AO_chapters Flashcards
preop management of fx patient
ABCDairway, breathing, circulatory, other disabilitiesSPO2, auscult, IV access/fluids, imaging, full ortho neuro PE
benefits to pain mgmt for fx patient
decrease anxiety/stress and it’s associated hormonal and metabolic derrangementsprovide patient comfort
most effective analgesic time period
PRIOR to onset of pain (surgery)
advantages of multimodal pain therapy
selectivity to target multiple sites of pain pathadditivite/synergismreduced dosingreduced toxicity
define neuroleptanalgesia
combo of neuroleptic drug (ace) and analgesia (opioid)
infection rate of CLEAN ortho procedures
2.5-4.8%
most common isolate causing ortho infxn
Staph intermedius
host risk factors for sx infection
age (>8yrs) obesitydistant infection, endocrinopathyinadequate skin prepprolonged axpropofol
intraop risk factors for sx infection
sx > 90 mexcessive electrocauterybreak in asepsisbraided/multifilament sutureimplants
use of periop prophy Ab decreases rate of infxn_______
use of periop prophy Ab decreases rate of infxn 4 fold in clean procedures.
traditional recommendation for prophy Ab in clean procedure
in clean procedures generally NOT indicated UNLESS>90m surgerymetal implants usedextensive ST damagecefazolin–bactericidal given IV 30 min prior to sx
AO fracture classification
1 humerus2 RU3 femur4 tib/fib1=prox2=shaft3=distalA= single fxB= wedge/butterflyC=complex
open fracture classification
I. bone penetration thru skin (small puncture hole/laceration < 1 cm); CLEANII. > 1cm laceration with fracture communicating with skin; mild ST traumaIII. A severe comminution; hi energy, ST flaps but available for wound coverageIII. B severe comminution; hi E; bone exposure; periosteum strippedIII. C severe comminution; hi E; bone exposed with damage to arterial blood supply
physeal fracture classification
Salter HarrisI growth plate II growth plate metaphysealIII growth plate epiphyseal (intraarticular)IV metaphyseal/epiphyseal (intraarticular)V compressionVI asymmetric compression
objectives for fracture repair
reduction/alignmentrigid stabilization/immobilizationmaintain blood supplyearly return to normal function
mechanical and biological factors for fractures
mx: fx configuration, reconstruction or not, concurrent ortho injurybx: age, fracture location, ST injury
pros/cons to open vs closed reduction of fx
open: visualization, bone grafting, anatomical recon BUT incr sx time and ST injury/blood supplyclosed: preserve ST/blood supply, decr contamination BUT at the expense of fracture alignment/recon
Three ways of fracture planning
direct overlaybone specimenintact contralateral bone
major benefit of fully reconstructed boney column
shares the wt bearing load of the limb during fx healing
review of post op radiograph criteria
4 AsA=appositionA=alignment (50% is necessary to prevent delayed union)A=apparatusA=activity
rehabilitation goals
prevents musculoskeletal disabilitydecreases healing timefacilitates restoration of normal function
rehab includes
cryotherapy–ICE in acute < 72 hr period; vasoconstrict, min fluid/edema, decr nerve conduction, encourage muscle relax; w compression decr temp by 27 deg Cheat therapy– > 72 hr period, vasodil (NOT in nerve patient); incr metabolismmassage–incr local circulation, decr muscle spasm, attentuate edema, brkdown scar tissuetherapeutic exercise–pROM; maintain normal joint motion, sensory awareness, blood flow improvement; build strength, agility/coordinationtherapeutic US–treats chronic scare and adhesions NM stimulation–creates artificial contraction
types of massage
EFFLEURAGE–superficial/light strokingPETRISSAGE–kneadingTAPOTEMENT–percussion/tapping
biological fracture healing goals
flexible fixationeliminate anatomic reconstructioncreate axial alignmentless surgical traumaindirect bone healing w calluspreserve blood supply
role of screw
interfrag compressionfixing of a splinting device (plate, nail, fixator)
difference btwn cancellous and cortical screws
cancellous screws1. larger outer diameter (thinner inner core)2. deeper thread3. larger pitchused in metaphyseal and epiphyseal bone
cortical screw
