PHII- Ortho > CH41 - Internal fx > Flashcards

CH41 - Internal fx Flashcards

(125 cards)

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1
Q
  • What are the two types of stability and how do they affect healing?
A

Absolute stability
* Interfragmentary compression
* Fragments do not displace under load
* < 2% strain
* < 1 mm gap
* Primary/Direct bone healing

Relative stability
* Bone fragments will displace in relation to each other when force is applied
* Commonly seen in bridge plating
* Secondary/indirect bone healing
* [Image in source document]

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2
Q
  • What is the type of reduction/reconstruction and what category of implant does each require for fixation?
A

Anatomic reconstruction
* Perfect apposition and alignment
* Reconstruction of the bone
* Neutralization implant

Non-anatomic reconstruction
* Comminuted fractures
* Bone cannot share the load
* Buttress (metaphyseal) or bridging implant
* ILN, plate rod, bridging plate

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3
Q
  • What are the methods of reconstruction and when is each used?
A

Open anatomic reconstruction
* Fractures that can have absolute stability → transverse, oblique, spiral, butterfly, segmental, long oblique, minimally comminuted
* Articular fractures

Biologic Osteosynthesis
* Open but do not touch
* Open approach but fracture site is not disturbed
* Reduction performed by using areas of bone away from the fracture or implants - ILN, IM pin

Minimally invasive osteosynthesis
* No open exposure of the fracture
* Minimal approach
* Use of fluoroscopy
* Good for diaphyseal fractures

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4
Q

• What fractures are suitable for anatomic reconstruction?

A

• Transverse
• Short oblique
• Long oblique
• Segmental
• Minimal comminuted w/large butterfly
• Articular fx

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5
Q

• What are the principles of biological osteosynthesis?

A

• Limited fx reduction w/limited approach
• Fracture stabilization using bridging implants rather than anatomic reconstruction and rigid fixation
• Limited reliance on secondary implants
• Limited if any use of grafts

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6
Q
  • What are 2 techniques of biological osteosynthesis
A
  • Open but do not touch
  • MIO
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7
Q

• What is orthopedic wire made out of?

A

• 316 L stainless steel

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8
Q

• What is the tensile strength of orthopedic wire?

A

• Related to cross sectional area = pi x r^2

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9
Q

• What is the weakest point of the wire fixation?

A

• The knot

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10
Q
  • What are 4 uses of wire as an orthopedic implant?
A

Tension band
* Counters tension vector and portion of load is converted to compression

Cerclage
* long-oblique

Hemi-cerclage
* Improves alignment while implant is placed
* IM pin - include in hemicerclage loop so fragments are more tightly braced to the pin
* NOT primary implant, inferior to full cerclage

Interfragmentary
* Ie, maxilla/mandible; anchored around base of teeth
* Relies on bone for stability - must interdigitate

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11
Q
  • List 3 methods of securing wire
A

Twist
* Only 1 loop necessary to maintain tension
* Twisting may damage wire = more susceptible to fatigue failure

Single loop
* Minimum 1.5 twists present in the loop

Double loop
* Wire is folded over on itself to make the loop
* Tightened with wire tightener with two cranks to tighten each wire independently
* Bend the wire over, loosen the crank and cut

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12
Q
  • Name each method of securing wire shown in this image.
A
  • Twist (needs 1 twist to be secure)
  • Single loop (needs 1.5 twists to be secure)
  • Double loop
  • Cable and crimp cerclage
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13
Q

• What is the mode of failure of twisted wire knot vs loop wire?

A

• Twisted - untwisting
• Loop - unbending

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14
Q

• What mode of securing wire resisted the greatest load before being classified as loose (ie, tension <30 N)

A

• Double loop

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15
Q

• By how much tension does the twist knot lose when flattening the knot? Cutting the knot?

A

• 45-90% resting load lost if pushed over to lie flat
• 10N with vibration of cutting

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16
Q

• What % diameter has to be lost for the cerclage wire to be categorized as loose?

