Basic Science Trauma

27 slides

▸ Slide 73 · Basic Science - TraumaBasic Science Trauma · 2 questions expand

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Q1-Q22 questions — tap to reveal all answerslist

What does the Basic Science - Trauma topic cover?
What are the key biomechanical principles of fracture fixation?

Answers · Q & A

Q1.What does the Basic Science - Trauma topic cover?

Not covered in the speaker notes - the slide only carries the section title

Q2.What are the key biomechanical principles of fracture fixation?

Not covered in the speaker notes

▸ Slide 74 · ScrewBasic Science Trauma · 5 questions expand

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Q1-Q55 questions — tap to reveal all answerslist

What is a cable and when is it used?
What materials are used for cables?
What neurovascular and reduction complications can occur with cables, and how are they prevented?
What mechanical complications can occur with cables, and how are they prevented?
Which implants and complications are listed on the slide?

Answers · Q & A

Q1.What is a cable and when is it used?

Device used to exert a circumferential force
For long spiral or oblique fractures

Q2.What materials are used for cables?

Stainless steel / vitallium alloy
Vitallium alloy = 65% cobalt, 30% chromium, 5% molybdenum

Q3.What neurovascular and reduction complications can occur with cables, and how are they prevented?

Neurovascular injury - keep the cable passer close to bone
Loss of reduction intraoperatively or postoperatively - avoid weight bearing / use external bracing

Q4.What mechanical complications can occur with cables, and how are they prevented?

Loosening of cable - tension each cable before locking
Iatrogenic fracture - do not over tension, use a plate to support the cable, gentle reduction especially with rotation

Q5.Which implants and complications are listed on the slide?

Implants: screw, plate, locking plate, DHS, nail, CMN, external fixator
Considerations: fat embolism, compartment syndrome and removal of screws

▸ Slide 75 · K-wire (Kirschner wire)Basic Science Trauma · 5 questions expand

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Q1-Q55 questions — tap to reveal all answerslist

What are K-wires made of and what tip/end designs exist?
What are the functions of a K-wire?
What are the features of a threaded K-wire tip?
What are the features of a trocar K-wire tip?
What are the features of a diamond K-wire tip?

Answers · Q & A

Q1.What are K-wires made of and what tip/end designs exist?

Materials: stainless steel or nitinol (nickel titanium)
Tips: threaded or plain
Ends: trocar / diamond / round

Q2.What are the functions of a K-wire?

Fracture fixation: IM splintage / temporary reduction
Used as a guide wire

Q3.What are the features of a threaded K-wire tip?

Minimises migration
Higher chance of breakage
Better holding than a trocar tip

Q4.What are the features of a trocar K-wire tip?

Worse holding power than threaded
More head generated than threaded (generates more heat than threaded)

Q5.What are the features of a diamond K-wire tip?

Creates larger holes with worse circumferential fit and holding to the bone
Requires less thrust force for bone penetration and generates less heat

▸ Slide 76 · These are screwsBasic Science Trauma · 19 questions 1 check expand

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Q1-Q1919 questions — tap to reveal all answerslist

What is a screw and what is the mechanism of action?
What are the functions of a screw?
What are the features of the head of a screw?
What other head features are described?
What are the features of the shaft of a screw?
Define lead and pitch.
What are the described thread designs?
State the relationships for screw bending and pullout strength.
What tip designs are available for screws?
Compare cortical and cancellous screws.
What is a lag screw?
Describe the design of a cannulated screw.
What are the advantages and disadvantages of a cannulated screw?
Describe the malleolar screw and its pros and cons.
What happens when bone is heated during drilling?
What drill design and drilling technique are recommended?
What is tapping and what are its pros and cons?
How can screw head pressure be reduced?
What factors affect pull out resistance of a screw?

Answers · Q & A

Q1.What is a screw and what is the mechanism of action?

A device which converts rotational motion into linear motion (torque -> linear force)

Q2.What are the functions of a screw?

Compression (interfragmentary / plate to bone)
Positional
Buttress
Polar
Locking bolt / screw

Q3.What are the features of the head of a screw?

