PHII- Ortho > CH42- ESF > Flashcards

CH42- ESF Flashcards

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1
Q
  • What are some of the advantages and disadvantages of ESF?
A

Advantages
* Closed reduction
* Dynamization and correction post-op
* Flexibility in configurations
* Adjustable

Disadvantages
* Pin tract infection
* Post-op care
* Bending moments on pins
* Not long term
* Premature loosening
* Owner compliance

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2
Q
  • What were the recommendations for pin placement in linear ESF?
A
  • Place ½ diameter from fracture and ¾ diameter from joint
  • 3-4 pins per segment
  • Place at 90 deg
  • 25% bone
  • Engage trans cortex
  • Farthest first then closest
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3
Q
  • What are the types of pins that can be used in ESF?
A

Smooth steinmann pins
* Prone to loosening, pullout and failure → not recommended

Positive profile pins
* Threads added to shaft
* Greater stiffness, axial pullout strength, fatigue life
* Cancellous → coarser pitch with flatter thread - not for cortical bc microfracture and pull out
* Cortical → thinner pitch with rounded thread → better for ESF

Negative profile pins
* Have threads cut into the shaft so that the core diameter with the threads is smaller than the diameter of the pin
* Originally abrupt transition between threads and smooth area = stress riser
* Gradual transition between threaded and non-threaded portion avoids the stress riser

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4
Q

• What is the recommended diameter for the pins?

A

• Large diameter → more resistant to bending and fatigue
• Large diameter has better hold at the pin/clamp interface

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5
Q

• Name the pins that are shown here and discuss the differences between each of them.

A

• Ellis type negative profile pin
• Threads are cut into the shaft which causes smaller diameter
• Positive profile pin
• Thread applied to the shaft so that the diameter is maintained
• Negative profile pin with tapered thread run-out - Duraface IMEX
• Positive profile pin is overlying the Duraface pin showing that the shaft of the Diraface is larger than the positive profile pin
• [Image in source document]

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6
Q

• How do positive profile pins compare to smooth pins?

A

• Same internal diameter, but cancellous vs cortical threads on one end;
• Greater stiffness, greater axial pull out strength, greater fatigue life

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7
Q

• What is the advantage of the new negative profile pins compared to the older negative profile pins?

A

• Threads + non-threaded portion share same outer diameter
• Tapered transition mitigates stress riser effects
• Maximizes diameter of threaded portion in bone and the diameter of shaft portion outside the bone

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8
Q

• Why is larger shaft diameter desirable? (ie, in negative profile pins)

A

• Greater resistance to bending or failure in cyclic load
• Less likelihood of slippage of pin within the clamp or rotation of the pin around the clamp

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9
Q
  • How do NPP by Duraface with the tapered transition compare to PPP in stiffness, ultimate strength, and cyclic fatigue?
A
  • NPP have 54% increase in strength, 55% increase in stiffness, 2.3-4.9 x increase in cyclic fatigue vs PPP
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10
Q

• What is the difference between half vs full pins?

A

• Half - penetrate soft tissue envelope on one side of bone, engage cis and trans cortex
• Full - penetrate both sides of soft tissue envelope, engaging both cortices (go all the way through the bone and leg)

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11
Q

• Clamps rely on compression of components resulting in what force, which leads to stabilization of the construct?

A

• friction

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12
Q
  • Name the clamps in this image.
A
  • SK clamp (IMEX)
  • TITAN (Securos)
  • Securos U-clamp
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13
Q

• What are the types of connecting bars? (5)

A

• Acrylic (APEF)
• Carbon fiber
• Titanium
• Aluminum
• Stainless steel

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14
Q

• What effect does increasing the size of the connecting bar on pins?

A

• Increases stiffness w/out increasing size of pins
• Decreases load on individual pins → protects the pin bone interface

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15
Q

• Which bars are radiolucent?

A

• Aluminum
• Titanium
• Carbon fiber

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16
Q

• Which is stronger for a given diameter, titanium or carbon fiber?

A

• Titanium 2x as strong as carbon fiber

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17
Q

• How can you strengthen the pin/acrylic interface?