A

• 1% = loss of 30 N

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17
Q

• What are the rules of placing cerclage wire?

A

• Long oblique fractures 2.5 - 3 X diameter
• 2 + wires
• Spaced ½ bone diameter apart

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18
Q

• How is cerclage applied to oblique fractures?

A

• Full cerclage can be applied when length of fx is 2.5-3x length of the fracture
• Min. 2 wires
• ½ bone diameter apart
• K-wires and Pins
• [Image in source document]

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19
Q
  • What are the ways that pins are used (name 4).
A
  • Counter rotation - skewer fragments
  • Counter bending - IM pin
  • ESF
  • Spinal sx
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20
Q

• What type of k-wire/cerclage construct resisted torsional forces the most?

A

• 2 k-wires across fracture w/full cerclage anchored around each

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21
Q

• What are the sizes of k-wire available

A

• 0.035 inch (0.9 mm)
• 0.045 inch (1.1)
• 0.062 inch (1.6)

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22
Q

• What are the different tips available for steinmann pins?

A

• 3-faced Trocar
• Diamond
• bayonet

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23
Q

• How is a pin made stronger in resisting bending?

A

• Larger diameter
• Short length
• Area moment of inertia is related to radius^4 = larger diameter is stronger
• [Image in source document]

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24
Q

• If used as the only intramedullary device, what % of the medullary cavity should be filled?