(1) Recess engages the screwdriver: hexagonal / star shape / cruciate / Philips / slotted
(2) Arrest forward motion
Threaded (for locking)

Q4.What other head features are described?

Countersink
Runoff

Q5.What are the features of the shaft of a screw?

A core with a spiral surface wrapping around it
Thread may be partial or full
May be cannulated
Root/crest

Q6.Define lead and pitch.

Lead = length the screw travels with a 360 degree turn
Pitch = distance between adjacent threads

Q7.What are the described thread designs?

V-shaped - with shear + compression force
Buttress - resists pull out
Reversed buttress - resists cut out
Thread angle is also described

Q8.State the relationships for screw bending and pullout strength.

Bending strength is proportional to inner (minor) radius ^4
Pullout strength is proportional to outer (major) diameter ^2
Major (outer) diameter determines resistance to pull out

Q9.What tip designs are available for screws?

Standard round tipped
Self tap (fluted)
Self tap self drill
Corkscrew
Trocar

Q10.Compare cortical and cancellous screws.

Cortical: increased core to thread ratio; fine pitch, more threads engaged in cortex, greater pullout resistance (needs more turns)
Cancellous: self-tapping corkscrew tip pushes spongy bone aside to thread its way into bone
Cancellous: increased pitch increases torque needed for insertion; fully or partially threaded

Q11.What is a lag screw?

A screw that gains purchase only over the far cortex

Q12.Describe the design of a cannulated screw.

Replaced the malleolar screw
Low-profile head; Rev-cutting flute (reverse-cutting flute); cancellous thread + self tap; full or half threaded

Q13.What are the advantages and disadvantages of a cannulated screw?

Advantage: precise insertion
Disadvantages: decrease bending and torsional rigidity. Decrease pull out strength (core to thread ratio increased as the core accommodates the guide pin)

Q14.Describe the malleolar screw and its pros and cons.

Trephine tip, smooth shaft and partially threaded
Advantage: trephine tip means no need for tapping
Disadvantages: V shaped screw thread profile (poor holding power), large head and diameter

Q15.What happens when bone is heated during drilling?

Once heat reaches 45 degrees, the mechanical property of bone is altered irreversibly - osteocyte necrosis, ALP deactivation, collagen-HA bone degradation

Q16.What drill design and drilling technique are recommended?

Drill: sharp, straight, with three flutes at 70 degrees (70deg)
Technique: clean tip, drill sleeve, start gradually, maintain angle, use water

Q17.What is tapping and what are its pros and cons?

Tapping: create threads in bone that the screw can enter
Pros: decreases torque to overcome friction, increases torque for holding +/- axial load -> increases pull out strength; less toggling, more precision
Cons: takes longer

Q18.How can screw head pressure be reduced?

Washer
Countersink
Insertion through plate

Q19.What factors affect pull out resistance of a screw?

Screw design: thread diameter (proportional to square of thread diameter) and thread profile
Technique of placement: number of threads engaged (>5 in cortical bone), bicortical purchase, placement parallel to trabeculae pattern
Augmentation with PMMA
Shear load on bone (most important factor)

Fact check

Bone heated to 45 degrees undergoes irreversible alteration of its mechanical properties — imprecise — The widely accepted threshold for thermal osteonecrosis is 47 degrees Celsius for 1 minute (or 50 degrees for 30 s); 45 degrees is used in some studies only as a conservative safety margin — medium confidence — source

▸ Slide 77Basic Science Trauma · 2 questions expand

Question list

Q1-Q22 questions — tap to reveal all answerslist

What topic does this slide belong to?
What implants are used in basic science trauma?

Answers · Q & A

Q1.What topic does this slide belong to?

Not covered in the speaker notes - the slide has no notes or slide content

Q2.What implants are used in basic science trauma?

