General Ortho Flashcards
What are the 2 glycosaminoglycans?
heparin & keratan sulfate
What are the 2 galactosaminoglycans?
chondroitin & dermatan sulfate
Where are the following located?
- Osteoblasts
- Osteoclasts
- Osteocytes
- Osteoblasts: periosteal/endosteal membrane
- Osteoclasts: cortical bone
- Osteocytes: within bone matrix
What is Howship’s lacunae?
resorption pit made by osteoclasts
Hyaline cartilage is made up of what % of the following?
- water
- collagen
- proteoglycan
- glycoprotein
- chondrocytes
- water = 70%
- collagen = 50%
- proteoglycan = 35%
- glycoprotein = 10%
- chondrocytes = 2-10%
What types of collagen are in articular cartilage?
Type II = 85, 90%
Type XI & Type IX
What type of collagen is in fibrocartilage?
Type I
What are Sharpey’s fibers?
dense band of collagen that merges w/ periosteum – where tendons/ligaments insert on bone
(make up the fibrocartilagenous enthesis)
What is a tidemark?
separates non-mineralized and mineralized regions
Write the steps of muscle contraction
AP release ACh –> sarcolemma –> depolarization (Ca2+ release) –> Ca binds to troponin becomes tropomyosin –> exposes myosin on actin –> myosin engages actin –> uses ATP to slide
Type I/II muscle fibers - white or red? Slow or fast?
Type I = SLOW twitch, lots of O2, RED
Type II = FAST twitch, rich myofibers, WHITE
What are the moments of inertia of pin vs. plate?
pin = pi(r)^4 / 4
plate = b(h)^3 / 12
What is the stress formula?
σ = Force / Area
What is the formula for strain?
Epsilon = Δ L / L 0
- epsilon = strain
- delta L = change in length
- L0 = original length
What is Young’s modulus?
on stress/strain curve, it’s initial linear component slope (stiffness!)
What are 2 layers of periosteum?
- Outer - fibroblastoid
- Inner - cambial layer - osteogenic precursors for bone growth
What is the function of the endocortical envelope?
layer of osteoprogenitor cells that regular Ca2+ exchange
Function of cancellous envelope?
ion and nutrient exchange
Function of intracortical envelope?
osteoprogenitor cells that regulate nutrient exchange between vascular system and extracellular space within cortical bone
List 5 zones of epiphyseal plate and main cell type
- Resting - small oval chondrocytes
- Proliferative - stacked coin chondrocytes
- Hypertrophic - new chondrocytes (bigger) *weakest point, very little matrix
- Calcification - chondroclasts remove dead chondrocytes
- Ossification - osteoblasts make woven bone then osteoclasts change woven to lamellar
What fracture line is created with the following forces?
- compressive
- bending
- torsion
- shear
- compressive = oblique
- bending = transverse/short oblique
- torsion = spiral
- shear = buttress
What strain can this tissue survive?
- Granulation tissue
- Fibrocartilage
- Bone
- GT = up to 100%
- fibrocartilage = 10-15% deformation
- bone = 2%
Do smaller or larger fracture gaps have greater strain potential (with similar loads)?
smaller
With contact healing, what is rate of lamellar bone across fracture?
50-100 micrometer / day
For gap healing, how many weeks to have new cutting cones develop new osteons?
3-4 weeks
List 5 stages of bone healing
- Inflammation
- Intramembranous ossification
- Soft callus formation (chondrogenesis)
- Hard callus formation (endochondral ossification)
- Bone remodeling
During bone healing, is electropositivity on convex or concave surface? Primary cell activity?
Electronegativity?
- Electropositive = CONCAVE = osteoclastic
- Electronegative = CONVEX = osteoblastic
For elastic plate osteosynthesis, how can you generate a more compliant structure?
- implant system with lower moment of inertia (e.g. smaller plate)
- implant system with lower modulus of elasticity
- increasing overall length & functional working length of bone plate
List ways that elastic plate osteosynthesis fails
- plate bending from being overly compliant
- fatigue fx of plate (with short working length)
- fatigue failure +/- screw pull-out (too short plate with short working length)
Described classifications of open fractures according to the Gustilo-Anderson scheme
- Type I = wound <1cm, mild ST contusions (inside out)
- Type II = wound >1cm without extensive ST damage (outside in)
- Type IIIa = adequate ST coverage, extensive damage, high energy trauma
- Type IIIb = extensive tissue loss, periosteal stripping, bone exposure, massive contamination
- Type IIIc = open fx with associated arterial injury that needs repair (+ all above in Type III)
What is the interobserver agreement for Gustilo-Anderson open fx classification scheme?
