness (DOMS) - pain that
occurs 24-48 hours following activity that gradually
subsides (pain free 3-4 days later)
– Potentially caused by slight microtrauma to muscle or
connective tissue structures
–
Prevent soreness through gradual build-up of
intensity
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• Tendon Injuries
– Wavy parallel collagenous fibers organized
in bundles - upon loading
• Can produce and maintain 8,700- 18,000
lbs/in2
• Collagen straightens during loading but will
return to shape after loading
– Breaking point occurs at 6-8% of increased
length
– Tears generally occur in muscle and not
tendon
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– Repetitive stress on tendon will result in
microtrauma and elongation, causing
fibroblasts influx and increased collagen
production
• Repeated microtrauma may evolve into chronic
muscle strain due to reabsorption of collagen
fibers
• Results in weakening tendons
• Collagen reabsorption occurs in early period of
sports conditioning and immobilization making
tissue susceptibility to injury – requires gradual
loading and conditioning
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• Tendinitis
– Gradual onset, with diffuse
tenderness due to repeated
microtrauma and degenerative
changes
– Obvious signs of swelling and pain
– Key to treatment is rest
– May require substitution of activity
in order to maintain fitness without
stressing injured structure
– Without proper healing condition
may begin to degenerate and be
referred to as tendinosis
• Less inflammation, more visibly
swollen with stiffness and restricted
motion
• Treatment involves stretching and
strengthening
Figure 9-5
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• Tenosynovitis
– Inflammation of synovial sheath
– In acute case - rapid onset, crepitus, and
diffuse swelling
– Chronic cases result in thickening of
tendon with pain and crepitus
– Often occurs in long flexor tendon of the
digits and the biceps tendon
– Due to nature of injury anti-inflammatory
agents may be helpful
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• Myofascial Trigger Points
– Discrete, hypersensitive nodule within tight
band of muscle or fascia
– Classified as latent or active
– Develop as the result of mechanical stress
• Either acute trauma or microtrauma
• May lead to development of stress on muscle
fiber = formation of trigger points
– Latent trigger point
• Does not cause spontaneous pain
• May restrict movement or cause muscle
weakness
• Become aware of presence when pressure is
applied
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– Active trigger point
•
•
•
•
•
Causes pain at rest
Applying pressure = pain = jump sign
Tender to palpation with referred pain
Tender point vs. trigger point
Found most commonly in muscles involved in
postural support
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• Contusions
– Result of sudden blow to body
– Can be both deep and superficial
– Hematoma results from blood and lymph
flow into surrounding tissue
• Localization of extravasated blood into clot,
encapsulated by connective tissue
• Speed of healing dependent on the extent of
damage
– Chronically inflamed and contused tissue
may result in generation of calcium
deposits (myositis ossificans)
• Prevention through protection of contused area
with padding
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• Atrophy and Contracture
– Atrophy is wasting away of muscle due to
immobilization, inactivity, or loss of nerve
functioning
– Contracture is an abnormal shortening of
muscle where there is a great deal of
resistance to passive stretch
• Generally the result of a muscle injury which
impacts the joint, resulting in accumulation of
scar tissue
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Synovial Joints Injuries
• Each joint has both hyaline or articular
cartilage and a fibrous connective tissue
capsule
• Additional synovial joint characteristics
– Capsule and ligaments for support
– Capsule is lined with synovial membrane
– Hyaline cartilage
– Joint cavity with synovial fluid
– Blood and nerve supply with muscles
crossing joint
– Menisci (fibrocartilage)© 2011 McGraw-Hill Higher Education. All rights reserved.
Figure 9-8
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• Ligament Sprains
– Result of traumatic joint twist that causes
stretching or tearing of connective tissue
– Graded based on the severity of injury
• Grade I - some pain, minimal loss of function, no
abnormal motion, and mild point tenderness
• Grade II - pain, moderate loss of function, swelling,
and instability with tearing and separation of
ligament fibers
• Grade III - extremely painful, inevitable loss of
function, severe instability and swelling, and may
also represent subluxation
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• Can result in joint effusion and swelling,
local temperature increase, pain and
point tenderness, ecchymosis (change
in skin color) and possibly an avulsion
fracture
• Greatest difficulty with grade 1 & 2
sprains is restoring stability due to
stretched tissue and inelastic scar tissue
which forms
• To regain joint stability strengthening of
muscles around the joint is critical
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• Dislocations and Subluxations
– Result in separation of bony articulating
surfaces
– Subluxation
• Partial dislocations causing incomplete
separation of two bones
• Bones come back together in alignment
– Dislocations
• High level of incidence in fingers and shoulder
• Occurs when at least one bone in a joint is
forced out of alignment and must be manually
or surgically reduced
• Gross deformity is typically apparent with
bilateral comparison revealing asymmetry
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– Dislocation (cont.)