Not covered in the speaker notes

▸ Slide 78 · These are biodegradable interference screwsBasic Science Trauma · 10 questions expand

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Q1-Q1010 questions — tap to reveal all answerslist

What is an interference fit and what are biodegradable interference screws made of?
Compare the properties of PLA and PGA.
What is the glass transition temperature of PLA and what does it mean?
What are the advantages of biodegradable interference screws?
What load-to-failure values were quoted for bioabsorbable screws versus stainless steel?
What are the disadvantages of biodegradable screws?
Describe the delayed sterile inflammatory foreign body reaction to biodegradable screws.
How do biodegradable screws degrade?
What factors affect the degradation of biodegradable implants?
What is the composition of Biosure Regenesorb and the role of each component?

Answers · Q & A

Q1.What is an interference fit and what are biodegradable interference screws made of?

An interference fit is achieved by shaping the two mating parts so one or both slightly deviate in size from the nominal dimension
Usually made of polylactic acid (PLA) and polyglycolic acid (PGA)
PLA mainly uses the L isomer as it is more stable

Q2.Compare the properties of PLA and PGA.

PLA is hydrophobic and more crystallic (crystalline)
PLA has a longer degradation time (6 months vs 6 weeks for PGA)

Q3.What is the glass transition temperature of PLA and what does it mean?

57 degrees
Below it PLA is rigid and brittle; above it PLA is malleable and rubber-like

Q4.What are the advantages of biodegradable interference screws?

Load to failure similar to stainless steel
No need for removal of implant (ROI)
No artifacts on MRI
Paediatric fracture - can be used as a transphyseal screw
Antibiotics eluting; carrier for growth factors (BMP2/7)

Q5.What load-to-failure values were quoted for bioabsorbable screws versus stainless steel?

PGA/PLLA: 320/300 vs SS 280N (PGA/PLLA 320/300N vs stainless steel 280N)

Q6.What are the disadvantages of biodegradable screws?

Delayed sterile inflammatory foreign body reaction
Expensive

Q7.Describe the delayed sterile inflammatory foreign body reaction to biodegradable screws.

Occurs ~months afterwards, presenting with fluid accumulation / sinus
Culture negative; X-ray shows osteolysis
Consider removal if infected or implant failure

Q8.How do biodegradable screws degrade?

Hydrolysis of ester bonds into small particles, phagocytosed by macrophages and polymorphs
Polymers to monomers, entering the Krebs cycle to CO2 and H2O
Lost mechanical property

Q9.What factors affect the degradation of biodegradable implants?

Crystalline / hydrophobic polymers degrade slower than amorphous / hydrophilic ones (less contact with water)
Starting molecular weight

Q10.What is the composition of Biosure Regenesorb and the role of each component?

65% PLGA
15% beta tricalcium phosphate - sustained bone formation
20% calcium sulfate - early healing

▸ Slide 79 · Tibial nailBasic Science Trauma · 4 questions expand

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Q1-Q44 questions — tap to reveal all answerslist

Describe the AO UTN tibial nail.
What are the special features of the AO UTN tibial nail?
Describe the Stryker GK tibial nail.
Compare the AO UTN and Stryker GK tibial nails.

Answers · Q & A

Q1.Describe the AO UTN tibial nail.

Slot: anterior
Herzog bend: 11 degree, proximal 1/3
Entry: just distal to the tibial articular surface
Cross-section: cloverleaf; material: stainless steel
Proximal: 3 slots - middle dynamic; distal: transverse x2, AP x1

Q2.What are the special features of the AO UTN tibial nail?

Dovetail proximal - increases torsional rigidity
Beveled proximal anterior - decreases irritation to the patellar tendon
Beveled distal posterior - slides smoothly along the dorsal tibial canal, prevents jamming

Q3.Describe the Stryker GK tibial nail.

Slot: posterior
Herzog 15 degrees, proximal 1/5
Entry: just proximal to the tibial tuberosity (TT)
Cross-section: cloverleaf; material: stainless steel
Proximal: transverse x1, AP x1; distal: transverse x2

Q4.Compare the AO UTN and Stryker GK tibial nails.

