Chapter 4
Injury Mechanism and
Classification of Injury
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Anatomic Foundations
• Anatomic position
Anatomic position
• Joint movement
– Sagittal plane
– Frontal plane
– Transverse plane
• Directional terms
• Movement Terms
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Mechanism of Injury
• Mechanism of Injury (MOI): How an injury occurs
• Components used to analyze MOI:
– Application of force
– Tissue type
• Severity of force
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Force
• Force: a push or pull acting on a body (e.g., gravity,
friction)
• Force acting on a body causes:
– Acceleration
– Deformation
• Factors that determine injury:
– Magnitude of force
– Material properties of tissues involved
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Force (cont’d)
• Small load = elastic response
• Large load = plastic response
• Yield point = load exceeds the ultimate failure point
of the tissue resulting in mechanical failure
• Anisotropic = material is stronger in resisting force
from certain directions than others
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Mechanical Forces - Injury
• Compression
Mechanisms of injury
– Force that crushes
tissues
• Tension
– Force that pulls and
stretches tissues
• Shearing
– Force that moves
across the parallel
design of the fibers
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Stress
• Stress = Force x Surface area affected
• Same force over a large area vs. a small area can
have very different results
Stress
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Injury Types
• Acute Injury
– Single force
– Characterized by a definitive moment of onset
– Force = macrotrauma
• Chronic Injury
– Repeated forces
– Characterized by becoming more problematic over
time (Gradual onset over time)
– Forces = microtrauma
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Check for Understanding!
Movements in the sagittal plane include flexion, extension,
abduction, and adduction.
A. True
B. False
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Check for Understanding!
Which of the following is a correctly matched pair of terms?
(Select all that apply)
A. Adduction – movement away from the midline of the
body
B. Flexion – decreasing an angle
C. Extension – increasing an angle
D. Plantar flexion – movement of the forefoot toward the
shin
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Check for Understanding!
When tissues sustain a force, what are the primary factors
that determine the occurrence of an injury? (Select all
that apply)
A. The magnitude of the force
B. The direction of the force
C. The material properties of the involved tissues
D. The length of time the force is applied
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Check for Understanding!
What are the three primary mechanical forces
that produce injury?
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Anatomical Properties of Soft Tissue
• Collagen
– Primary component of skin, tendon, ligaments
– Protein substance strong in resisting tensile
forces
– Wavy configuration that allows for an elastic
type deformation or stretch but, otherwise, is
inelastic
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Anatomical Properties of Soft Tissue
(cont’d)
Collagen fibers
• Elastin
– Protein substance in
connective tissue
– Adds elasticity
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Skin
• Epidermis
– Multiple layers
• Dermis
– Loose,
multidirectional
arrangement of
collagen fibers
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Skin Injury Classification
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Skin Wounds
• Blisters
– Accumulation of fluid between epidermis and
dermis
– Caused by repeated application of shear in one
or more directions
• Skin bruises
– Accumulation of blood within skin
– Results from compression sustained during a
blow
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Muscles
• Produce skeletal
movement and maintain
postural alignment
• Viscoelastic
– Extensibility
– Elasticity
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Muscle tissue
Muscle (cont’d)
• Irritability: ability to respond to a stimulus
– Electrochemical – nerve impulse
– Mechanical – external blow
• Contractility: ability to develop tension
– Isometric
– Concentric
– Eccentric
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Tendons
• Muscle to bone
• Dense connective tissue with unidirectional bundles
of collagen & some elastin
• Collagen – parallel arrangement
– Helps in resisting high, unidirectional tension
loads from the attached muscle
• 2X as strong as muscle it serves
• Yield point 5-8% in length
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Tendons (cont’d)
Collagen arrangements in tendon and ligament tissue
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Contusions
• MOI: compression
• Can be both deep and
superficial
• Must be cautious and
aware of more severe
injuries associated with
repeated blows
• S&S:
– Onset - acute
– Ecchymosis: if
superficial
– Hematoma
– Restrictions in ROM
– Pain – localized
– Swelling
– Associated nerve
compression
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Classification for Contusions
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Strains
• Damage to muscle or tendon
– Key factor: magnitude of force and structure's
