Midterm Flashcards
Bone strength factors
Material, structural, rate of load, orientation of load
Rate of load applied=
Viscoelastic properties
Direction of load=
anisotropic (identical properties in all directions?)
Heirarchy of strength in response to forces
Compression > tension > shear
Name Fx mechanisms
Tension, compression, torsion, shear, bending
Compression: aka, type of Fx, where
Axial load; short oblique; vertebral bodies.
Tension causes what type of Fx and where
Avulsion at apophyses (traction physes- lig/tend attchmt)
Shear- type of Fx
SH4
Bending- type of Fx
transverse or short oblique starting on tension surface (+/- Y with butterfly segment)
Torsion- Fx type
Spiral
Configuration of Fx classification
Incomplete (greenstick vs fissure), complete (transverse, oblique, spiral, comminuted, segmental)
Greenstick Fx- describe, produced by, Fx types
by bending/torsion, still weight bearing- both cortices involved- oblique/spiral
Transverse Fx- force type
Bending
Transverse- reduction withstands what forces
axial/compression
Oblique vs spiral
Oblique: cortices on same plane
Oblique- causes
compression and bending together
Comminution- define
three segments with connected Fx lines, multiple forces, higher energy trauma
Segmental- define
Three pieces but no interconnection- intact cylinder between fxs, +/- avascular segment from disrupted medullary vascular supply
Open Fx classifications
I- clean, laceration 1cm
III- extensive damage, worse prognosis, wont ever be perfect
Type of bone in diaphysis, healing speed
Mainly cortical, haversian system (mostly mineral, some osteoblasts) slow turnover/healing
Type of bone in metaphysis, healing speed
cancellous with mantle of cortex, muscle attachments, less mechanical forces applied, good blood supply, fast turnover
Long term effect of SH fx
physeal fracture- impeded growth, poor long term fxn
When joint involved in a fracture, treatment MUST have
Anatomic reduction and rigid fixation!
SH scheme
SALTR - straight (physis), above (thru meta/phys), lower (thr phys/epi, through (epi/meta/phys), compressive cRush
Effect of all SH fx on all dogs and cats
growth plate closes
Where do SH fx occur? (Boards)
Zone of hypertrophy (where cells get large before mineralizing)`
Describe Fx
open/closed, configuration, location, R/L, bone, displacement
Describe displacement of fx
Distal to prox
Fracture assessment score
Fx, owner, patient- high (10) good- less plates, fast heal; low (1) slow heal, need plates
Primary goal of fracture management
Early and complete return to fxn (small incisions, anatomic reduction, rigid fixation, direct bone healing, good rads)
Outcomes of anatomic reduction
Load sharing, weight bearing, fracture healing, alignment
Biologic fixation- describe
The gardener approach, preserve environment, use bridging osteosynthesis- align ends of bones in functional position, let nature heal
What has greatest impact on limb function
alignment >reduction
Define fixation
implant physically engaging bone
Define stabilization
dont touch bone- cast/splint
What does union depend on in bone healing
Mechanical and biologic env- haversian systems laid down along lines of stress
Secondary healing- define
Body’s natural healing, inflammatory–> reparative –> remodeling
Define reparative phase
extra/periosseous blod supplu revascularizes, bringing fibrous tissue for support (–>fibrocart –> cart –>woven)
Describe remodeling phase
Woven to lamellar bone
Primary healing- define, requirements
Sx intervention with plates/screws (not ExFix), anatomic reduction and rigid stabilization (minimal callus formation)
Two forms of primary healing
Contact (direct apposition. MNGC osteoclast chewing, osteoblast laying haversian) or gap healing (
Difference between primary healing types
Contact- endochondral ossification; Gap- woven bone (no fibrous/cartilage- just bone)
Faster healing: meta or diaph? why?
