3-Pathofysiology fx Flashcards
Organic, inorganic and water components of the bone in %
35% organic
45% inorganic
25% water
What is the major inorganix component?
crystalline hydroxapatite
Organic matrix is compromised of collagen type (mention)
Type I (>90% or organic component)
Type I collagen is responsible for which proprietires of the bone?
viscoelastic properties
Mineralization confers 2 proprieties
strength and stiffness
The collagen phase contributes to
ductility and overall toughness
Harvesian systems are present in compact bone to provide what?
Vascularization to osteocytes embeddedin bone matrix
Concentric lamellae that surround a central blood vessel in Haversian canals makeup the osteons of the Haversian system in which type of bone?
compact bone
During bone formation and growth the first cells to be laid down are
Primary osteons
During postnatal growth the long bone diameter is achieved through ______ formation
periosteal formation of woven bone that provides the structure for the formation of primary osteons or circumferential lamellae
Cement lines are formed by (type of cell)
osteoblasts at the time of transition from bone resorption to formation
Biomechanical response of bone to loading is dependent on its geometry and
material composition
Define the loading characteristics
Direction, rate, magnitude, frequency, duration
Transverse cracking, where the crack must course
through longitudinally oriented osteons is thougher or lighter than longitudinal cracking?
tougher than longitudinal cracking, where the crack splits osteons along the longitudinal axis of the bone
What does it mean that bone is an anisotropic material?
Meaning its mechanical properties depend on the direction of the applied forces
because of the structure and orientation of osteons,
compact bone is strongest in _____ (axial or abaxial)
Axial compression weaker in tension and weakest in shear
fractures usually propagate along tension and shear planes. Shear planes run at approximately _____º
45º from compressive and tensile stresses
Tensile loading occurs when equal and opposite loads are
applied to distract the_________ (ends or midlle) of a bone
ends
mention the type of loading
tension
mention the type of loading
compression
mention the type of loading
bending
mention the type of loading
bending/compression
mention the type of loading
torsion
mention the type of loading
shear
Maximum tensile stress occurs on a plane _______________________(perpendicular/parallel) to the direction of applied load
perpendicular
Long bones are not well adapted to resist _____________ (uniaxial/biaxial) tensile loads which are not common during normal physiological activities
uniaxial
Define compression load
Compressive loading occurs when equal and opposite
loads are applied to push the ends of the bone closer
together.
Axial compression causes the bone to
shorten and widen
Define torsion load
Torsional loading occurs when opposite moments (rotational
forces) are applied to the ends of a bone, such that
the bone twists around the longitudinal axis
Torsional loading induces shear stresses in planes:
a) parallel
b) perpendicular
c) parallel and perpendicular
c) parallel and perpendicular
fracture becomes complete when a longitudinal
fissure occurs, connecting the
proximal and distal ends of the spiral crack.
The fracture originates where
shear stress is greatest on the periphery of the bone and
then propagates due to tensile stresses distracting bone
fragments along a spiral configuration until the fracture
ends are approximately parallel or above one another
Tensile loads cause the bone to elongate and narrow. Failure occurs due to tensile forces perpendicular to a transverse
plane. Tension from the suspensory ligament and distal sesamoidean ligaments influenced the transverse configuration of the
mid-body
proximal sesamoid bone fracture shown.
Compressive loads cause the bone to shorten and widen. Failure occurs along the plane of maximum shear stress,
oriented approximately 45° from the axis of compressive loading. An incomplete dorsal cortical stress fracture of the third metacarpal
bone illustrates a fracture due predominantly to compressive loading and shear failure. Source (inset): Based on O’Brien et al. [
Define bending load
When a bending load is applied, compressive stress is
induced on the concave side and tensile stress is induced
on the convex side of the deforming bone.
Bending creates a longitudinally oriented plane, called
the neutral axis, where neither compressive nor tensile stresses are
present
The greater the distance from the neutral axis, the ____________ the tensile or compressive stress
larger
Bending creates tensile and compressive loads on different sides of the bone. Failure occurs first on the side under tension resulting in a transverse distraction fracture. The fracture then propagates on the side under compression in an oblique configuration, with or without a butterfly fragment, illustrated by a Salter–Harris type II fracture of the proximal tibial physis in a 10-day-old foal and a mid-diaphyseal butterfly fracture of the third metatarsal bone in a foal.
Implants (such as intramedullary nails) that are positioned at the
neutral axis are exposed to lower or higher levels of bending?
lower
Failure is initiated on the tensile side which is convex or concave
convex side of the bone because bone material is weaker in tension
Tensile failure causes ______________ crack propagation
until compressive stresses on the concave side of the
bone induce failure in shear at 45° to the longitudinal axis
of the bone.
transverse
Failure along the plane of highest shear stress
drives the fracture line in oblique directions, producing an _________ fracture face or ________________ fragment
oblique or butterfly
Define shear force
A shear force is one that is applied parallel to a surface or
section through a bone, causing a tendency for surfaces or
sections to slide past one another
Shear forces predispose to which type of fractures?
A shear force is an external force acting on an object or surface parallel to the slope or plane in which the surface lies.