used in diaphysisas size increases strength increasesscrew diameter should not exceed 40% of bone diameter
3.5 mm cortical screw characteristics
2.4 core diameter (use 2.5 drill bit)3.5 thread diameter6 mm head hexagonal recess
T/F self tapping screws can be used as lag screws
FALSE; avoid self tapping screws to be used in lag fashion bc may cut a new hole/threads
what is a shaft screw
cortical screw with short threads and a shaft that has a diameter equal to that of a threadused as a lag screw in diaphyseal bone
what is a cannulated screw
central hollow cored and are inserted over K wires that act as a guide.3.5 mm cortical6.5 mm cancellous
application of a lag screw
can use fully or partially threaded NONself tapping screwsfully threaded: overdrill CIS cortex (gliding hole= thread diameter)partially threaded: threaded portion only engages TRANS cortex
Lag screw insertion guidelines
EQUIDISTANT from fracture edges (middle of the fragment)PERPENDICULAR to the fracture planeconsider countersink (remeasure) and washer to evenly distribute forces
what happens if the lag screw is NOT perpendicular to the fracture plane
shear forces displace fracture fragments
rule of thumb for tightening plate/screw based on screw sizes
2.0 mm two fingers2.7 mm three fingers3.5 mm whole hand
screw placement into plate to ensure axial alignment of the plate to the bone
- screws are first applied at each end of the platethen close to the fracturefinally remaining holes are filled2. ALT if straight alignment, fill closest to fracture firstthen alternate filling towards the end of the plate
functions of a dynamic compression plate
compression (eccentric), neutral (middle), bridging, or buttress
hole design of DCP allows compression and how much displacement of the fracture fragments
1.0 mm per DCP hole using 3.5/4.5 mm 0.8 mm per DCP hole using 2.7 mmcan place one or two compression screws on either side of the fracture (have to loosen first screw on same side to move fragment and then retighten)
oval shape of DCP holes allows what degree of screw angulation
25 degrees longitudinally7 degrees transversally
gold eccentric drill guide is how far off center
1.0 mm (therefore allows for compression)
available metal for LCDCP vs DCP
DCP stainless steelLCDCP stainless steel and titanium (outstanding tissue tolerance)
limited contact dynamic compression plate (LC DCP) advantages
- scalloped underneath-allows for the area of the plate/bone contact or footprint to be greatly reduced)-spared capillary network under the periosteum-even distribution of stiffness (limits stress risers at screw holes)-makes contouring easier-does not “kink” plate holes2. symmetrical plate holes-allows eccentric screws in either direction-plate holes are evenly distributed
symmetrical shape of LCDCP holes allows what degree of screw angulation
40 degrees longitudinally7 degrees transversally
what drill guide is used in LCDCP
universal spring loadedcompressed–>neutral positionnot compressed–>eccentric placement for compression
Veterinary cuttable plates use
versatile and used in small animal patientscan be cut to lengthcan be stacked to incr stiffness; but relatively weak plate1.5/2.0 mm2.0/2.7 mmNOT A COMPRESSION PLATE; circular round holes
reconstruction plate use
deep notches inbtwn holescontouring can occur in an additional planeoval holes allow for compression
types of special veterinary plates
acetabular plates; T/L plates; Double hook plates (prox femur); TPO plates; tubular plates
compression vs neutralization plate functions
compression: reducible fractures (simple transverse); axial compressionneutralization: plate protects interfragmentary compression; neutralizes bending forces
prebending plate functions to…
…prebending plate 2 mm at fx line functions to compress opposite cortex
Buttress vs bridging plate functions
buttress: prevents collapse of fx (ex. metaphyseal fx); plate is subject to full loadingbridging: nonreducible comm fx; aka biological plating; long and strong plate used; subjected to full loading; maintains length/alignment and prevent axial deformity; CALLUS
implant combo particularly effective for bridging application
plate-rodsynergistic mechanical propertiesrod 40-50% medullary canal diameter–> increases fatigue life of plate, decr strain on empty screw holes