60%
What are the 5 factors of orthopedic trauma association classification scheme?
- S 1-3 = skin defect
- M 1-3 = muscle injury
- A 1-3 = arterial injury
- B 1-3 = bone loss
- C 1-3 = contamination
What are delayed union/nonunion rates for Type I-III open fractures?
Type I = 0-5%
Type II = 1-14%
Type III = 2-37%
What are the diameter and relative tensile strength of orthopedic wire?
- 16g = 1.2mm; 1.4x
- 18g = 1mm; 1x
- 20g = 0.8mm; 0.64x
- 22g = 0.6mm; 0.36x
- 24g = 0.5mm; 0.25x
For twist knot, how many twists to maintain tension?
1
For a single loop cerclage, how many twists need to be in the loop?
1.5
For twist vs. single loop (SL) vs. double loop (DL), list the loop tension and load resisted before loosening
Twist
- Loop tension = 70.3N
- Load resisted = 268 N
SL
- Tension = 165 N
- Load resisted = 259 N
DL
- Tension = 391 N
- Load resisted = 661 N
What are the principles of cerclage?
- choose size for patient
- length of fx should be 2.5x diameter of bone
- should go around entire circumference
- full contact of bone & wire
- 1.5-3 twists for security
- at least 2 wires used
- not used alone for fixation
- only oblique fractures
- space 1/2 bone diameter apart
- place 1/2 bone diameter from fx line
What makes stronger ILN construct?
- fill 80% medullary cavity
- nail with smaller bolts
- bolts that lock to nail
What are the benefits of an angle-stable nail?
- morse taper screw-cone pegs & shape of holes eliminates slack
- stability with forces from several angles
- hour glass shape (improved area moment of inertia & place lock device with larger diameter)
- smaller deformation
Guidelines for sizes of ILNs?
- 3-4mm = cats/dogs 5-15kg
- 6mm = 15-30kg
- 7mm = up to 40kg
- 8-10mm = > 40kg
What diameter of nail for what size of bone?
basically 70-90% of isthmus
When placing ILN, which bolt is placed 1st?
- Tobias says proximal to give stability to alignment guide
- AO handbook says distal 1st so whole construct is stable & easier to place proximal ones after final adjustments
For ILNs, where do you insert for femur, tibia, humerus?
- Femur = intertrochanteric fossa
- Tibia = just cranial to intermeniscal ligament
- Humerus = slight lateral to junction of crest of greater tubercle & greater tubercle
For humerus use of ILN, which parts fractured can be used with regular vs. angle-stable ILN?
- regular = proximal and central only
- angle-stable = proximal and distal
What direction should you place locking device for ILN? Why?
place at 45 degree angle from frontal place in craniocaudal direction
this decreased the risk of hitting brachial and radial nerves
List complications of using ILN
1 = bend, break bit, nail, screw
- radial n paralysis
- “windshield wiper effect” around distal tip
- seromas
- fracture of bone through drill hole
- sciatic n damage
- pain from long screws / bone sequestra
- Lick granulomas
- fx bone near IN
- quadriceps femoris contracture
- coxofemoral luxation
- skin irritation/lesions
- rotational instability
- pseudoarthrodesis
- distal stifle pain
- embolism
- osteomyelitis
- granuloma formation
- superficial wound infection
On the stress/strain curve, which has a higher strain rate - gunshot wound or walking? Which releases greater energy at the fracture?
Gunshot has higher strain rate
WALKING = fracture releases greater energy
Describe 5 types of locking screws
- Threaded head (LCP)
- Cut own threads (Pax securos)
- Bushing & conical taper screw head (Fixin)
- Pearl = SOP with thread at base
- Taper/press fit
With regards to screws, what determines pull-out strength? What determines bending strength?
Pull-out = outer diameter and strength of material
Bending = core diameter
For DCP…
- you can angle the screw to what degrees transverse-wise?
- Angle for longitudinal?
Transverse = 7 degrees
Longitudinal = 25 degrees
For LC-DCP…
- you can angle the screw to what degrees transverse-wise?
- Angle for longitudinal?
Transverse = 7 degrees
Longitudinal = 40 degrees
List some general guidelines for locking plates and screws
- Span long segments of bone (3x fracture length)
- Limit screw-to-hole ration <0.5
- limit distance between plate and bone <2mm
- Leave 2-3 holes empty over fracture defect (1-2 if small gap)
- Screw at end of plate and near fracture
For comminuted fracture - plate length should be ____x the fx length? Simple?