cross-sectional area
• MOI:
– Abnormally high tensile force
• Most common site for tears: near the
musculotendinous junction
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Classification of Strains
<table 4.4, classifications of strains>
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Muscle Cramps and Spasms
• Involuntary muscle contraction
• Cramp:
– Biochemical imbalance (dehydration) associated
with muscle fatigue
– Painful
– Types
• Clonic – alternating contraction/relaxation
• Tonic – constant
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Muscle Cramps and Spasms (cont’d)
• Spasm:
– Reflex action caused by:
• Biochemical imbalance or
• Mechanical blow to nerve or muscle
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Myositis and Fasciitis
• MOI: repeated movements irritate the tissues
• Myositis:
– Inflammation of muscle tissue (e.g., shin
splints)
• Fasciitis:
– Inflammation of the fascia (e.g., plantar
fasciitis)
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Tendinitis and Tenosynovitis
• Tendinitis: inflammation of a tendon
– Related to aging and degenerative changes
– S&S: pain and swelling with tendon movement
• Tenosynovitis: inflammation of the tendon sheath
– Acute: rapid onset, crepitus, local swelling
– Chronic: same as acute, thickened tendon,
nodule formation in sheath
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Myositis Ossificans
• Mineral deposits in muscle associated with
prolonged chronic inflammation
– Ectopic calcification
– Common site: quadriceps
• Calcific tendinitis: mineral deposits in the tendon
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Overuse Injuries
• Results from repetitive use
• Factors:
– Intrinsic
– Extrinsic
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Overuse Injuries (cont’d)
• Classification
– Stage 1: pain after activity only
– Stage 2: pain during activity, does not restrict
performance
– Stage 3: pain during activity, restricts
performance
– Stage 4: chronic unremitting pain, even at rest
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Anatomical Considerations of Joints
• Articulation of two bones
• Classified by structure and function
• Structure
– Cartilaginous
– Fibrous
– Synovial
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Anatomical Considerations of Joints
(cont’d)
• Function: based on the amount of movement
allowed
– Synarthoses
– Amphiarthroses
– Diarthroses
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Diarthrodial Joints
• Components
– Articular cartilage
– Joint (synovial) cavity
– Articular capsule
– Synovial fluid
– Reinforcing ligaments
• Intrinsic or Extrinsic
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Diarthrodial Joints (cont’d)
Joint components
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Articular Cartilage
• Ends of bones covered by hyaline cartilage…solid
type of connective tissue
• More resistant to deformation than fibrous
connective tissue and more resilient than bone
• No blood supply; nourished by synovial fluid
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Joint Cavity
• Filled with synovial fluid
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Articular Capsule
• Cuff of fibrous tissue
– Primarily bundles of collagen
• Primary function: hold bones together
• Inner layer: synovial membrane
– Produces synovial fluid that lubricates the joint.
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Synovial Fluid
• Functions
– Lubricate joint
– Reduce friction
– Nourish joint
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Ligaments
• Bone to bone
– Intrinsic
– Extrinsic
• Maintain anatomical integrity and structural
alignment
• Collagen and elastin intermixed (contain elastin –
more elastic than tendons)
– Viscoelastic
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Ligaments (cont’d)
• Resists large tensile loads along the long axis of the
ligament and smaller loads from other directions –
static stabilizers
• Fail in fast loading situations
• Strongest in their middle and weakest at their ends
• Healing process – slow due to a limited blood supply
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Classification of Diarthrodial Joints
• Plane
• Condyloid
• Hinge
• Saddle
• Pivot
• Ball-and-socket
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Injury to the Ligament
• Compromises the ability of the ligament to stabilize
the joint
• MOI:
– High tensile force
• S&S:
– Pain; point tenderness; swelling; loss of
function; instability
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Classification of Sprains
<table 4.5, classification of sprains>
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Dislocations and Subluxations
• Joint forced beyond
normal limits
• MOI: tension
• Increased susceptibility
for chronic or recurrent
dislocations
• S&S:
– Pain
– Swelling
– Point tenderness
– Deformity
– Loss of limb
function
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Osteoarthritis
• Degeneration of articular cartilage
• S&S:
– Pain
– Limited movement
• No definitive cause; rather, several contributing
factors
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Bursitis
• Inflammation of bursa
• S&S:
• Acute or chronic
– Localized swelling
• MOI:
– Point tenderness
– Compression
– Warm to touch
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Soft Tissue Injury
Check for Understanding!