• Stabilizing structures of the joint
are disrupted
• Joint often becomes susceptible
to subsequent dislocations
• X-ray is the only absolute
diagnostic technique (able to see
bone fragments from possible
avulsion fractures, disruption of
growth plates or connective
tissue)
• Dislocations (particularly first
time) should always be
considered and treated as a
fracture until ruled out
• “Once a dislocation, always a
dislocation”
Figure 9-9
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• Osteoarthritis
– Wearing away of hyaline
cartilage as a result of normal
use
– Changes in joint mechanics lead
to joint degeneration
– Commonly affects weight
bearing joints but can also
impact shoulders and cervical
spine
– Symptoms include pain (as the
result of friction), stiffness,
prominent morning pain,
localized tenderness, creaking,
grating
– Either generalized joint pain or
localized to one side of the joint
Figure 9-10
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– Bursitis
• Bursa are fluid filled sacs
that develop in areas of
friction
• Sudden irritation can cause
acute bursitis, while overuse
and constant external
compression can cause
chronic bursitis
• Signs and symptoms
include swelling, pain, and
some loss of function
• Repeated trauma can lead
to calcification and
degeneration of internal
bursa linings
Figure 9-11
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– Capsulitis and Synovitis
• Capsulitis is the result of repeated joint trauma
• Synovitis can occur acutely but will also
develop following mistreatment of joint injury
• Chronic synovitis can result in edema,
thickening of the synovial lining, exudation can
occur and a fibrous underlying develops
• Motion may become restricted and joint noises
may develop
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Bone Injuries
• Anatomical
Characteristics
– Dense connective
tissue matrix
– Outer compact tissue
– Inner porous
cancellous bone
including Haversian
canals
Figure 9-12
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– Bone Functions
•
•
•
•
•
Body support
Organ protection
Movement (through joints and levers)
Calcium storage
Formation of blood cells (hematopoiesis)
– Types of Bone
•
•
•
•
•
Classified according to shape
Flat bones - skull, ribs, scapulae
Irregular bones - vertebrae and skull
Short bones- wrist and ankle
Long bones (humerus, ulna, tibia, radius, fibula,
femur) - bones most commonly injured
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– Gross Structures
• Diaphysis -shaft - hollow and cylindrical
- covered by compact bone
- medullary cavity contains yellow
marrow and lined by endosteum
• Epiphysis - composed of cancellous bone and
has hyaline cartilage covering
- provides areas for muscle
attachment
• Periosteum - dense, white fibrous covering
which penetrates bone via
Sharpey’ fibers
- contains blood vessels and
osteoblasts
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– Bone Growth
• Ossification occurs from synthesis of bones
organic matrix (work of osteoblasts and
osteoclasts)
• Involves growth of diaphysis and the epiphyseal
growth plates (towards one another)
• As cartilage matures, immature osteoblasts
replace to ultimately form solid bone
• Deforming forces, premature injury and growth
plate dislocation can alter growth patterns and/or
result in deformity of bone
• Bone diameter increases via the activity of
osteoblasts adding to the exterior while osteoclasts
break down bone in medullary cavity
• At full size, bone maintains state of balance
between osteoblastic and -clastic activity
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• Changes in activity and hormonal levels can
alter balance
• Bone loss begins to exceed external bone
growth overtime
• As thickness decreases, bones are less
resistant to forces --osteoporosis
• Bone’s functional adaptation to stresses follows
Wolff’s Law --every change in form and function
or in its function alone is followed by changes in
architectural design
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• Bone Fractures
– Classified as either closed or open
• Closed fractures are those where there is little
movement or displacement
• Open fractures involve displacement of the
fractured ends and breaking through the
surrounding tissue
– Serious condition if not managed properly
– Signs & symptoms
• Deformity, pain, point tenderness, swelling,
pain on active and passive movements
• Possible crepitus
• X-ray will be necessary for definitive diagnosis
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– Mechanism of Injury
• Fracture may be direct (at point of force application) or
indirect
• Sudden violent and forceful muscle contraction
– Types of fractures
•
•
•
•
•
•
•
•
Greenstick
Comminuted
Linear
Transverse
Oblique
Spiral
Impacted
Depressed
Figure 9-13
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– Less common types of fractures
• Avulsion
– Separation of bone fragment from cortex via pull of
ligament or tendon
•
•
•
•
Blowout fracture
Serrated fracture
Depressed fracture
Contrecoup fracture
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– Bone Strength & Shape
• Strength of bone can be impacted by changes
in shape and direction
– Long bones with gradual changes are less prone to
injury
• Cylindrical and hollow nature of bones make
them very strong - resistant to bending and
twisting
– Bone Loading Characteristics
• Bones can be stressed or loaded to failure by
tension, compression, bending, twisting and
shearing
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– Long Bone Load Characteristics (cont.)