Comminuted = 2-3x
Simple = 8-10x
Why is core diameter larger for locking screws?
Addresses increased stress at screw/plate interface
How much greater insertional torque is there with the Unique Star Drive head?
65%
For plate-rod constructs, every ___% increase in canal filling decreased plate strain by ___%?
10% canal decreases strain by 20%
Total stiffness increases by ___, ___, ___ % with rods filling the medullary canal 30, 40, 50%
6%
40%
78%
For DCP, the gold drill guide is held ___ mm off center for compression. How many mm for green guide?
Gold = 1mm
Green = 0.1mm
For DCP, the 4.5/3.5 plate allows ____ mm displacement per hole.
2.7 plate?
2.4 plate?
4.5/3.5 = 1mm/hole
2.7 = 0.8mm/hole
2.4 = 0.6mm/hole
Smooth pins for ESF inserted up to ___ degrees off from each other to decrease pull-out
70 degrees
Duraface pins: compared to positive profile pins
1. ___% increase in fixation pin stiffness, ____% increase in strength, and ___ fold increase in cyclic failure
55% increase in fixation pin stiffness
54% increase in strength
2.3-4.9 fold increase in cyclic failure
What situations would be useful for use of Duraface?
- smaller segments
- non-load sharing conditions
- biologically compromised bone
- treatment of fracture with large ST envelope (so need longer working length)
List 3 types of ESF clamps
- what are the sizes?
- what bar do they go with?
Titan, Imex (SK), U-clamp
- Large Titan = 9.5mm (3/8” Al or C-fiber)
- Small Titan = 6.3mm (1/4” C-fiber)
- Large U-clamp = 3/16” stainless steel
- Small U-clamp = 1/8” stainless steel
- Large SK Imex = 9.5mm, C-fiber
- Small SK Imex = 6.3mm, C-fiber, titanium
- Mini SK Imex = 3.2mm (1/8”) stainless steel
List materials available to be connecting bars.
Titanium, aluminum, C-fiber, acrylic, stainless steel
Which connecting bars are radiolucent?
Titanium, aluminum, C-fiber
List type, # pins, connecting bar #, and pin geometry for all linear ESF
Ia = half pins, 1 bar, unilateral, uniplanar
Ib = half pins, 2 bars, unilateral, biplanar
I-II = half and 1 full pin, 2 bars, bilateral, uniplanar
II mod = half and 2 full pins, 2 bars, bilateral, uniplanar
II = full pins, 2 bars, bilateral, uniplanar
III mod = half and full pins, 3 bars, bilateral, biplanar
For ESF, what is an articulation vs diagonal?
articulation = interconnecting bars don’t cross fracture gap
diagonal = do cross fracture gap
For a Ib ESF frame, pins can enter the bone up to what angle from each other?
35 degrees
An IN + ESF frame decreases torsional compliance by ___% and bending compliance by ___%?
Torsional = 25%
Bending = 60%
For acrylic ESF, a column of ___mm provides stiffness of 3.2ss and 4.8ss?
9.53mm = 3.2
15.9mm = 4.8
What are the suggested diameters of acrylic columns for ESF?
2-2.5 x diameter of bone and 3-4x diameter of comparable stainless steel bar
How do epoxy and PMMA compare biomechanically to acrylic ESF?
Epoxy - elastic modulus 4x of PMMA
PMMA absorbs 4-6x the energy of epoxy before failure
Epoxy bond with smooth pin = 4x stronger than PMMA and smooth pin
What is knurling?
when you make notches to increase surface area
What are the two names of MMA acrylic? What are set times?
- Acrylx (Imex)
- APEF
12-15min set times
What are the 2 different epoxy resins? Cure time?
- Fastfix (securos)
- Epoxy putty
*Both need catlyst
10-12min cure time
What is the purpose of an Oliver wire?
prevents translation along wires and maintains oblique fracture in compression
what is the purpose of Drop wire?
fixed to ring a distance away from ring using posts to provide 3rd point of fixation along bone
What is a stretch ring?
partial ring with elongated straight segment (horseshoe)
At extreme angles, threaded rods attach via spherical washers and can be angled up to ___ degrees?
10 degrees
What are advantages of ESF over linear ESF?