Meta- less bending, more blood, cancellous
When will callus be evident on rads
2-4 weeks (young faster than old)
Segment vs fragment
seg- big pieces at end; frag- little pieces in middle
Primary site of bone graft- dog/cat
Greater tubercle of humerus (also use iliac crest, prox tibia) (diaphysis is yella marrra)
Indications for graft
Enhance unions, replace bone loss, stimulate fusion in arthrodesis
Dog/cat histo graft type
Cancellous (vs cortical, corticocancellous)
Osteogenesis- def, histo type
Direct placement of osteoblasts (and osteoprogenitors) from cancellous
Osteoinduction- def, histo type
Causing mesenchymal cells to differentiate into osteoblasts via cytokines like BMP (corticocancellous)
Osteoconduction- def
Trabeculae of bone transfered to act as scaffold for capillaries and incoming osteoblasts, evenutally resorbed
Structural support- graft type, describe
Cortical only- usually allograft; never complete remodel- creeping substitution
Define “coapt”
To approximate
Toggling- define, goal
leverage pieces against each other, 50-100% apposition and functional alignment
What forces does coaption reduce best
Bending
Copation indications
Temp immob, young fx, distal fx, simple/stable fx, lig/tend inj
Effect of coaption post surgery
No increased stability, higher risk of fracture disease
Cardinal rule of coaption
Immob prox and distal joints
Schanz bandage
Soft, padded, like MRJB
What position must p be in for lateral coaption splints
Functional standing- not extension
Spica- describe
Splint or cast (hard material), goes proximally over midline then wrapped around body
Spica indications
Proximal to elbow
RJB- indications, rule of thumb
distal to humeral and femoral condyles; 1 lb cotton/20lb dog
RJB- fxn
Decrease swelling, prevent closed going to opened
Mason-meta- describe
Spoon splint
Mason meta- indications
distal to carpus or tarsus/hock
Mason-meta- dont use on what?
Radius/ulna fx- cant immobilize prox joint
Velpeau sling- describe
hold forelimb against body, non=weight bearing
Velpeau sling- indication
Shoulder injuries
Figure of 8- bandage with similar effects
Ehmer sling
Figure of 8 and Ehmer function, differences
Non-weight bearing, Prevent abduction, flex hip, internally rotate- Ehmer comes around waist
What do Ehmer bandages prevent
Quadriceps tie down- stifle lock from quad fibrosis due to hyperextension- young cats/dogs
ExFix best for- Fx type
Comminuted, open, infected, non-union, arthodeses
What function does ExFix provide to fx
Stable, but NOT rigid fixation
ExFix- forces counteracted
Compression, bending, rotational
ExFix- advantages
Open or closed application, stable, post-op adjustments, early weight bearing mitigating fracture dz, economical
Types of Ex Fix
I- half pin splintage, uniplanar, unilateral; II- full pin splintage- uniplanar, bilateral (through two skin); III- biplanar, bilateral half and full splintage
Which type of exfix cant be used above elbow/stifle
Type II (and type iii)
Most used ExFix types in gen prac
Linear
What is the weakest link in the exFix
Bone-pin interface
Maleffects of smooth pins- exfix
loose so caused periosteal rxn and resorption, had to angle for surface area
Threaded pins in exfix, describe
Positive profile- threaded above core diameter, harder to extract- faster healing
Type of drill, ExFix
low speed, high torque
Pin stiffness in ExFix
Inversely proportional to distance between cis and clamp^3
Pins per segment
3-4 per major segment
Fixation pin diameter rules
no more than 30% diameter of bone
KE vs SK
KE- no threaded pins, one diameter, cant add/subtract clamps, not radiolucent, rod weaker; SK- PPP, allows pre-drilling, bigger/stronger connecting rod, more stability
Bone healing in SK system
Secondary! NOT rigid - only plates and screws give primary
Most common form of intFix in gen prac, goal
IM fixation- three point fixation
IM implants (and describe)
Steinmann (large diameter, less bend), kirschner wire (smallest diameter steinmann, flex), in the manner of Rush, interlocking nails
Three point fixation- points
1) prox epi/meta cancellous 2) endosteal diaph 3) distal epi/meta cancellous
IM resistance to bend
Proportional to diameter^4th
IM points
Trochar (three sided, sharp); threaded (bounce off), chisel (spaded- trocar goes through bone better!)