Slot: AO UTN anterior vs Stryker GK posterior
Herzog bend: AO UTN 11 degrees (proximal 1/3) vs Stryker GK 15 degrees (proximal 1/5)
Entry: AO UTN just distal to tibial articular surface vs Stryker GK just proximal to TT
Both are cloverleaf, stainless steel; AO UTN proximal 3 slots (middle dynamic), distal transverse x2 + AP x1; Stryker GK proximal transverse x1 + AP x1, distal transverse x2

▸ Slide 80 · Describe the nailBasic Science Trauma · 9 questions expand

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Q1-Q99 questions — tap to reveal all answerslist

What is the framework for describing an intramedullary nail?
What are the pros of reaming?
What are the dangers/cons of reaming?
What constitutes proper reaming technique?
What is the working length in a nail and what factors affect it?
Compare bending and torsional working length.
What are the three generations of intramedullary nails?
What are the advantages of interlocking?
How can the rigidity of an intramedullary nail construct be increased?

Answers · Q & A

Q1.What is the framework for describing an intramedullary nail?

Intramedullary nail used for fracture fixation of the femur
Biological reduction + relative stability and secondary bone healing
Describe: longitudinal, transverse profile, material, interlocking, reamed/unreamed
Example given: Stryker GK nail

Q2.What are the pros of reaming?

Decrease working length
Increased width of nail = more rigid
Provides autogenous bone graft
Decreases hoop stress generated - less fracture and breakage of implant than an unreamed nail

Q3.What are the dangers/cons of reaming?

Disrupted blood supply
Thermal necrosis
Pressure -> fat embolism

Q4.What constitutes proper reaming technique?

Patient selection
Equipment: sharp flute with bixcut tip, good clearance by small diameter of flexible shaft keeps pressure low
Technique: slow advancement, high reaming speed, serial increment, venting

Q5.What is the working length in a nail and what factors affect it?

Length of implant spanning the fracture that remains unsupported
Factors: fracture pattern; construct (nail size, bone contact, locking); type of force

Q6.Compare bending and torsional working length.

Bending working length = unsupported area; bending stiffness inversely proportional to square of working length
Torsional working length = distance between locking bolts; torsional stiffness inversely proportional to working length

Q7.What are the three generations of intramedullary nails?

1st gen: internal splint, minimal rotational stability, close fit (e.g. Kuntscher nail / V nail)
2nd gen: locking screw, increased rotational stability (e.g. Russell Taylor nail)
3rd gen: anatomical design for a specific bone, increased stability and easier insertion

Q8.What are the advantages of interlocking?

Increase torsional rigidity
Increase bending rigidity
Control length in comminuted fracture

Q9.How can the rigidity of an intramedullary nail construct be increased?

Reaming to allow a wider nail = more rigid
Interlocking increases torsional and bending rigidity
Decrease working length (more bone contact)

▸ Slide 81 · Kuntscher nailBasic Science Trauma · 6 questions expand

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Q1-Q66 questions — tap to reveal all answerslist

Describe the general design of the Kuntscher nail.
What are the effects of the cloverleaf cross-section of the Kuntscher nail?
What are the effects of the slot on the Kuntscher nail and where is it placed?
What is the principle of fixation of the Kuntscher nail?
What are the advantages and disadvantages of the Kuntscher nail?
What is the indication for a Kuntscher nail?

Answers · Q & A

Q1.Describe the general design of the Kuntscher nail.

Stainless steel
Straight (3-point fixation)
No interlocking
Unreamed

Q2.What are the effects of the cloverleaf cross-section of the Kuntscher nail?

Increases bending stiffness (higher 2nd moment of inertia)
Increases rotational control of the fracture

Q3.What are the effects of the slot on the Kuntscher nail and where is it placed?

Radial compliance -> better interference fit
decrease torsional strength
Place over the tension side

Q4.What is the principle of fixation of the Kuntscher nail?

Tight fitting between the elastic nail and stiff bone
The elastic nail is compressed upon insertion and returns to its original shape, eliminating lateral translation

Q5.What are the advantages and disadvantages of the Kuntscher nail?