- tensioned wires = non-linear stiffness response to axial loading
- Low stiffness initially, then increase as load increases
- Allows axial micro motion limited to range gap strain (<2%)
- tensioning - low stiffness micro motion is more like a stiff pin
- cycled between compression/distraction at fracture site to stimulate bone callus maturation
For distraction osteogenesis, how many mm/day do you draw apart the ESF to regenerate bone?
How many days do you wait following osteotomy to start?
1mm/day
3-5 day period of latency
For hybrid fixators, the hybrid adaptor gives ___ degree adjustments for bars?
65 degrees
For hybrid fixators, the VariBall locking hybrid rod permits ___ degrees of angular freedom?
100 degrees
Describe hinged vs. flexible ESF (transarticular)
Hinged
- hybrid connecting bars threaded into female hinges of circular ESF, acrylic connecting bars secured to circular ESF, or joint ROM hinge
- motion limited to single plane
Flexible
- most often for elbow
- 2 central threaded pins parallel to articular surface either side of joint
- pins secured with rigid connecting bars at standing angle of 140 degrees
- once ST swelling decreases, replace C3 with elastics for ROM
How long should rigid transarticular ESF be limited to? Why?
<4 weeks
to limit arthrosis
What are guidelines for ESF associated with
- pin position
- pin #, configuration, size
- insertion
- center of bone
- cis & trans cortex
- 3-4 per bone segment
- 2 for pins & next to joints 1st
- 3/4 bone diameter from joint
- 1/2 bone diameter from fracture line
- aligned parallel along plane of connecting bar (if threaded)
- Smooth/neg profile ~70 degrees from long axis of bone
- clamps 2cm from surface of skin
- pins on either side of connecting bar up to 35 degrees but perpendicular to surface
- pin diameter < or = to 25% bone diameter
- use drill sleeve
- use pretrial (0.1mm smaller than core)
- use low insertion speed (<300)
- use appropriate size connecting bar
- use bone graft
For ESF, pre drilling increases pin tightness ___%, increases pull-out strength ___ % and increased thread contact area ___%
Tightness = 25%
pull-out strength = 13.5%
contact = 18%
What are 6 frame modification techniques for frame destabilization?
- remove augmentation
- remove connecting components
- replace component material
- downsize components
- remove fixation pins
- dynamization clamps
With ESF, what are safe corridors for the humerus, femur, antebrachium, and metacarpal/tarsals?
- Humerus = lateral / craniolateral
- Femur = lateral / craniolateral
- Antebrachium = medial / craniomedial
- Crus = craniomedial
- metacarpal/tarsal = medial/lateral
2nd-3rd = caudomedial to craniolateral
4th-5th = caudolateral to craniomedial
List complications of ESF
- skin trauma/irritation
- impaled muscles/neurovascular structures
- hemorrhage
- peripheral nerve damage
- pin tract infection
- pin/wire loosening or breakage
List 3 other methods of treatment for nonunion / delayed union fractures?
- Extracorporeal shockwave therapy
- Pulsed electromagnetic field
- Low-intensity pulsed ultrasonography
What are the 2 types of osteomyelitis?
- Post-traumatic (most common)
- Hematogenous (young, blood stream)
What are the 3 mechanisms of resistance to antibiotics by biofilm?
- Genotypic & phenotypic alterations
- Extracellular matrix is a barrier preventing Abx penetration
- Extracellular environment affects antimicrobial activity (e.g. pH, paO2)
What is quorum sensing?
ability of bacteria to coordinate gene expression based on population density and role of secreted signal molecules
What is the sensitivity of radiographs to detect osteomyelitis? Specificity?
Sensitivity = 62.5%
Specificity = 57%
For hematogenous osteomyelitis treatment, IV Abx should be given for a minimum of ___ days, then oral for ___ days
IV = 3-5 days
Oral = 21 days
What are the 5 major growth factors that are contributed via bone graft?
- Transforming growth factor B
- Bone morphogenic protein (BMP 2, 4, 7)
- Fibroblast growth factor
- Insulin-like growth factor
- Platelet derived growth factor
What are examples of osteopromotion?
PRP, hydrogels, biphasic CaPO4
List most common sites for acquiring cancellous bone graft
- Proximal humerus
- Wing of ilium
- Proximal tibia
How long should you wait until you can collect graft from the same humerus or tibia?
Humerus = 8 weeks
Tibia = 12 weeks
With autogenous bone graft healing, what is creeping substitution?
cyclical pattern of vascular invasion, subsequent bone formation, resorption
What do allografts lack?
osteogenic cells