Cyclic shear loading of an interface between regions of different subchondral bone densities in the distal condyles of the third
metacarpal bone predisposes to condylar fracture in Thoroughbred racehorse
Mid-body fractures of the proximal sesamoid bones provide a good example of which type of fractures
complete, mid-body fracture of the proximal sesamoid bone that typically has transverse orientation attributed to longitudinally directed tensile forces
Short oblique and butterfly fractures generaly result from _______ forces
bending forces which cause tensile loading on the convex side and compressive loading on the concave side of the bone
The radius is particularly susceptible to side impact loads like kick injuries typically resulting in _____________ fractures in adult horses
comminuted fractures
Simple fractures are less common and when they occur the configuration is usually either ______________ or ____________
short oblique or butterfly
In simple fractures when they occur in butterfly the fragment is on the same side or opposite side of the impact?
same side
Long oblique and spiral fracture configurations occur in the diaphyses of 3 bones, mae them
femur, tibia, humerus
Traumatic diaphyseal fractures of the proximal long bones in adult horses are often _______________ fractures
comminuted fractures due to substantial energy release at the time of the fracture
In FOALS the diaphyseal fractures of the femur, tibia and humerus occur in
spiral or long oblique configurations due to combination of compressive and torsional forces placed on the limb during axial loading
Which type of loading is responsible for the formatioon of third MC and MT condylar fractures?
Cyclic shear loading
During high-speed locomotion the load is concentrated on the dorsal or palmar aspect of the distal condyles of MCIII?
Palmar and adaptive modelling leads to increased
density of the subchondral bone
Fractures that involve significant compressive
forces can occur rarely in horses. Where is common?
in the cervical vertebrae as a result of
trauma, such as falls or impact into a fixed object
Other type in the limb can result from compression, which one?
Dorsal cortical stress fractures of the third metacarpal bone
can also be related to compression
The dorsal cortex MCIII have short oblique configuration typically propagating in which direction?
Palmaroproximal to dorsodistal direction
Define stress
Forces expressed relative to the areas of application are
termed stresses
Define deformations
deformations caused by these stresses and expressed as a proportion of the original dimensions are called strains.
Monotonic fracture occur as result as single extreme load deforms the bone or smaller repeated loads?
Monotonic is a result of single extreme load deforms the bone beyond its ultimate limit resulting i sudden complete failure
Adaptive modelling refers to changes in bone shape and internal structure in response to mechanical forces placed on the bone according to _______ law
Wolff’s
Give an example of adpatation to load in Thoroughbred racehorses
The new bone formation in response to repeated loading where there is the increase in cortical thickness and bone volume fraction
What does consiste the bone remodelling observed in replace damaged or fatigued bone
Remodelling involves resorption of bone by osteoclasts and replacement by osteoblasts in highly orchestrated and controlled series of events
define modelling
Living bone not only has the ability to change
its shape and volume to reflect the mechanical loads it
must support (modelling)
What is the role of microcrack
iniatinting the remodelling process
Fractures distal to the carpus and tarsus have beeter or worse prognosis?
better prognosis but there are challanges in poor soft tissue coverage
What are the predictable sites of stress fracture in humerus
Caudoproximal
Crainodistal
Medial diaphyseal
Caudodistal
What are the predictable sites of stress fracture in scapula?
Distal aspect of the spine
What are the predictable sites of stress fracture in carpus
dorsomedial third carpal bone
radial carpal bone
intermediate carpal bone
What are the predictable sites of stress fracture in Third metacarpal
Mid-diaphyseal and supracondylar
Parasagittal groove
Proximal palmar
Dorsal cortex
Distal condyle
What are the predictable sites of stress fracture in Proximal sesamoid
Palmar flexor region
Medial sesamoid abaxial
mid-body subchondral
What are the predictable sites of stress fracture in proximal phalanx
sagittal groove
What are the predictable sites of stress fracture in pelvis
ilial wing
pubis
What are the predictable sites of stress fracture in tibia
Distomedial
Caudoproximal
Caudal diaphyseal
Proximolateral under the head of the fibula
What are the predictable sites of stress fracture in tarsus
Dorsolateral third tarsal bone
What are the predictable sites of stress fracture in lumbar spine
L5-L6 vertebral junction
What is the most common physeal fracture in horses?
Salter Harris type II
Where is the typical sites of Salter Harris type II?
Third MC and MT distal physes
Distal femoral physis
Proximal tibial physis
Mention the different Location
Epiphysis
Physis
Metaphysis
Mention the different Direction
Diaphysis
Proximodorsal to distopalmar
Mention the different Plane for example transverse, oblique, longitudinal, sagittal and dorsal
Orientation of the predominant fracture line
Mention the different Extent
Complete
Incomplete
Mention the different Configuration
Transverse
Longitudinal
Oblique
Spiral
Butterfly
Mention the different displacement
Nonsdisplaced
Displaced
Mention the different complexity
Simple
Intermediate
Complex
Mention the different joint involvement
Non-articular
Articular
Mention the different contamination
closed
open
Mention the different other
avulsion
slab
condylar
Salter Harris type IV tend to be unstable and many require….
internal fixation
Should you perform bridging of the physis during internal fixation of physeal fractures?
NO, you should avoid if possible as they may result in premature closure and development of angular limb deformity
Type V injuries are rare are they detected radiographically?
No they are not radiographically detectable in the begining as they manifest as a progressive angular limb deformity
an axial proximal sesamoid fracture occurring concurrently with a displaced lateral condylar fracture is associated with a _________ prognosis
poor
Can rupture of a vessel such as popliteal artery in femoral fracture
or thrombosis of palmar/plantar digital arteries in acute fetlock breakdown injuries can be the cause of euthanasia?
yes
What are the most common reasons for complete fracture?
Neoplasia and osteomyelitis, pituitary pars intermedia dysfunction (PPID)