Advantage: increased callus (elastic)
Disadvantage - slotted: poor torsional strength
Disadvantage - telescoping: loose axial coupling between nail and bone if not a tight fit

Q6.What is the indication for a Kuntscher nail?

Transverse / short oblique fracture
Minimal shortening
Fracture ends interdigitate - rotation instability

▸ Slide 82 · Centromedullary nailBasic Science Trauma · 5 questions expand

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Q1-Q55 questions — tap to reveal all answerslist

Describe the Stryker GK centromedullary nail.
Describe the old AO UFN design.
Describe the new AO UFN design.
What is the purpose of the dovetail proximal feature on the AO UFN?
Compare slotted and non-slotted nails.

Answers · Q & A

Q1.Describe the Stryker GK centromedullary nail.

Straight nail
GT entry
Cloverleaf cross-section, posterior slot
Proximal: diagonal locking; distal: transverse locking

Q2.Describe the old AO UFN design.

Slot on the anterior side
Entry: piriformis entry
Material: stainless steel
Anterior curve 1.5m
Proximal transverse x2; distal transverse x2
Cross-section: cloverleaf
Special feature: dovetail proximal

Q3.Describe the new AO UFN design.

Unslotted
Entry: piriformis entry
Material: titanium alloy
Anterior curve 1.5/2.0m
Proximal: transverse x2, 130 degree antegrade, spiral blade; distal: transverse x2
Cross-section: grooved
Special: solid, unreamed

Q4.What is the purpose of the dovetail proximal feature on the AO UFN?

Prevents spreading of the proximal end when connected to instruments

Q5.Compare slotted and non-slotted nails.

Slotted nails allow more flexible insertion (at the site and during insertion)
Cloverleaf is usually combined with slotting - radial compliance during insertion allows a bigger nail with maximum 3-point endosteal bone contact, decreasing working length -> increasing bending stiffness
Cons of slotting: poor torsional stiffness (40x), difficult targeting during distal locking

▸ Slide 83 · Cephalomedullary nailBasic Science Trauma · 7 questions expand

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Q1-Q77 questions — tap to reveal all answerslist

What type of nail is the Gamma nail and what is its indication and material?
Describe the frontal, side and cross-sectional geometry of the Gamma nail.
What are the locking features and technique for the Gamma nail?
Describe the design features of the sliding hip screw.
What is the role of the set screw in a cephalomedullary nail?
What type of nail is the Russell Taylor nail and what are its general features?
What are the screw holes and entry technique for the Russell Taylor nail?

Answers · Q & A

Q1.What type of nail is the Gamma nail and what is its indication and material?

Third generation anatomical nail
Indication: femur fracture
Material: titanium

Q2.Describe the frontal, side and cross-sectional geometry of the Gamma nail.

Frontal view: tapered distal to the lag screw hole (15.5 diameter, allowing a small incision) and also distally
Frontal view: ML curve 4 degrees
Side view: anterior curve 3.0mm, radius 1.5m
Cross-section: unslotted; cannulated

Q3.What are the locking features and technique for the Gamma nail?

One lag screw proximally
2 distal locking transverse screws (oblong x1 for axial dynamization)
Technique: GT entry, reamed/unreamed

Q4.Describe the design features of the sliding hip screw.

Load transfer with a large thread area
Reverse buttress thread to reduce cut out
Asymm depth of groove (asymmetric depth of groove) -> allows lateral slide only

Q5.What is the role of the set screw in a cephalomedullary nail?

Decreases sliding hip screw rotation
Decreases hip screw medialization

Q6.What type of nail is the Russell Taylor nail and what are its general features?

2nd generation interlocked nail
Indication: femur fracture
Material: stainless steel
Frontal view: straight nail; side view: anterior curve 2.3m
Cross-section: unslotted, cannulated, fluted

Q7.What are the screw holes and entry technique for the Russell Taylor nail?