The discoloration or swelling outside a joint in the
surrounding soft tissue is termed:
A. Bruising
B. Ecchymosis
C. Edema
D. Effusion
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Soft Tissue Injury
Check for Understanding!
The ability of a muscle to be stretched or increased in
length is termed:
A. Contractility
B. Elasticity
C. Plasticity
D. Extensibility
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Soft Tissue Injury
Check for Understanding!
Joint capsules are fluid-filled sacs that serve to reduce
friction in the tissues surrounding the joints.
A. True
B. False
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Soft Tissue Injury
Check for Understanding!
Which of the following statements is true? (Select all that
apply)
A. A tear of a ligament is referred to as a sprain.
B. A muscle spasm is brought on by a biochemical
imbalance, sometimes associated with muscle fatigue.
C. Overuse injuries are more often attributed to intrinsic
rather than extrinsic factors.
D. The onset of bursitis can be acute or chronic.
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Soft Tissue Injury
Check for Understanding!
Strains and sprains that produce moderate
discomfort, tenderness, swelling, ecchymosis,
detectable joint instability, and/or muscle weakness
are categorized as:
A. 1st degree
B. 2nd degree
C. 3rd degree
D. Severe
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Anatomical Properties of Bone
• Primary constituents:
– Calcium carbonate
– Calcium phosphate
– Collagen
– Water
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Anatomical Properties of Bone (cont’d)
Bone macrostructure
• Structure:
– Diaphysis
– Epiphysis
– Membranes
• Periosteum
– Medullary cavity
– Apophysis
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Anatomical Properties of Bone (cont’d)
• Bone growth:
– Longitudinal
• Continues until epiphysis closes
– Diameter
• Continues to grow throughout life
– New bone formed via the periosteum; bone is
resorbed around the medullary cavity
• Osteoblasts: form new bone
• Osteoclasts: resorb bone
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Anatomical Properties of Bone (cont’d)
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Anatomical properties of Bone (cont’d)
• Composition
– Cortical
• Compact bone tissue of high density (low porosity)
• Outside
• Can withstand greater stress but less strain
– Cancellous
• Bone tissue of low density (high porosity)
• Inside
• Can tolerate more strain
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Bone Injury Classifications
Bone injury mechanisms
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Bone Injury Classifications (cont’d)
• Fracture: Disruption in the continuity of bone
• S&S:
– Rapid swelling
– Ecchymosis
– Deformity or shortening of the limb
– Precise point tenderness
– Grating or crepitus
– Guarding or disability
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Bone Injury Classifications (cont’d)
• Type of fracture dependent upon:
– Force applied
– The health and maturity of the bone at the time
of injury
• Bone susceptible to:
– Compression, tension, shear, bending, and
torsion
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Types of Fractures
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Stress Fracture
• MOI: repeated lower magnitude forces
• Can become worse over time
• Begins as a small disruption in the outer layers of
cortical bone and ending as complete cortical
fracture with possible displacement
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Osteopenia
• Reduced bone mineral density
• Predisposes individual to fracture
– Particularly stress fractures
• Possible causes:
– Amenorrhea, hormonal factors, dietary
insufficiencies
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Classification of Epiphyseal Injuries
• Classifications
– Injury to growth plate could result in alteration
in normal growth
– Acute injury
Epiphyseal injuries
• Types I-V
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Classification of Epiphyseal Injuries
(cont’d)
• Osteochondrosis
– Disruption of blood supply to epiphysis
– Idiopathic
– Causing necrosis and possible deformity
– Example: Legg-Calvé-Perthes disease
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Classification of Epiphyseal Injuries
(cont’d)
• Apophysitis
– Osteochondrosis of apophysis
– Idiopathic or traumatic avulsion fracture
– Example:
• Sever’s disease
• Osgood-Schlatter disease
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Bone Tissue Injury
Check for Understanding!