IM approaches
Normograde (in end of bone, across fx, into far segment); Retrograde (in fx site, drive prox, then back down to distal)
Easiest to retrieve end of bone config
Tied in (pin through skin, tied to exFix) (vs end cut flush, end cut and countersunk)
Which type of pin are used in the manner of Rush in IM
K wires with chisel tip to deflect
K wire positioning
Less than 15 degrees or less than parallel with medullary cavity
Describe Rush manner
Into cavity, against endosteal cortex, providing dynamic flexion with three point fixation
What IM technique is used in SH fractures
Dynamic pinning- in the manner of Rush, cross proximal to Fx line
Interlocking nails prevent what , due to
Bending, rotational, axial forces due to screw prox and dist to fx line
Femur- preferred IM approach
USUALLY Normo with over=reduction for better distal positioning
Tibia- preferred IM approach
MUST be normo (retro comes out in stifle)
Radius- preferred IM approach
JUST SAY NO (stress pinning of physeal ok)
Ulna- preferred IM approach
either
Humerus
Retro>normo, easier
Requirements for circlage 10 command
Perfect 360 reduction/reconstruction; oblique fx 2-2.5x diameter of bone at Fx level, wire sufficient diameter, more than 1 wire, approp distance (1/5), no soft tissue inside (wire contact bone), perp to long axis (except K), must be tight, prevent slip with hemi or K
Function of cerclage
fragment apposition, not enough stability alone for weight bearing- Always used with plate, pin or exFix
Cerclage forces resisted
dependent on friction of interdigitation
Cerclage wire placement
1cm apart, 5mm from end of segments, evenly spaced
Cerclage- prevent slip at diameter change
Hemi-cerclage (thread through hole in bone); K wire perpendicular to fx, cerclage prox and distal to K wire protrusions
Twist knot- adv/disadv
More resistant to distractive forces, simpler, retighten, cheaper; not as tense as loop, twist protrudes into soft tissue
Loop knot- adv/disadv
Tighter, less trauma from loop, perp to long axis of bone; Less resistant to distractive forces, can’t re-tighten, more $
Biomechanics of loops and twists- 4 studies
Loop greater tension before and after bend; twist lose tension when bent; twist greater distractive resistance, resistance to dist. forces increase with greater wire diameter
Pin and tension band best for
Apophyseal protuberances
Pin and tension band function
Turn tension forces to compressive in osteotomy
Equine limb toe up
P3 (coffin) P2 (pastern) P1 (MCP/fetlock) MC3 (carpus/tarsus-hock) R/U (elbow) Humerus
Primary goal of eq fx
Stabilize limb for transport
Eq- sedation, avoid
Xylazine or detomidine +/- torb (avoid ataxia and acepromzine for a1 antag)
Eq- Section 1 goal
Immob fetlock, align dorsal cortices
Eq- Sec 2 goal
Immob distal to Fx
Eq- Sec 3 goal
Prevent abd
Eq- Sec 4 goal
Carpal extension
Eq- Section 1 bandage and splint
thin nonRJB, dorsal/plantar
Eq- Sec 2 bandage and splint
Thick RJB, Ca/lat (calc to ground)
Eq- Sec 3 bandage and splint
Thick RJB, Ca/lat (elbow/withers or tub cox to ground with wide board)
Eq- Sec 4 bandage and splint
Thin nonRJB, Ca gr to elb; none on hind limb
Eq- Best NSAID for MSkel
Phenybutazone
Eq- transport
Gooseneck or large van - no box or stock
Eq- hindlimb fx face
Front
Eq- forelimb fx face
Back
Eq- Fx Px
type, number, location, open/closed, soft tissue/vasc injury, age/breed/weight/nature, time between injury and intervention, first aid efficacy
Biggest factor for horse prognosis
Type and location
Stall rest indications
non displaced/incomplete stress fx, MC/T 2/4, patella, pelvis
Thomas Schroeder bandage
cast with donut ring- used as a crutch to stabilize
Eq- exFix indication
Distal limb only (fetlock down)
Describe transfixation-pin casts
Spiral around eq leg to dec rotational stress and give axial suppt., 2-3 cross pins prox to Fx in cast to the ground
transfixation-pin casts indications
distal limb
EFSD- describe