A

• Notches in the pins for greater surface area
• Use pins with knurled shaft

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18
Q
  • Name the bar types.
A
  • Stainless steel
  • Stainless steel
  • Titanium
  • Carbon fiber
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19
Q
  • Name the frames in this image.
A
  • Type Ia → unilateral (one side) uniplanar (one plane)
  • Type Ib → unilateral (one side) biplanar (two planes)
  • Type I-II hybrid (diagonal connecting bar)
  • Type II modified (bilateral uniplanar with half and full pins)
  • Type II (bilateral uniplanar with full pins)
  • Type III (multiplanar)
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20
Q

• What are the methods to augmenting the fixator?

A

• Diagonals - interconnecting bars that span the fracture (figure C above)
• Articulations - interconnecting bars at one end of the bone (figure F above)
• Alternating connecting clamps and pins on either side of a large connecting bar
• Combined frames → combine frames with other fixations like IM pin or ILN

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21
Q

• What are 2 types of augmenting bars and what is their purpose?

A

• Articulations - interconnecting bar at one end of fixator that doesn’t cross the fracture gap
• Diagonals - interconnecting bars that cross the fracture gap
• *add rigidity

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22
Q

• What bar types are amenable to become diagonal bars?

A

• Titanium
• Stainless steel
• NOT carbon fiber

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23
Q

• What do additions of diagonals or articulations do for a hybrid I-II frame?

A

• Add bending, torsional, and axial stiffness

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24
Q

• Where is a I-II frame most commonly placed, and for what fx type?