advantages of locking plate/screw systems
Stability btwn screw and plateplate does NOT need intimate contact with boneplate does NOT rely on frictionexact contouring NOT essentialreduced contact w bone maintains blood supplymay reduce bone resorption under the plate
LCP locking compression plate
COMBINATION hole plate (conventional–angle or compression or locking screw)3.5 mm or 4.5 mm systems
locking head screw (LHS)
self tappingconical threaded head and threads/locks into plate
unilock plate system
2.0 mm or 2.7 mm systemslocking plate/screw design
CRIF Clamp rod internal fixator system
excellent versatilitygood contouring capabilityease of applicationminimal instrumentationminimal contact with bone
contouring of plates rules of thumb
repeat bending should be avoided because it weakens the platebend plate btwn holes to avoid stress riserslocking plates should used bending teesbending press, hand held pliers, bending irons
pros to positive profile pins
shaft diameter is the same throughout the pin reduces bending stress; stronger; better bone purchasethread diameter is greater than shaftpredrilling a hole smaller than core diameter improves quality
T/F double clamps are as strong as single clamps
FALSE:double clamps may be used to connect one connecting bar to another NOT as strong as a single clamp
types of ESF connecting bars
Stainless steel (historically)Carbon fiber–radiolucentTitaniumAcrylic/epoxy
T/F Mechanical studies show that a 19 mm diameter acrylic/epoxy bar has similar rigidity as 3.175 mm stainless steel bar
TRUEMechanical studies show that a 19 mm diameter acrylic/epoxy bar has similar rigidity as 3.175 mm stainless steel bar
advantages of ESF application
great in areas of less soft tissue coverage, also mand/maxapplied closed +/- fluoropreserves blood supply
Rules of thumb w ESF fixation
AVOID ST/neurovascular structuresAvoid ST injury with use of half pins/unilat framediameter pins < 25% diameter bonemin 2 pins per fragment (3 optimal) placed at least 2 pin diameters from fracture edge
T/F Bilateral ESF are more stable than unilateral ESF
TRUE BUT bilateral ESF penetrate the skin twice and lead to more ST injuryBest avoided if two unilateral ESF in two different planes (biplanar configuration)
angled vs parallel pins in ESF
Angled pins offers mild incr stabilityMORE threaded parallel pins > purchase to fewer angled pins
ESF clamp placement
bolt locking the pin should be placed closest to the bone to shorten the pin length and stabilize the frame~ 1 cm away from skin
ILN interlocking nail
stainless steel into IM cavity held by bolts/screwsresist axial, bending, and rotation
standard ILN has bolts how far apart
6.0 mm ILN 22 mm apart8.0 mm ILN 11 mm apart
bolts used with ILN
VERY STRONGonly threaded into near cortexrest of shaft is unthreaded and has increased bending strength
what mode are ILN placed?
bridgingused in nonreducible comm fx; aka biological; subjected to full loading; maintains length/alignment and prevent axial deformity; CALLUS
ILN can only be passed (normo or retrograde)
ILN can only be passed NORMOgradeBUT can prepare the medullary canal with retro or normograde
ILN lock which side (prix or distal) fragment first
pass ILN normogradelock DISTAL fragment first with screw/bolt after achieving length/alignmentcorrect for rotation and additional alignment prior to locking proximal piece
how to remove ILN
first remove screws/boltsattach extension setextract nail
IM pin alone recommended diameter and counteracting forces
should be ~70% bone diameter at isthmusonly resists bendingNOT collapse NOT rotationstainless steel aka steinmann pin; adjunct repair is necessary to counteract all forces
most common point style for IM pin
Bayonet3-face trocarDiamond point
difference between steinmann pin and k-wire
both stainless steelk-wire 0.8-2.0 mmsteinmann pins 2.0-5.0 mm
most effective way of counteracting rotational and axial forces around an IM pin
addition of ESF (tie in or IM pin + ESF)
how to add bending strength to IM pins
STACK with 2-3 pins in medullary cavity to incr bending strength but does little to axial or rotational stability.