U shaped transosseus exFix for distal comminuted
Adv/disadv of eq exFix
Immediate weight bearing, wound/open fx access; only under 90kg or non-weight bearing
4 Principles of Eq intFix
rigid stabilization, anatomic reduction, preserve blood supply, early mobilization (Via screws and plates)
Eq- cortical screws, most common size
Thick with thin thread = strong, rigid; as position, implant, lag fashion; 4.5
Eq- cancellous screw
Thin diameter with thick thread, replace stripped cortical
Eq screw in lag fashion- order
drill (glide) drill (thread) countersink, measure, tap, screw
Eq drill specs
1mm/sec with saline flush to prevent swath overheating/necrosis of bone
Tapping
Creates threaded holes in drilled holes
Plate fixation- eq minimums
4 screws per side of Fx
Eq- DCP- features
Slanted holes, interfrag compression, neutral or compression positions
Eq- LC-DCP- features
same as DCP with scallops and sturdier due to even distribution of mass
Eq- LCP features
more rigid, bigger core, smaller threads, perpendicular only needed, LCP or cortical screws both work, less bone-plate contact bc heads of screws lock in plate= rigid fixation
Eq fx complications
infection, breakdown, osteoarthritis, angular limb deformity, supporting limb laminitis (life threatening)
Princ of intFix
Anatomic reduction, stable int fixation, atrauma, early return to fxn
IntFix screws
self tap- big core, sturdy, creates groove; cancelous- less study but better in cancellous
Locking screws (strength vs cortical)
diam bigger, so stronger
Screw function classification (3)
Implant, lag, position
Implant screw
Most common fxn, hold plate to bone, both cortices preferred
lag screw indications
very oblique fx
position screw
holds in place, no compression, both cortices
Plate classification by function (3)
Compression, neutralization, buttress (bridging)
Compression plate- indication, function, goal
transverse and short oblique; reduce and compress, primary healing
Neutralization plate- indication, function
comminuted, no compression
Buttress plate - indication, function
not reconstructing the column, bridges fx gap and takes on entire load
What plate is the internal external fixator
Locking plates
Minimum cortices in SA plates
4, 6 preferred (3 bicortical or 4 uni+2bi)
Fx fixation specs
Screws 4-5mm from fx line
What fx should not get RJB in SA
femoral and hmeral- fulcrum creation, vessel/tissue tears
When fx takes longer to heal than expected; main causes
Delayed union (>3-4m); bio and mechanical
Bio causes of delayed union
poor blood, infxn, systemic dz, drugs
Mechanical causes of delayed union
inadequate fx fixation causing motion and no callus maturation, poor reduction, excessive post op activity
Dx delayed union-
Rads- distinct fx margins (not rounded), arrest/regression of healing from serial rads
Tx delayed union
Autograft of cancellous, vascularized graft, bone forage, remove implants
Two types of non-union
Viable and non
Dx non-union
palpable instability, mm atrophy, limb deformity
Viable non-unions
hypertrophic callus (lots of blood supply but no healing in middle); slightly hypertrophic, oligitrophic (no callus)
Non-viable unions
dystrophic, necrotic, defect non-union, atrophic non-union
Tx non-union
Just like delayed- Sx- debride, open med canal, rigid fixation, autograft, tx according to type
What type of plate is best for ulna
NONE- too small
Types of mal-union; causes
fxn and non-fxn’l; GP injury, non-anatomic position, poor reduc/stab
Tx mal-union
Corrective osteotomy- realign, rigid rfix
Most common dog infection of implant
Staph
Rad findings in osteomyelitis
Long zone of transition, swelling, sequsterum, avascular/nonviable, involucrum, cloaca
Involucrum
(periosteal rxn around sequestrum, forms membrane
Bandages- change q?
5-7 (can stretch 10 with good compliance)
Prophylactic Abx- schedule
Cefazolon 30-60 min pre-sx; q 1.5-3 h; no more than 24 unless contaminated