2 proximal sliding hip screw holes
4 distal locking screw holes
Technique: piriformis fossa entry

▸ Slide 84 · Rush pin on right, enders nail on leftBasic Science Trauma · 8 questions expand

Question list

Q1-Q88 questions — tap to reveal all answerslist

What are the features of the Enders nail?
What is the indication for an Enders nail?
How is an Enders nail inserted in the femur?
What are the complications of Enders nails?
What are the features of the Rush pin?
What is the indication for a Rush pin?
How is a Rush pin inserted in the femur?
What are the complications of Rush pins?

Answers · Q & A

Q1.What are the features of the Enders nail?

Body: flat, C-shaped
Lead end: blunt and bevelled
Drive end: flattened eyelet, perpendicular to the curve

Q2.What is the indication for an Enders nail?

Initially: TOF fracture
Later: narrow canal diaphyseal fracture

Q3.How is an Enders nail inserted in the femur?

MFC entry point, through the medial femoral cortex
To within 1.5cm subchondral to the femoral head
Entry point roof tile
Insert >3 nails (3-point fixation)
Tips fan out in AP and lateral

Q4.What are the complications of Enders nails?

Fall into bone
Back out -> impinge on soft tissue
Joint penetration

Q5.What are the features of the Rush pin?

Circular and straight
Lead end: sharp and bevelled
Drive end: hooked

Q6.What is the indication for a Rush pin?

Narrow canal diaphyseal fracture

Q7.How is a Rush pin inserted in the femur?

+/- prebend if 3-point fixation is needed
Open cortex with a reamer (diameter < nail)
Entry angle <40 degrees
Driven into bone by a driver extractor
Snugly down so the hook grasps the cortex firmly

Q8.What are the complications of Rush pins?

Iatrogenic fracture
Fracture distraction
Loss of reduction

▸ Slide 85 · Plating effect on fracture healingBasic Science Trauma · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

What is the effect of a plate on cortical bone?
Describe the remodelling sequence under a plate.
Compare titanium and stainless steel plates for fracture fixation.

Answers · Q & A

Q1.What is the effect of a plate on cortical bone?

Stress shielding with transient osteopenia under the plate
Implant contact -> cortical bone blood supply affected
First: necrosis upon contact

Q2.Describe the remodelling sequence under a plate.

Second phase: remodelling
At 1 week (1/52): transient osteopenia under the plate (Ocl)
Intramembranous ossification from the plate ends towards the centre

Q3.Compare titanium and stainless steel plates for fracture fixation.

Titanium: less stress shielding, less infection, less stiff, less MRI artifact
Stainless steel: high yield strength, high ultimate tensile strength, high toughness, cheaper

▸ Slide 86 · D1 post femoral # fixationBasic Science Trauma · 11 questions 1 check expand

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Q1-Q1111 questions — tap to reveal all answerslist

What is the clinical picture and concern on this day 1 post femoral fracture fixation?
What is the quoted incidence and mortality of fat embolism?
What is fat embolism syndrome?
How is fat embolism syndrome diagnosed?
What are the MAJOR Gurd's criteria and their timing?
What are the MINOR Gurd's criteria?
What is the mechanical pathophysiology of fat embolism?
What is the metabolic pathophysiology of fat embolism?
What laboratory finding is described in fat embolism?
How is fat embolism syndrome managed?
How is fat embolism prevented?

Answers · Q & A

Q1.What is the clinical picture and concern on this day 1 post femoral fracture fixation?

Clinical photo showing petechiae over the axillary region
History of recent femoral fracture fixation, likely nailing with reaming done
Worry: fat embolism

Q2.What is the quoted incidence and mortality of fat embolism?

30% of polytrauma patients
10% mortality

Q3.What is fat embolism syndrome?

A systemic inflammatory response to embolised fat

Q4.How is fat embolism syndrome diagnosed?

Gurd's criteria: 2 major criteria, or 1 major + 4 minor criteria

Q5.What are the MAJOR Gurd's criteria and their timing?

Cerebral involvement - 6-12 hrs before respiratory signs
Respiratory compromise - 12-72 hrs
Petechiae - 24-36 hrs, non-blanchable, over the upper trunk

Q6.What are the MINOR Gurd's criteria?