repair of distal physeal fractures and pins
CROSS PINfragments must have good contact and ideally interdigitate to resist rotation
recommended IM pin diameter when using plater rod
plate rod = buttress mode (prevents collapse)reduced bending stress<50% bone diameter
orthopedic wire material
316L stainless steelmalleable 16-24 gaugethe larger the diameter the greater the bending and tensile strengthdo not kink or have tissue inbtwn wire and bone
ideal fracture configuration for using orthopedic cerclage wire
long oblique fracture where fracture length is at least 2 x the diameter of the bone
how many cerclage wire is recommended per fracture fragment
at LEAST 2 cerclage per fracture fragmentspaced between half to one bone diameter apartshould be placed perpendicularly to fracture (can use skewer pin to hold) USED AS ADJUNCT REPAIR
forces that cerclage wire may counteract
axial compression some rotation
three methods of tying cerclage wire
TWIST —must twist and pull evenly so wires wrap along each other, NOT one over the other; alt. twist and flatten techniquesingle loopdouble loop
with twist cerclage, how many twist should remain prior to cutting the wire
cut with 2-3 twists remaining with twist and pull methodcut with 5-6 twists remaining with twist and flatten methodDO NOT bend (will decrease initial tension)
with loop cerclage how much wire remains when cutting wire off
use wire tightenerachieve max tension, bend wirerelease tension and wirebend wire armcut with 0.5-1.0 cm remaining and press flat
tension and load to failure for 1.0 mm twist, single and double loop cerclage
tension load at failuretwist 70-100 N fail at 260 Nsingle 150-200 N fail at 260 Ndouble 300-500 N fail at 666 N (2.6 x stronger)
repair of avulsion fractures
- lag screw (may predispose small fracture piece to break)2. two pins and cerclage (pin and tension band tech)
pin and tension band technique for avulsion fx repair
pins placed perpendicularly to fracture and parallel with each other (to counteract rotation)tension band counteracts tension forces and places them into compressive forces across the fracture site
where to drill the hole to pass a tension band
hole is drilled transversely approx the same distance below the fracture line as the pins are above the fracture line
three phases of bone healing
inflammatory : 3-5days; disruption of blood vessels, hematoma, lack of mechanical supportrepair: hematoma replaced with GT (angiogenesis/capillary regrowth/growth factors for bone formation), slight incr in mechanical strengthremodel: wks to months, incr strength as fibrocartilage is formed and remodeled to bone (Haversian progress)
the amount of callus produced in healing depends on what…
the amount of callus produced during healing depends on the stability of the fracture (greater instability, greater callus)
define strain
strain is defined at the deformation (or change in gap) occurring at the fracture site relative to the size of the gapthe amount of strain influences the type of tissue that forms in the fracture gap
bone formation and strain
the amount of strain influences the type of tissue that forms in the fracture gapbone forms only in stable environment with very LOW strain < 2%
source of growth factors in inflammatory phase
first source of mitogenic growth factors= platelets at the site of traumaPDGF, TGF Bother angiogenic factors : endothelial derived VEGF, acidity, PG E1 and PG E2later, macrophages stimulate fibroblasts thru FGF to initiate fibroplasia
source of blood supply in initial healing phases
EXTRAOSSEOUStransient, but comes from adjacent soft tissuesrevascularizes the hypoxic fracture site.