In a comminuted fracture, the bone fragments into
several pieces.
A. True
B. False
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Bone Tissue Injury
Check for Understanding!
Osteopenia is a condition:
A. That is exclusive to an older adult population
B. That predisposes an individual to stress fractures
C. That only involves females
D. That inhibits longitudinal bone growth
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Bone Tissue Injury
Check for Understanding!
Epiphyseal injuries can include damage to the: (select all
that apply)
A. Epiphyseal plate
B. Ligaments
C. Articular cartilage
D. The apophysis
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Anatomical Properties of Nerves
• Nervous System
– CNS:
• Brain
• Spinal cord
– PNS:
• 12 pairs of cranial nerves
• 31 pairs of spinal nerves, along with their
branches
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Anatomical Properties of Nerves (cont’d)
Spinal nerves
• Spinal nerves
– Roots
• Posterior –
afferent
• Anterior –
efferent
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Nerve Injury Classifications
• MOI: Tensile or compression force
• Neurapraxia (grade 1)
– Localized conduction block: temporary loss of
sensation and/or motor
– Resolves within days to a few weeks
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Nerve Injury Classifications (cont’d)
• Axonotmesis (grade 2)
– Significant motor and mild sensory deficits
– Lasts at least 2 weeks
• Neurotmesis (grade 3)
– Motor and sensory deficit
– Lasts up to 1 year
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Nerve Injury Classifications (cont’d)
• Compression:
– More complex; dependent upon:
• Force magnitude and duration
• Direct or indirect
• Nerve injuries result in a variety of afferent symptoms
– Hyperesthesia
– Hypoesthesia
– Paresthesia
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Nerve Injury Classifications (cont’d)
• Neuralgia
– Chronic pain along nerve course
• Healing: if completely severed, healing does not
occur
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The Neurological Basis of Pain
• Sources
– Somatic, visceral, and psychogenic
• Nociceptors: produce pain sensation
– Mechanosensitive: initiate pain by acute trauma
– Chemosensitive: causes persistent pain in
chronic injuries and the early stages of healing
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The Neurological Basis of Pain (cont’d)
• Fibers transmitting pain
– A fibers
– C fibers
– T cells
• Gate control theory of pain
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The Neurological Basis of Pain (cont’d)
• Factors than mediate pain
– Brain production of opioid peptides and endorphins
– Cognitive and affective filters
• Referred pain
– Pain perceived at a location remote from the site
actually causing the pain
• Radiating pain
– Pain felt both at its source and along a nerve
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Bone Tissue Injury
Check for Understanding!
The posterior branches are the afferent (sensory)
nerves that transmit information from sensory
receptors in the skin, tendons, ligaments, and
muscles to the central nervous system.
A. True
B. False
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Bone Tissue Injury
Check for Understanding!
___________ is perceived at a location remote from
the site of the tissues actually causing the pain.
A. Radiating pain
B. Cognitive pain
C. Acute pain
D. Referred pain
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Bone Tissue Injury
Check for Understanding!
Grade II nerve injuries that produce significant motor
and mild sensory deficits that last at least two
weeks are termed:
A. Neurapraxia
B. Axonotmesis
C. Neurotmesis
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