A

• 70%

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25
• If used with a plate what % of the medullary cavity should be filled?
• 35-40%(p. 689)
26
* What are two methods of cross pinning and which is superior in strength?
* Used in physeal fractures * Cross pinning * Superior in strength * Must penetrate trans cortex * Dynamic or Rush pinning - ILN
27
• What forces do ILN resist?
• Bending, rotation, axial load • Via locking mechanism
28
• What are 3 types of ILN in the USA?
• Regular ILN • Dueland • Angle-stable • Dejardin • Inverse Locking Nail • Unger and bruckner
29
* Name these implants.
* Regular ILN attached to aiming device * Screw and bolt for regular ILN * Angle stable ILN with aiming device * Conical bolts for angle stable ILN * Angle stable ILN (hourglass shaped) * Targon ILN
30
• What are 2 locking device options, and what is featured in the current ILN?
• Screws • Bolts • Originally threaded in bone then the nail • 1st gen angle stable - morse taper bolt • 2nd gen - threaded tapered bolts • Screw into shape matched cannulations in the nail = rigid
31
• How much stronger is an 8 mm nail compared to 3.5 mm DCP vs 3.5 mm broad DCP
• 6.8 x • 3.5 x
32
• What is the AMI difference (calc) between plate and a rod?
• Circular radius^4 • Plate thickness^3
33
• Where is the nail the weakest and what modification can be made to improve fatigue life in the ILN?
• Nail is weakest when bending occurs parallel with the screw hole and perpendicular to the long axis • Cannulation of screw hole acted as a stress riser • Methods to make the ILN stronger • Decreasing cannulation ie nail hole size → 3.5 hole to a 2.7 hole increased fatigue life in a 6 mm nail x 52 • Locking bolts = smooth shaft = higher AMI → greater resistance to bending
34
• What is the rate of nonunion in the ILN and what is it caused by?
• 14% • Rotational instability
35
• What improvements or benefits are derived from the angle stable ILN?
• Eliminates rotational and bending instability • Hourglass shape = larger AMI • More conducive to bone healing
36
• What is the optimal fill of medullary cavity with an ILN?
• 80% (no more than 90% isthmus of bone) • 75% of medullary cavity for angle stable
37
• What is slack, and what is the source of slack in ILN?
• Bending of construct when forces applied to it → from mismatch between nail hole and screw diameters, and to deformation of screw threads and nail holes
38
• What are features of angle-stable ILN that overcome instability in bending and torsion as was seen in the regular ILN?
• Hour-glass shaped - larger AMI of prox/distal portion allows locking devices w/greater diameter • Improved vascularity of diaphyseal medullary cavity • Shape of holes + self tapping Morse-tapered locking screw-cone pegs eliminate slack
39
• REgular ILN vs angle-stable ILN compared how in mediolateral and craniocd bending?
• Angle-stable eliminated slack in both bending planes • Angle stable had Smaller maximal deformation • Less interfragmentary motion
40
• What are 2 “modes” of ILN placement?
• Static - secured to both fragments • Dynamic - locked to one fragment; prevents pending, permits load sharing, MINIMAL resistance to rotational deformation; locking prevents migration of implant, some evidence that axial movement at fracture gap improves healing
41
• What are the advantages and disadvantages of dynamization or destabilization of ILN implant?
• Axial micromotion @ gap increased = possible for improved healing • May also prolong healing + second procedure for implant removal
42
• What are appropriate implant sizes for cats/small dogs (5-15 kg) vs small dogs 15-30 kg vs dogs up to 40 kg vs dogs > 40 kg
• 3-4 mm (cats/small dogs) • 6 mm (dogs 15-30 kg) • 7 mm (dogs up to 40) • 8-10 mm (dogs > 40 kg)
43
• Where should the nail be placed in relation to the fracture?
• 2 bone diameters away from fracture line EXCEPT in angle-stable nail
44
• What is most important prior to placement of the nail with regards to the fracture and bone?
• Alignment! • Apposition and reduction not as important
45
• What is the entry portal for femoral ILN? Tibial ILN? Humeral ILN?
• Femoral ILN - proximal flanges through trochanteric fossa → some protrusion as allowed, but not beyond edge to prevent sciatic nerve entrapment • Tibial ILN - 90* flexed, entry cr to the intermeniscal ligament in the sagittal plane, between tibial tuber and medial collateral lig. In the frontal plane • Smaller nails used due to sigmoid curve • Humeral ILN - • Normograde - at/lateral to junction of crest of greater tubercle w/greater tubercle • Directed centrodistally, and seated prox to the supratrochlear foramen • Retrograde - drill retro, limited approach to FX • Locking device distally placed 45* from the frontal plane in cr/cd direction, reduces risk of drill skidding over small epicondylar br. Of radial nerve
46