what does resorption of fracture ends do for inter fragmentary strain
widens the fracture gaplowers strain (but still remains hi)minimizes deformation in local tissues
repair phase characterized by what cell type and tissue
mononuclear cells (macros) and stimulation of fibroblastscapillary ingrowthGRANULATION TISSUEincr in mechanical strength, but strain remains hiCOLLAGEN more abundant (initially I, II, III) TYPE I COLLAGEN PREDOMINATES
collagen fibers in repair phase of bone healing resist how much elongation
collagen fibers resist elongation up to a max 17%
where do mesenchymal cells originate from in order to ddx to chrondrocytes or osteoblasts during repair phase
mesenchymal cells within cambium layer of periosteum, endosteum, bone marrowbeing proliferating and ddx to chondrocytes or osteoblasts during repair phase
tissue types included in the repair phase of secondary bone healing
hematoma–> GT –> connective tissue–> cartilage –> cartilage mineralization –> woven bone formation
external callus results in increased diameter of the fracture—which leads to what
strength incr by power 3rigidity incr by power 4decreases interfrag strain
ultimate tensile strength of compact bone
130 Nm/mm^2ability to elongate is < 2%
T/F at the end of repair phase, the injured bone has regained enough strength and rigidity to allow low impact exercise
true
remodeling phase in bone healing
is a balance btwn osteoclastic resorption and osteoblastic deposition governed by Wolff’s law and modulated by piezoelectricity
define pizoelectricity
a phenomenon in which electrical polarity is created by pressure exerted in a crystalline environmentwith axial loading, electropositive convex (osteoclastic); electroneg concave (osteoblastic)
what do medullary implants do to bone blood flow
IM pins and/or reaming of medullary cavity temporarily disturb blood flowcauses reversed centripetal flow for intense bone remodeling at bone fx site
unreamed vs reamed ILN affect on blood flow
unreamed attenuates blood flow 30%reamed attenuates blood flow 70%
biological fixation of comminuted fractures is associated with…
incr callusaccelerated radiographic unionearlier gain in strengthearly return to normal function
Primary or direct bone healing
stable fracture fixationwithout callus formationdirect osteonal proliferationinclude both gap and contact healing
how do gap and contact healing of direct/primary bone healing differ from indirect/secondary bone healing
Both gap and contact healing (direct/primary healing) differ from indirect/secondary bone healing by the ABSENCE of resorption of the fracture ends
contact healing of primary bone healing occurs when?
< 0.01 mm defectinterfragmentary strain < 2 %=primary osteonal reconstruction, w lamellar bone oriented normally initiated by cutting cones
define cutting cone
cutting cones occur in contact primary bone healingclosest to fracture linesosteoclasts line the spearheadosteoblast follow in the rear so that boney union and Haversian remodeling occur simultaneously
daily progress of of cutting cones across a fracture site
50-100 micrometers/day
difference btwn contact and gap healing of primary bone healing differ
contact < 0.01 mm defect; boney union and remodeling occur simultaneously;lamellar bone in normal orientationgap: 0.008-1 mm defect; boney union and remodeling occur in two separate steps; lamellar bone perpendicularBOTH FORM BONE WITHOUT CALLUS
define gap healing
0.008-1 mm defectinterfragmentary strain < 2 %boney union and remodeling occur in two separate stepslamellar bone oriented perpendicularly (weaker) w secondary osteonal reconstruction (3-8 weeks)
goals of biological fracture fixation
restore length, alignmentlimit manipulation and disruption of ST, hematoma
perferred techniques for stabilization with biological fracture fixation
ESFILNMIPO
considerations for what adjunct therapy to promote biologic osteosynthesis
fresh autogenous graftautogenous cancellous is most effective material to promote healing (osteogenic, osteoinductive–controversial, osteoconductive)
properties of bone grafts
osteogenic–graft that supplies/supports bone forming cellsosteoinductive–induces bone formation in a site where no bone will occur normally (recruits to the area); demineralized bone matrixosteoconductive–scaffoldosteopromotion–enhancement of regenerating bone; PRP
Properties of demineralized bone matrix
most commonosteoinductive, osteoconductivechemical sterilization
rank the areas for greatest autogenous cancellous bone collection
ilium > prox humerus > medial proximal tibia
how soon after should one wait to take a second cancellous autograft from the same location
12 weeks for femoral or humeral site
cell viability for fresh cancellous autograft
85-100% decreases to 57% if in blood soaked sponge 3 hrobtain immediately after fracture reduction/stabilization in order to use fresh
only osteoconductive implants with biomechanics properties
Frozen segments of allogenic bone(autogenous cancellous graft has scaffold properties but does NOT have mechanical support)
main complication with allogenic bone segment
incomplete resorption–>fatigue failureinfection
osteoconductive calcium sulfate