Fever
Tachycardia
Retinal involvement
Jaundice
Renal involvement
Fat macroglobulinaemia

Q7.What is the mechanical pathophysiology of fat embolism?

Fat from disrupted bone marrow or adipose tissue is forced into the torn venule in the area of trauma

Q8.What is the metabolic pathophysiology of fat embolism?

Stress -> fat hydrolysed -> fatty acids
Fatty acids cause endothelial damage
Fatty acids are directly toxic to pneumocytes

Q9.What laboratory finding is described in fat embolism?

Chyle in urine

Q10.How is fat embolism syndrome managed?

Preventive and supportive
MV + high PEEP +/- steroid

Q11.How is fat embolism prevented?

Early long bone stabilisation
Reaming precautions

Fact check

Fat embolism occurs in 30% of polytrauma patients with 10% mortality — misleading/outdated — Rates as high as 30% reflect historic fat embolism (fat globules) rather than the clinical syndrome; with early fracture fixation the incidence of fat embolism syndrome is now ~1-11%, while mortality of ~10% remains accepted — medium confidence — source

▸ Slide 87 · Plate is a a load-bearing device that is most effective when placed on the tensiBasic Science Trauma · 8 questions expand

Question list

Q1-Q88 questions — tap to reveal all answerslist

Where is a plate most effective and what is the working length of a plate?
How are plates classified by function?
How are plates classified by design?
How do you exert compression with a plate?
Describe how compression is exerted by a 'compression plate'.
What affects the rigidity of a plating construct?
What are the beam formulas relevant to plate constructs?
What are the rod formulas relevant to plate constructs?

Answers · Q & A

Q1.Where is a plate most effective and what is the working length of a plate?

A plate is a load-bearing device most effective when placed on the tension side
Working length = distance between the two screws closest to the fracture on each end

Q2.How are plates classified by function?

Neutralization plate - neutralizes bending and rotational force
Compression plate
Bridging
Buttress - placed at 90 degrees against the deforming force
Tension band

Q3.How are plates classified by design?

Tubular
Reconstruction plate
DCP
LC DCP
Locking

Q4.How do you exert compression with a plate?

Lag screw through plate
Compression plate
Prebend plate - screws from central to peripheral for straight/convex bone, and peripheral to central for concave
Tensioning device

Q5.Describe how compression is exerted by a 'compression plate'.

One screw inserted in neutral, so plate and bone become one unit
Hole drilled eccentrically on the other side of the fracture
Screw inserted, head slides down the edge of the screw hole like an inclined cylinder
Relative movement of bone on this side towards the fracture; gives ~1mm compression

Q6.What affects the rigidity of a plating construct?

Material (stainless steel vs titanium)
SMA (bH3/12)
Mode of application (principles of plating, quality of reduction, working length)
Design of plate and screws (locking, design of screw)

Q7.What are the beam formulas relevant to plate constructs?

Bending rigidity = BH3/12 x Young's modulus
Deflection (bending strain) proportional to length^3
Simple terms: plate construct rigidity is proportional to the 3rd power of thickness; the amount of bending is proportional to length^3

Q8.What are the rod formulas relevant to plate constructs?

Bending rigidity = pi r4/4 x Young's modulus
Torsional rigidity = pi r4/2 x shear modulus

▸ Slide 88 · These are DCP and LC DCPBasic Science Trauma · 7 questions expand

Question list

Q1-Q77 questions — tap to reveal all answerslist

What are the advantages of the LC DCP?
What is a locking plate?
What are the biological and mechanical pros of locking plates?
What are the cons of locking plates?
What are the contraindications to locking plates?
What is the mode of failure of a locking plate?
How does conventional plating fail compared with LCP?

Answers · Q & A

Q1.What are the advantages of the LC DCP?