• What anatomic site should be avoided when placing locking implants in the proximal humerus and why?a
• Tricipital line - avoid w/prox locking devices by going distal or caudal • May increase risk of fx in this area
47
• What are success rates with small animal patients?
• 95%
48
• What is mean time to healing w/angle stable nail placed w/MIO?
• 36 d, range 21-45d
49
• What is the major complication rate for regular ILN vs angle-stable ILN?
• 17% vs 0%
50
* What are the complications noted with ILN?
* Bending or breaking of drill bit, screw, bolt * Osteomyelitis * Radial nerve paralysis * Sciatic nerve damage * Quad contracture * Granuloma at nail tip * Pain * Seromas - PTE * Windshield wiper effect in medullary canal
51
* Name the areas of the screws indicated on this image.
* Core diameter = root diameter * Pitch → the distance between the threads
52
• What is the difference in shaft thread between cortical and cancellous bone screws?
• Cortical → Smaller pitch (ie less distance between threads) and less depth to thread
53
• Why are thread pitches of the locking screw heads half that of the shaft, and why is the pitch finer w/less depth?
• They have double the thread, finer pitch and less depth • Designed to resist bending, less to resist pull out
54
• What is the locking system for LCP?
• Threads on the screw head screw into threads on the plate
55
• What is the locking system for PAX, Scuros?
• Screw head cuts its own thread into protrusions within the plate hole
56
• What is the locking mechanism of fixin systems?
• Threaded bushing • Conical taper
57
• What is the locking mechanisms of the SOP system?
• Thread at base of pearl • Contact ridge w/in pearl
58
• Describe all 4 locking mechanisms and how they work.
• LCP → screw head and plate have threads • SOP → thread on base of pearl and contact ridge • Fixin → threaded brushing and conical taper • PAX securos → cuts its own thread into the plate
59
• What is a shaft screw?
• Partially threaded screw • Non-threaded portion is same diameter of threaded, and thread profile is that of cortical • Stronger in bending • Used for lag in cortical bone
60
• What is a cannulated screw used for and how is it used?
• Used for minimally invasive technique • Can place K-wire first then glide the screw over the k-wire for accurate placement
61
• Why must self-tapping screws be passed 2 mm or beyond the far cortex?
• 2 mm cutting flute at the end decreases SA of bone-screw interface • Must protrude for the bone/screw interface to be as strong as self-tapping screws
62
* Why do bone chip fractures occur on the trans cortex with self-tapping screws?
* When used in hard cortical bone fractures can occur on the trans cortex because the small cutting flukes fill with debris and bone and no longer cut
63
• Torque is converted to _________ due to the shape of the screw threads
• Compression
64
• What dictates the strength of the screw in bending?
• Inner core diameter • This is why locking screws have larger inner core diameter • This is because AMI of screws is · AMI: πr4/4
65
• What dictates the pull out strength of the screw?
• Outer diameter and the material into which it is placed
66
• What are the 3 ways a screw can be placed?
• Lag • Positional • In a plate
67
• What are two ways to place a lag screw?
• Partially threaded screw • Drill glide hole - hole that has the same diameter as the OUTER diameter of the screw on the cis cortex • [Image in source document]
68
• What is the length of oblique fracture min. In order to place an effective lag screw?
• 1.5 x diameter of bone • Any shorter and when placing the screw perpendicular the pieces will shear
69
• What are the principles of positional screws?
• Must engage the cis and trans cortex • Cannot compress or the fragments would collapse • Placed in complex articular fx
70
• What is optimal tightness of a screw compared to stripping torque?
• 70%
71
• Name the screws in this image.
• Cortical • Cancellous • Partial threaded cancellous • Shaft screw • Cannulated screw • Self-tapping cortical screw • [Image in source document]
72
• Is stainless steel 316L more or less stiff than titanium? More or less resistant to fatigue?
• Steel more stiff • Less resistant to fatigue → titanium plates have more resistance to fatigue
73
• What forces do plates resist?
• Bending - only if anatomic reconstruction • Compression • Rotation • Tension
74
• What is the purpose of scalloping on the underside of the LC-DCP plate? (2)
• Minimize stress concentration at the screw hole • Reduces area in direct contact with the bone, less effect on vascularity
75
• What are the screw angles that can be achieved in DCP? How much does the bone displace per hole in compression?
• Hole angles • Longitudinal - 25deg • Transverse - 7 deg • Displacement • 3.5/4.5 → 1mm per hole • 2.7 → 0.8mm per hole
76