medical gradevoid filler in non weight bearing applicationscompletely resorbed 2-5 weeks in animals+/- impregnated with Abaffordable
Bioceramic osteoconductive examples
Hydroxyapatite (HA)Tricalcium phosphate (TCP)HA slower to resorb that TCPporosity for bone ingrowthradioopaque (can interfere with rads)
periosteal stripping in immature animals
results in production of a callus AWAY from the bone as osteoprogenitor cells get pulled with the periosteum
three factors that affect the size of bone callus
- interfragmentary strain2. local blood supply3. hypoxia (encourages chondrocytes>osteoblasts)
radiographic signs of indirect bone healing
5-7 days post op–widening of fracture edges10-12 days post op–mineralization of callus (boney callus)30 days post op–disappearance of fracture line90 days post op–complete remodeling
4 A’s of radiographic assessment of bone healing
alignmentappositionapparatus/implantsactivity/healing
T OR FClinical union is faster in sites with abundant cancellous bone and highly vascularized marrow (metaphysis)
TRUE
indications for plate removal
- osteomyelitis2. pain on palpation of bone3. radiographic evidence osteopenia
T OR FFractures undergoing direct primary healing are initially stronger than those undergoing indirect bone healing with callus
FALSEFractures undergoing direct primary healing are initially WEAKER than those undergoing indirect bone healing with callus pg 92
define a delayed union
fracture that takes longer to heal than anticipatedquantitative judgement–no specific timeline, need serial radiographsshould be suspected when limb is more painful and use is less than anticipated
Causes of delayed union
factors that negatively influence fracture healing1. biological–vascularity/infarction–initial contamination (ie. open wounds)–concurrent systemic disease/trauma2. Mechanical–stability (creates motion and incr intrafragmentary strain that exceeds tissue tolerance)–MOST IMPORTANT FACTOR–initial trauma–initial transportation of patient
what is the fate of a piece of bone that has been deprived of its vascular supply
sequestrum (dead/dying bone–radiolucent)surrounded by an involucrum (new bone–radioopaque)cloaca
Implant related factors leading to instability of fracture and subsequent delayed union
small implant sizeinsufficient bone purchase/contactthreaded (better than) smooth pins
T/Fstability = rigidity
FALSE Stability should NOT be confused with rigidityex. circular ESF
treatment of delayed union
continuing or augmenting the technique originally usedrather than changing it completely (unless external coapt–change to internal fixation)continued monitoring for bone healing+/- bone graft augmentation +/- bigger implant/stable implant if needed
define nonunion
fracture that has failed to heal and does NOT show signs of any further healing/progressionusually several months
classifications of nonunions
- viable/biologically active–variable amounts of callus but failed bridging2. nonviable/biologically inactive–no callus
Causes of nonunion
- poor decision making and technical failure; inadequate fracture fixation–>instability, hi strain2. big fracture gap3. vascularity (toy breed dogs distal radius)
what can happen (rare) to a biologically active nonunion that has variable amounts of callus (unmineralized fibrocartilage)
can become lined with synovium= pseudoarthrosis
how are biologically viable nonunions further classified
- hypertrophic–enlarged bone ends, elephant foot2. slightly hypertrophic–horse hoof3. oligotrophic–no radiographic signs of callus BUT capable of growth; rounded edges and undergo decalcification(depending on how much callus is present)
how are biologically INactive or nonviable nonunions further classified
- dystrophic–poorly vascular, callus at one end but NOT the other2. necrotic–major fragments devascularized, no callus3. defect–large bone defect4. atrophic–most extreme, defect with resorption at fracture ends
another alternative way to classify nonunions
Callus: hypertrophic, slightly hypertrophicno callus: viable oligotrophic, all other nonunions
radiographic signs of nonunion
persistent gapvariable amount of callus (non-bridging)rounded, sclerotic fracture endsobliteration of medullary cavitySequestraadjacent osteopeniainstability–implant loosening/bone lysis
diagnostic modality to help ddx btwn nonviable vs viable nonunions
bone scintigraphy
treatment for nonunion fractures
Sx intervention!remove loose implants, sequestra debride nonviable tissue (may need osteotomy–shortens leg)stabilize fracturegraft+/- culture and Ab 6-8 weeks
common finding with femoral nonunions
associated with rotational instability and patellar luxation
define malunion
healed fractures in which anatomical bone alignment was not achieved or maintained during healingusually ALD present with variable functional outcome(minor < 10% or 10 degrees, major > 10% or 10 degrees
common site of malunion
pelvic fracturesmay lead to reduction in pelvic canal (obstipation, dystocia)
usual cause of malunions
improper treatment (inadequate reduction or loss of reduction) of the original fracture in which anatomical bone alignment was not achieved.