A

• Humeral and femoral supracondylar fractures

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25
• What type of fixation offers similar result to articulated 1b frame, but is less heavy with only one connecting bar?
• Large diameter connecting bar with connecting clamps oriented on alternating sides of the connecting bar → pins at converging angle, so single bar can support pins that enter up to 35* from each other • [Image in source document]
26
• What is a combined IM-ESF frame and what is the advantage?
• Type IA with IM pin • Pin resists bending and ESF resists compression, rotation and shear
27
• How does T1 ESF w/ IMP compare to TII frame?
• Stiffness modulus similar to that of bilateral frame, • ONLY Moderately lower stiffness in cr-cd bending, and medial-lateral bending, and torsion • *advantage of avoiding to find safe corridors in anatomic location, especially proximally
28
* What is a tie-in configuration and what fracture repairs is it used?
* When proximal IM pin and ESF are connected with a proximal articulation * Prevents migration of IM pin, allows staged destabilization
29
• What effect does ESF -ILN combination have on construct bending, torsion, and compressive loads?
• More resistant to bending, torsion and compression • ESF addition - decreased torsional compliance by 25% • Decreased bending compliance by 60%
30
• What are 2 materials used for acrylic skeletal ESFs?
• Methyl Methacrylate • Epoxy resin
31
• How do acrylic columns compare to stainless steel connecting bars of 3.2 and 4.8 mm diameter?
• 9.54 mm and 15.99 mm = similar to 3.2 and 4.8 in stiffness
32
• What are rules of thumb for thickness of acrylic bar related to the bone, and related to comparable stainless steel bar?
• 2-2.5x diameter of the bone • Should be 3-4x diameter of stainless steel bar to reach similar stiffness
33
• What is a consequence of building a column > 25 mm?
• Excessive heat leads to vaporization, leading to vacuum and potential voids in material which can decrease density and stiffness of a column
34
• How does elastic modulus compare between epoxy and MMA columns?
• Epoxy has 4x elastic modulus vs MMA, but MMA absorbed 4-6 x more energy before failure • Greater elastic modulus of epoxy = 3x stiffer connecting bar compared to comparable stainless steel rod • 9.5 mm acrylic vs 3.2 mm stainless steel
35
• How does MMA columns of 23.35 mm compare to titanium or stainless steel columns?
• 23.25 mm = titanium (6.3 mm) and stainless steel (4.8 mm)
36
• What about central pin shafts has been shown to increase bond between pin and acrylic?
• Knurled interface due to knurled central pin
37
• How much stronger is epoxy bond with smooth pins compared to MMA?
• 40% stronger
38
* Name 2 PMMA products:
* Acrylyx- imex - APEF
39
• Name 2 epoxy resin products:
• FastFix (Securos) • Epoxy Putty (Jorgensen)
40
• How long does MMA take to cure vs epoxy?
• 12-15 min (MMA) • 3-4 min to set, 10-12 to fully cure
41
• How far away should soft tissues be from a 19 mm acrylic column to prevent thermal injury due to exothermic reaction of polymerization/hardening of the implant?
• 1 cm away • Circular Fixator
42
• How does a 1.6 mm wire that is tensioned compare in cantilever bending to a 4 mm pin?
• Equal in strength • [Image in source document]
43
• What types of rings are available for use in ESF? (3)
• Arches - ie, ⅝ arch • Rings - ie, ⅓ ring • Stretch ring - partial ring with elongated straight segments ie horseshoe
44
• What is the primary determinant of frame stiffness for circular ESFs?
• Ring size
45
* What enables wires to resist translation of bone fragments? What is an olive wire? Drop wire?
Placing orthogonal wires at 90* apart * As angle diminishes, ability to resist translation also diminishes Olive wires - stopper rests against cortex * Opposing olives can help with translation Drop wire * Third point of fixation long bone, attached with posts so is distant from actual ring Half pins * Attached to linear pin fixator clamps * *axial micromotion that occurs with fine wire fixation is incompatible with stability rq’d to maintain pin bone interface of conventional pin fixation * Loosen prematurely
46
• What are the connecting elements of a ring fixator?
• Threaded rods and nuts • Spherical washers • Hinges • Adjust angles • Motors or distraction nuts • Move the rings up or down without changing the angle
47
• How much angle do spherical washers add to rings?
• 10*
48
• What structure would allow rings to be angled, and preserve the ability to change the angle?
• Attaching 2 adjacent rings and 2 hinges to a motor = angle between rings becomes relative and can be adjusted • Distraction nuts - allow control ie compression or distraction of fracture or osteotomy site
49
• Why do circular ring fixators exhibit nonlinear stiffness?
• As load increases, the stiffness of tensioned wires increases (does so exponentially) until becomes linear
50
• What do wires allow during movement to stimulate bone healing?
• Micromotion
51
• What determines this property of wires?
• The degree of tensioning determines the amount of micromotion at the fracture
52
• What contributes to and limits axial micromotion for circular ESFs?