• What are the screw angles that can be achieved in LC-DCP? How much does the bone displace per hole in compression?
• Displacement → same • Screw angles → 40/7
77
• How can you strengthen cuttable plates?
• Stacking them on top of each other during placement
78
• What features allow recon plates to be contoured in 3 directions, and stronger or weaker than DCP?
• V in the sides, allow them to be contoured in all 3 directions and softer steel • Weaker than DCP
79
• Pancarpal arthrodesis plate has a _______ degree slope between the surface of the radius and that of metacarpals to reduce need to contour plate
• 5
80
• Where should a semitubular plate never be placed?
• Weight bearing bones - very weak plate
81
• What plate is not designed for compression?
• Cuttable
82
• Name these plates.
• First image • Dynamic compression plates • Second image • A cuttable plate • B Semitubular plate • C Lengthening plates (bridging implant for lengthening or limb spare) • D Reconstruction plate (for oddly shaped bones like pelvis, mandible, maxilla) • Third image • T-plate forpartial carpal arthrodesis plate • carpal arthrodesis plate • acetabular plate (Synthes) • acetabular plate (Jorgensen Lab) • TPO plate (20 deg) • [Image in source document]
83
• What sizes are the acetabular DCP plate available in?
• 2.0, 2.4
84
• What force are plates susceptible to if bone isn’t sharing the load?
• Bending
85
* What are the 4 ways that plates can be applied to bone?
Neutral * Bone shares the load and the fracture has absolute stability and is compressed so the plate is used to neutralize the forces on the bone * Usually done by placing a plate over a lag screw Compression * Bone shares the load and there is absolute stability * Transverse fractures Bridging * Column cannot be reconstructed and there is relative stability → comminuted fractures * Goal is secondary or indirect healing * Plate takes the entire load until callus is formed * With unfilled holes the plate is more susceptible to bending Buttress * Bridge plating at the metaphyseal region
86
• What should be done prior to dcp placement to ensure good contact of the cortex away from the plate?
• Prestressing → this is making the area of the plate over the fracture concave to make sure the cortices on the trans side are touching in simple fractures
87
• What side of the bone should you always try to place the plate?
• Tension side
88
• What will make the plates stronger and resistant to bending and why?
• Reconstructing the bone on the compression side will greatly strengthen the plate on the tension side because the AMI is added to the bone AMI and the whole construct is much stronger • Locking Plates 679
89
• What forces do traditional screw-plate constructs rely on to counteract axial force?
• Axial forces along the bone are converted to shear forces at the bone/plate interface. The shear force is countered by friction between the bone and plate and the torque of the screw.
90
• What forces do LCP use to counteract axial force?
• Shear stress during axial load or bending converted to compressive stress at screw-bone interface due to angle stability • Cortical bone stronger at compressive loads than shear, and loosening of locked screws requires failure of large areas of bone in compression rather the failure of single screw in pull out
91
• Which screw experiences the greatest load in non-locking constructs?
• The one with the greatest screw torque, or whichever one is tightest
92
• If axial force exceeds frictional force at bone-plate interface in conventional plates, strength of the construct depends on what?
• Ability of screw to resist shear, or bone surrounding screws to resist compression • Larger core diameter of screw may allow improved resistance to shear
93
• What is the weakest area of the conventional plate?
• Shear interface between bone and screw
94
• How do conventional plates fail?
• Screws will toggle and loosen and pull out
95
• How do conventional plate/screws resist bending forces?
• Bending stiffness • Resistance of screws to axial pullout (ie, resistance of bone engaged by screw threads to shear)
96
• What are advantages of single beam ie LCP system?
• Decreased dependence on screw strength to resist pull out especially with poor quality bone OR no bone sharing load • Bending loads distributed evenly across whole construct - avoids stress concentration at single screw • Enhances contribution of single monocortical screw
97
• Where is an LCP construct weakest?
• At screw-plate interface; force from strong plate → relatively weaker screw • Purpose for increased core diameter • Improve stiffness by placing plate closer to bone
98
• WHat are minimum number of screws per segment for LCP, and where should they be placed to maximize stiffness?
• 2-3 screws per segment • At end of plate, and near fx zone
99
• What do additional screws, beyond minimum number, contribute to LCP?