in immature animals, what further complicates malunions
growth plate fractures or damage leading to ALD
name 7 angular deformities
- frontal plane: varus (towards medial sagittal plane), valgus (away from median sagittal plane)2. Sagittal plane: procurvatum and recurvatum3. of the axial plane: internal and external rotation4. shorteningsimple = one affected planecomplex = more than 1 affected plane
treatment of malunions
corrective osteotomies if they cause a functional problem
how do small animal patients compensate for minor ALD with minor limb shortening
compensate for minor shortenings by extending the joints a little more than usual
distraction osteogenesis
for young dogs with ALD with limb shorteninguse circular ESF and create osteotomydistraction goal: 1 mm per day (at a rate of 3-4 times a day)
define osteomyelitis
inflammatory condition of bone most commonly caused by infectious agentshematogenous or traumatic insultacute or chronic(chronic post traumatic most common)
causative bacterial agent for osteomyelitis
60% staph speciesstaph intermediusgm positive fibronectin receptors used for adhesion
T/Fopen fractures have an increased incidence of infection as bacteria have a direct opportunity to enter tissues
TRUE
if normal bone is resistant to bacterial colonization and infection, when does osteomyelitis occur
when the vascular supply is compromised and tissue ischemia is present with bacterial contamination
local factors involved in formation of osteomyelitis
tissue ischemia/impaired blood supplybacterial contaminationbone necrosis/sequestrafracture instabilityforeign material or implants
three components to any biofilm
offending microbemicrobe-produced glycocalyxhost biomaterial surface
how do biofilms help protect bacteria
biofilms protect bacteria from the action of Ab, impede cellular phagocytosis, inhibit Ab ingress, and alter B- and T-cell responses
3 mechanisms of Ab resistance of bacteria with biofilm formation
- biofilm is a molecular filter2. near quiescent (dormant) growth pattern of biofilm microbes render Ab ineffective3. harsh environment (low pH, incr Co2,, decr O2, and hydration) inactivate Ab
clinical signs associated with acute osteomyelitis
febrile, localized swelling and pain, systemically ill
clinical signs associated with chronic osteomyelitis
localized signs, draining tracts, lameness
how to confirm osteomyelitis
positive microbial testing in fracture region, sequestra, local necrotic tissue, or implantsdraining tract cultures may or may not be involved with infectious process
treatment of acute osteomyelitis
draindebridesystemic Ab ( IV for first 3-5 days then oral 4-8 weeks)rigid stabilizationdirect bone culture delayed wound closure
treatment of chronic osteomyelitis
meticulous debridement– need to remove biofilmestablish drainagerigid stabilization (remove old /loose implants first if needed)+/- bone graft6-8 weeks Ab
T/Fbone will heal in the face of infection if stable
TRUE
most common Ab carrier implant
PMMApolymethylmethacrylate
Which one has not been reported as a risk factor for increased risk of infection TPLOs.a) increased BWb) skin staplesc) genderd) use of braided suture material e) Simultaneous bilateral procedures
d) use of braided suture material
Frey et all JAVMA 2010 902 CCL Sx risks of infection/inflammation w skin staples
1.9x greater with staples (p=0.04).Recommendation minimum distance staples-to bone 4mm for safe application of staples.