• Amount of pre-tensioning - necessary to keep displacement in range that stimulates bone healing rather than inhibiting • Appropriate level of tension is a function of diameter of ring • Diameter of wires limit defection → smaller wires = greater defection and micromotion
53
• What 3 dimensions can bone segments be adjusted and ESF?
• Angulation- ALD • Translation - ALD • Transport - limb lengthening
54
• How should the fixator be placed for ALD correction?
• Place rings perpendicular to bone • Angulation will be highlighted by the rings relationship to each other • Place hinges to hold rings in this position • Hinges should be placed at CORA • Motor is placed between the rings and orthogonal (90 deg) to the axis of the hinges (usually forms a triangle between motor and hinges) - opposite to the vector of deformity • Once the limb is corrected the rings should be parallel to each other • [Image in source document]
55
* What are 3 steps of distraction osteogenesis? How much distraction/day?
1) Osteotomy 2) Latency period - delay of 3-5 days for which hematoma forms at osteotomy 3) Distraction slowly * 1 mm/day → 0.5 mm per 12 hours *rhythm not important * Other resource said younger animals may benefit from more frequent distractions ie q6-8 hours * Also range of mm/d 0.75-2, with younger animals tolerating larger distractions per day compared to older
56
• How is a basic hybrid frame constructed?
• Ring and tensioned wires on juxta-articular bone (next to joint), orthogonally placed • Linear connecting bars • Half pins in the longer bone segment
57
* How is a linear connecting bar stabilized to the ring components? (3)
* Spherical washers and nuts * Allow for 10 degrees of angulation * Hybrid adaptors, ~65* of angulation * Variball locking hybrid rod, ~100 *
58
* Describe/name what is being shown in this image.
* Simple hybrid connected with spherical washers and nuts = 10 deg * Same * Hybrid adaptor = 65 deg * VeriBall locking hybride rod = 100 deg
59
• Where is a stress riser in a hybrid ESF system, and how can this be managed?
• Stress riser at the junction of circular and linear components • Addition of contoured diagonal or articular bar OR • second linear bar → hybrid 1b frame = increase stiffness of simple 1a, decrease stress on frame junction OR • IM pin OR • Addition of half pins OR • Smaller diameter rings = greater resistance to axial compression w/greater overall stiffness of the frame
60
* What are indications (anatomic locations) for hybrid fixators?
* Juxtarticular fractures * Distal humerus * prox/distal antebrachium * Distal femur * prox/distal ends of the crus * tarsal/metatarsal injuries - ALD, arthrodesis
61
• What are the benefits of hybrid ESF?
• Stabilizing small bone segments with circular ring • Ease of application unilaterally • Transarticular ESF
62
• What are 3 types of transarticular ESF frames?
• Rigid - made of 1a triangulated, 1a articulated, or II frame • *>4 wks of immobilization can lead to arthrodesis • Hinged - isometric axis of rotation is debated, can be challenging • Flexible - initially secured at standing angle, then rigid connecting bars replaced with elastic bands to guide controlled ROM
63
• What is a rigid transarticular ESF frame (what types of ESFs can be used)?
• Type 1A • Articulated type 1A • Type II
64
• What happens when a rigid transarticular ESF is left in place for too long?
• > 4 weeks will cause arthrosis • Caused by degenerative cartilage, joint adhesions, soft tissue contracture, degenerative articular changes, loss of ROM
65
• How is a hinged transarticular ESF constructed? What are the benefits? Anatomic locations for use?
• Allows for physiologic load of tendons, ligaments, periarticular soft tissues • Motion of joint in one plane • Circular fixator hybrid with hinged placed at natural axis of the joint • Stifle, tarsus, elbow
66
• What is a flexible ESF and when is it indicated?
• Centrally threaded pins place parallel to joint surface • Adjust the ESF to standing angle • Rigid connecting bars replaced with rubber bands • Uses • Post hip reduction after luxation, elbow instability
67
• What range of motion was allowed with simple circular ESF hinges in the tarsocrural and stifle joint ,and what did joint ROM improve to following removal immediately?
• ROM - 72% (TC), 57% (stifle) • ROM - 84% (TC), 79% (stifle)
68
• What procedure utilized flexible ESF?
• Hip reduction - threaded half pin placed in greater trochanter of femur, directed medially and distal to lesser trochanter; threaded half pin also in illium, and similarly connected with elastic bands to maintain reduction while supporting healing of soft tissues
69
* Describe the safe corridors in two bones (humerus, radius, tibia or femur)
* Green = safe, Yellow = hazardous, Red = unsafe
70
• What is the appropriate pin number and configuration related to prox/distal fracture fragments?
• 3-4 pins per bone segment • Increase pins = Increase stiffness • Order • Far-Far placed first, then attached to connecting bar, • Near - Near • THEN interpositional • *in juveniles, pins should be 1 cm or 3 pin diameters from physis to avoid physeal disruption
71
• How far from adjacent joints and from the fracture line should pins be placed
• ¾ bone diameter away from adjacent joints • ½ bone diameter away from fx line to max bone purchase • The greater the working length in ESF the _______ the stress on the bar. • Greater the stress on the bar