• Either occur singularly or in combination
• Amount of load also impacts the nature of the
fracture
• More force results in a more complex fracture
• While force goes into fracturing the bone, some
energy and force is also absorbed by adjacent soft
tissues
• Bone has elastic properties allowing it to bend
• Typically brittle and a poor shock absorber
– Brittleness increases under tension forces, more so than
under compression
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– Stress fractures
• No specific cause but with a number of possible causes
– Overload due to muscle contraction, altered stress
distribution due to muscle fatigue, changes in surface,
rhythmic repetitive stress vibrations
• Bone becomes susceptible early in training due to
increased muscular forces and initial remodeling and
resorption of bone
• Progression involves, focal microfractures, periosteal or
endosteal response (stress fx) linear fractures and
displaced fractures
• Early detection is difficult, bone scan is useful, x-ray is
effective after several weeks
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• Typical causes include
–
–
–
–
–
Coming back to competition too soon after injury
Changing events without proper conditioning
Starting initial training too quickly
Changing training habits (surfaces, shoes….etc)
Variety of postural and foot conditions
• Signs and symptoms
– Focal tenderness and pain, (early stages)
– Pain with activity, (later stages) with pain becoming
constant and more intense, particularly at night, (exhibit
a positive percussion tap test)
• Common sites involve tibia, fibula, metatarsal shaft,
calcaneus, femur, pars interarticularis, ribs, and
humerus
• Management varies between individuals, injury site
and extent of injury
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– Epiphyseal Conditions
• Three types can be sustained by adolescents
(injury to growth plate, articular epiphysis, and
apophyseal injuries)
– Occur most often in children ages 10-16 years old
• Classified by Salter-Harris into five types (see
illustration on next slide)
– Apophyseal Injuries
• Young physically active individuals are
susceptible
– Apophyses are traction epiphyses in contrast to
pressure epiphyses.
– Serve as sites of origin and insertion for muscles
– Common avulsion conditions include Sever’s disease
and Osgood-Schlatter’s disease
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Figure 9-15
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– Osteochondrosis
• Also known as osteochondritis dissecans and
apophysitis (if located at a tubercle/tuberosity)
• Causes not well understood
• Degenerative changes to epiphyses of bone
during rapid child growth
• Possible cause includes 1)aseptic necrosis
(disrupted circulation to epiphysis, 2) fractures
in cartilage causing fissures to subchondral
bone, 3) trauma to a joint that results in
cartilage fragmentation resulting in swelling,
pain and locking
• With the apophysis, an avulsion fracture may
be involved, including pain, swelling and
disability
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Nerve Trauma
• Abnormal nerve responses can be
attributed to injury or athletic
participation
• The most frequent injury is neuropraxia
produced by direct trauma
• Lacerations of nerves as well as
compression of nerves as a result of
fractures and dislocations can impact
nerve function
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• Anatomical Characteristics
– Provides sensitivity and communication
from the CNS to muscles, sense organs
and various systems in the periphery
– Neuron cell body has a large nucleus with
branched dendrites which respond to
neurotransmitter substances
– Each nerve cell has an axon that conducts
nerve impulse
– Axons are encased in neurilemmal sheaths
(Schwann and satellite cells)
– Various neurological cells in CNS help to
form framework for nervous tissue
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• Nerve Injuries
– Compression and tension are primary
mechanisms
– May be acute or chronic
– Physical trauma causes pain and can result in a
host of sensory responses (pinch, burn, tingle,
muscle weakness, radiating pain)
– Long term problems can go from minor nerve
problems to paralysis
– Neuropraxia
•
•
•
•
Interruption in conduction through nerve fiber
Brought about via compression or blunt trauma
Impact motor more than sensory function
Temporary loss of function
– Pain can be referred as well
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Body Mechanics and Injury
Susceptibility
• Body moves very effectively in upright
position - able to overcome great forces
even with inefficient lever system
• Body must overcome inertia, muscle
viscosity and unfavorable angles of pull
• Mechanical reasons for injury - hereditary,
congenital, or acquired defects may
predispose athlete to injury
• Body build, structural make-up, habitual
incorrect application of skill may also
predispose individual to injury
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• Microtrauma and Overuse Syndrome
– Injuries as a result of abnormal and repetitive
stress and microtraumas fall into a class with
certain identifiable syndromes
– Frequently result in limitation or curtailment of
sports involvement
– Often seen in running, jumping, and throwing
activities
– Some of these injuries while small can be
debilitating
– Repetitive overuse and stress injuries include
• Achilles tendinitis, shin splints, stress fx, OsgoodSchlatter's disease, runner’s and jumper’s knee,
patellar chondromalacia and apophyseal avulsion
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• Postural Deviations
– Often an underlying cause of injury
– May be the result of unilateral muscle or bony and
soft tissue asymmetries
– Sports activities may cause asymmetries to
develop
– Results in poor pathomechanics
– Imbalance is manifested by postural deviations as
body tries to regain balance relative to CoG
• May be primary cause of injury
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– Injury generally becomes chronic and
athletic participation must stop
– Athletic trainer should attempt to correct
postural conditions
– Postural conditions can make individual
exceedingly more prone to injury
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