Gallagher 2012 vet surgeryinfection after TPLO and implant removal showed what Ab sensitivity for empirical Ab recommendations
94% S gentamicin (may argue local Ab beads)67% S clavamox31% S enrofloxacin
benefits of local Ab administration for treatment of osteomyelitis
less systemic side effectshigh local dose (serum concentration 10-20x)prolonged dose (use of Ca sulfate beads are biodegradable over 6-8 weeks; PMMA most commonly used)USE CIDAL, water soluble AB
major cause of implant failure
TECHNICAL FAILURE (improper implant size/selection/application)not infection
methods of bone implant composite failure
can fail at level of implantcan fail at level of bone (bone healing)can fail at level of attachment of implant to bone
mechanically, why does an implant bone composite fail
cyclic loading and fatigue(initial loads are not as important as cyclic loading)
revisions of implant failure
improve mechanical and biologic environmentmay need to change all implants or augment old onesaugmentation of old implant is only considered IF alignment and reduction are maintained and failed implant will not hinder subsequent healingconsider GRAFTS
most commonly proposed mechanical factors leading to refractor after implant removal
limb loaded too quicklystress protection under the area of plate, open bicortical screw holes (stress risers)***most importantremoval of implant prior to clinical union
stress protection from bone plate application
rigid plate fixation has been associated with stress protection and subsequent bone lossincreased bone porosity decreased bone mineral density
screw holes act as stress risers have their greatest effect in what force
screw holes have their greatest effect in torsion
implant material of choice
METAL (SS or titanium)high strength and stiffnessgood ductilitybiologically well tolerated
define stiffness
depends on the material, design and dimension of implantaka modulus of elasticityslope of a load vs deformation curveosteosynthesis restores bone stiffness temporarily while fracture healing restore bone stiffness permanently
stiffness or modulus of elasticity of titanium vs stainless steel
stiffness of titanium (110 GPa) is half that of stainless steel (200 GPa)in other words, titanium plate would deform nearly twice as much as a steel plate
T/FLess stiff implants abolish stress shielding
FALSEless stiff implants REDUCE but do not abolish stress shielding
define strength
ultimate stress limit that material/structure can withstand without deformation/rupturestrength determines the level of load up to which the implant remains intact
compare strength of commercially pure Ti, to stainless steel
ultimate tensile strengthCP Ti 860 MPa (10% less than SS)SS 960 MPa
T/F In internal fixation, the resistance to repeated load, which by result in fatigue failure is more important than strength
TRUE
define ductility
implant material characteristic that characterizes the degree of plastic deformation it tolerates before rupturehelps determine the ease of contouring
titanium vs ss ductility
titaniums offer less ductility than stainless steel
define corrosion resistance
determines how much metal is released into the surrounding tissue
stainless steel vs Ti corrosion resistance
SS is highly corrosive resistant though “fretting” local corrosion can occur (screw head moving in relation to plate hole)CP ti shows nearly NO corrosion making it a better biologic material
allergic reactions to metal
nickel containing SS 1-2 %no reaction with titaniumVery little data
disadvantage of biodegradable implants
they have limited mechanical properties and therefor should only be used in areas of minor loading
methods for filling bone defects
- autocortico, cancellous, or corticocancellous grafts2. allograft3. Distraction osteogenesis4. deproteinized bone (kiel bone)5. synthetic bone fillers (HA, tricalcium phosphate)
T/FVery high levels of strain can be present within small fracture gaps
TRUEVery high levels of strain can be present within small fracture gaps even under conditions where the displacement may not be perceptible