72
• What makes pins stiffer or less stiff in ESF
• Pin stiffness is inversely proportional to pin length • Longer pin = less stiff
73
• How far from the skin must clamps be placed?
• 1cm
74
• What type of frame can divergent pins be placed and how does it impact frame stiffness?
• Applied in a modified T1A, increases axial stiffness and cr-cd bending strength of the frame • Closer connecting bar to bone = greater divergent angle that can be achieved
75
* What is the most common source of weakness or failure in ESF placement?
* PIN BONE INTERFACE - SO IMPORTANT * precise pin placement AND preventing thermal necrosis/mechanical damage
76
• What is the max pin hole size compared to diameter of bone?
• Max 25% of bone diameter - >30% weakens bone and predisposes to fracture
77
• In what 3 circumstances do NPP offer substantial advantages compared to PPP?
• Obese animals with higher BCS • Areas with greater soft tissue mass requiring more working lengths of the pins • Small fragment sizes
78
• What size of drill bit should be used to predrill pin sites?
• 0.1 mm smaller than core diameter of pin being placed
79
• What is the mechanism behind thermal necrosis associated with failure to predrill for pins?
• Friction between debris of bone that cannot be removed w/trocar tip → frictional heat → thermal necrosis→ osteonecrosis → osteoclastic activity = fibrous tissue replacement; excessive stress on fibrous bone = pin loosening
80
• What are benefits of pre-drilling (3)
• Less microcracks • Less thermal necrosis → fibrose bone • Prevents shearing of bone at cis cortex around pin threads when linear mvmt through bone is halted as it hits fresh trans cortex
81
• How much does predrilling increase pin end-insertional torque and pullout strength, as well as thread contact area?
• 25% increase torque, 13.5% pull out strength, 18% thread contact area
82
• What is recommended rpm for pin insertion, and what speeds lead to increase in thermal injury?
• <300 rpm • >700 rpm
83
• At what point in healing can stiff constructs be destabilized in young dogs, adults, and older dogs/cats?
• 4-6 wks - young dogs • 6 wks - adults • 8-10 weeks - old dogs, cats
84
• What is dynamization and how can that be achieved? What is reverse dynamization?
• Removal of pins • Use of dynamization clamps (securos) • The clamps slide along the bar and allow controlled weight bearing • Reverse - increase frame stiffness by adding components • Initially low stiffness promotes healing but in the later stages it can inhibit healing • Clinical Application
85
• What section of humerus is safe to place pins in, and what should be avoided?
• Craniolateral or lateral; avoid intertubercular groove and biceps tendon • Cancellous threaded pins ideal here
86
• Where is ideal distal pin placed through the humerus?
• Avoid lateral distally - radial n. • Transcondylar = ideal • Enters lateral just cr/distal to lateral epicondyle, and exits cr to medial epicondyle, at corresponding point
87
• What should be considered when placing ESF in humerus?
• Medial aspect proximal to lungs • Radial nerve courses laterally over shaft • Types of frames to place in humerus • Type I-II (good for comminuted supracondylar fx) • Hybrid linear circular • IM pin tie in
88
• What are proximal and distal safe corridors in antebrachium?
• Distal → either craniomedial → caudolateral OR medial to lateral • Proxi → craniomedial-caudolateral; or from craniolateral direction (lessen irritation to extensors
89
* What types of ESF in antebrachium?
* Type Ib * Hybrid ring-LESF NO IM PIN
90
• What are quads at increased risk for, and why is this relevant in young dogs?
• Tethering • Quad contracture
91
• What are safe corridors in prox/distal femur?
• Prox- lateral, or craniolateral • Distal - lateral and craniolateral, can do full pin across femoral condyles
92
* What types of ESF can be used in femur?
* Type 1a, I-II, semi-cicrular - Tie in with IM/ILN
93
• What sections of pes/manus should be avoided?
• Palmar, plantar and dorsal
94
• Distal metatarsals/carpals cannot tolerate more than ____ bones pinned together, and which meta bones cannot be combined due to impingement from other metas during weight bearing?
• 2 • 3 and 4 shouldn’t be pinned together • Use 2,3 or 4,5
95
* Types of ESF for pes?
* Acrylic * Circular * IM pin ESF tie-in, SPIDER
96
• What are safe borders for mandible?
• Ventral border - avoid tooth roots and neurovascular structures within mandibular canal • Disadvantage b/c is on compression side, rather than tension side • Types of ESF for the mandible • 1a • Modified type II • [Image in source document]
97
• WHat are the indications and what type of construct can be placed in the vertebral column?
• Small dogs • Fractures, luxations • Biplanar with articulation or spinal arches
98
• What is the recommended pin placement angles and where should they be placed in the spine?
• 45-60 deg from sagittal • Place in vertebral body • [Image in source document]
99
• What are the weakest → strongest constructs in axial and torsion?
• Axial and torsion • 1a<1b<2a<2b<3
100
• What are the weakest → strongest in shear?
• Shear • 1a<2a<2b<1b<3
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