• 3rd - increases stiffness if placed toward fx • 4th - increases torsional rigidity • *torsional rigidity not affected by position of 3rd/4th screw
100
• What is the length of the LCP plate that should be used?
• 3 X fracture length
101
• Where should the screws be placed when fx gap is < 1mm? > 6mm?
• < 1mm → place 1-2 holes away from gap • > 6mm → place as close as possible
102
• What is unique about Synthes locking plate?
• Oblong combi hole • One side allows for cortical screw in compression or neutralization but compression in only one direction • Other end features a conical double-start thread for locking screw
103
• What is a “stacked” hole in a LCP?
• A hole at the end of a plate where either a conventional or a locking screw can be placed, but no compression close to a blunt end
104
• Stardrive head allows for applications of ________% greater insertional torque
• 65%
105
• Why use a torque limiter when using power for locking screws?
• To avoid over tightening the screw and cold welding screw to plate
106
• What are the angles of the screws that can be performed in an LCP in longitudinal and transverse?
• L → 40 deg • T → 7 deg
107
• What are 4 techniques used in people to decrease likelihood of plastic deformation and plate failure?
• Plate length >/= 3x fracture segment • Limit screw:hole ratio < 0.5 • Limit distance between plate and bone to <2 mm • Leave last 2-3 screw holes empty over bone defect
108
• Know locking mechanisms of SOP (orthomed), Advanced Locking Plate System (ALPS;Kyon), Fixin System (Intrauma), and Polyaxial System (PAX, Securos)
• Sop • cortical screws thread into plate, press fit screw head and there is a thread at the bottom of the pearl that engages the screw head
109
* ALP locking mechanism
* partial threads in plate hole lock proximal thread of screw, smooth head engages remaining pate hole * Fixin * Threaded bushing and conical head of screw * Insert accommodates morse taper screw head to lock into plate
110
* PAX locking mechanism? Fixin?
* Titanium plate holes have ridges that threaded heads cut unique path into * Does not need to be 90 deg * Can be inserted up to 10 deg of vertical Fixin = conical coupling for locking function
111
• Describe Plate-Span ratio.
• Plate should be 3 X fracture length
112
• Describe plate screw density and what it should be.
• < 50% of the screw holes should be filled with screws • [Image in source document] • Example: 14 hole plate with 6 screws filled = plate screw density of 0.43
113
• What surface is bone plate applied?
• tension
114
* What are 4 applications of a plate?
Dynamic compression * *for short oblique or short transverse only, through eccentrically loaded screws w/in specific plates * Bone shares the load Bridging * Characterized by bone taking all the axial forces * high plate plate:bone length ratio, * low plate screw density < 0.5 * low plate span length (plate:fracture ratio) Buttress * Shore up transcortical defects within metaphyseal regions * Interfragmentary screw commonly used in conjunction with plate * Counters compression and shear forces Neutralization * Shields secondary implants from physiologic loads acting on diaphysis following reconstruction * Bone reconstructed with secondary implants * Long oblique, butterfly, spiral
115
• What is the recommended plate span ratio ie plate:fracture length ratio for comminuted vs simple fx in bridging?
• 2-3x (comminuted) • 8-10x (simple fx)
116
• What is the recommended screw density for plates in bridges?
• 0.4-0.5
117
• What is elastic plate osteosynthesis?
• It is the use of more pliable, less stiff implants in young animals to avoid the pull out at the bone/screw interface that is caused by stiff implants in soft young bone.
118
• What are the principles of EPO?
• Long thin compliant plates • As few screws as possible in each fragment (2 screws and 4 cortices) • Long working length (length between screws and fracture) • This allows for less shear at screw/bone interface because it makes the plate more compliant and increases the elasticity of the plate
119
• What age should EPO be performed at, and why?
• 5-6 mo, >6 mo cortical bone behaves more like mature adult bone • Plate Rod 687
120
• What size should the IM pin be?
• 35-40% canal
121
• What are the forces countered in a plate rod construct?
• Bending in all directions → rod • Axial and rotation → plate
122
• Adding a rod to the construct increases the bending strength by _____ and the fatigue life by ____ fold.
• 2 • 10
123
• By what % did plate strain reduce per each 10% increase in medullary canal fill of rod (30, 40, 50)
• 20% reduction in plate strain
124
• In plate-rod combination, what % of medullary cavity should an IM rod fill?
• 35-40%
125
• How many cortices are required per segment for the screws in a plate rod construct?
• 4 cortices
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