Less contact (smaller footprint) with bone - preserves blood supply, less necrosis, less bone resorption and stress shielding
Stiffness evenly distributed (DCP tends to bend at the level of the screw hole)
Trapezoid cross section leaves an area for bone growth (broad based bone bridge after removal of plate, less prone to refracture)
'Combi hole' symmetrical on both sides allows compression in both directions

Q2.What is a locking plate?

A plate with a threaded screw hole used with screws with a threaded screw head
Becomes a fixed angle device with angular stability, compared with conventional plating which depends on friction between plate and bone
Can be used in compression mode, buttress mode, or bridging mode as an internal external fixation

Q3.What are the biological and mechanical pros of locking plates?

Biologically: less disruption to blood supply, less dissection, can be MISS
Does not rely on direct contact/friction of the plate to bone
Mechanically less likely to fail by screw pullout (bending and torsional stress shared amongst the entire single beam construct)
Larger polar and 2nd moment of inertia when considering the whole construct; fixed angle device especially useful for osteoporotic bone

Q4.What are the cons of locking plates?

Do not aid reduction
Technically demanding
Expensive
Construct can become too rigid if improperly applied
Less tactile feedback when inserting screws

Q5.What are the contraindications to locking plates?

Simple fracture
Unreduced intra-articular fracture

Q6.What is the mode of failure of a locking plate?

The shearing/ bending/ torsional load is shared amongst the screws. The implant will fail in one unit rather than sequential failure
The implant fails as one unit rather than by sequential failure
LCP is a single beam construct - screws must shear through bone simultaneously

Q7.How does conventional plating fail compared with LCP?

Conventional plating: when subjected to bending force, strength depends on the pull out strength of the individual screw closest to the fracture site
LCP: single beam construct, screws must shear through bone simultaneously

▸ Slide 89 · Pedicle screwBasic Science Trauma · 7 questions expand

Question list

Q1-Q77 questions — tap to reveal all answerslist

What design features give a pedicle screw high pull-out resistance?
What type of screw head does a pedicle screw have?
Describe the proximal (pedicle) portion of a pedicle screw.
Describe the distal (vertebral body) portion of a pedicle screw.
What is meant by a double lead (double start) design in a pedicle screw?
What is the transition zone between the proximal and distal screw designs?
What are the handling features of a pedicle screw?

Answers · Q & A

Q1.What design features give a pedicle screw high pull-out resistance?

Dual core design with bone specific anchorage
Double lead (lead = 2 x pitch)
Proximal cortical and distal cancellous thread designs

Q2.What type of screw head does a pedicle screw have?

Polyaxial screw head

Q3.Describe the proximal (pedicle) portion of a pedicle screw.

Cortical screw design: large core, low and broad thread
Gives high strength and tight grip in dense cortical bone

Q4.Describe the distal (vertebral body) portion of a pedicle screw.

Cancellous screw design: small core, high and thin thread
Large surface area allows even load distribution

Q5.What is meant by a double lead (double start) design in a pedicle screw?

Double lead (double start) = lead is 2 x pitch
This contributes to the screw's high pull-out resistance

Q6.What is the transition zone between the proximal and distal screw designs?

Short transition zones between the two designs
A smooth link between the cortical and cancellous portions

Q7.What are the handling features of a pedicle screw?

Self-tapping and self-centering
Blunt tip without a sharp cutting edge for safe handling

▸ Slide 90 · Ideal working length of a bridge plate = at least twice that of the fracture lenBasic Science Trauma · 1 question expand

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Q1-Q11 questions — tap to reveal all answerslist

What is the ideal working length of a bridge plate?

Answers · Q & A

Q1.What is the ideal working length of a bridge plate?

At least twice the length of the fracture
Working length : fracture length ratio of at least 2:1

▸ Slide 91 · Tension band (shifting the fulcrum so the system is shifting from a 1st class leBasic Science Trauma · 4 questions expand

Question list

Q1-Q44 questions — tap to reveal all answerslist

What is a tension band?
List the prerequisites for a tension band construct.
Which implants can act as a tension band?
How does a tension band alter loading across the fracture?

Answers · Q & A

Q1.What is a tension band?

A device that converts a tensile force into a compression force
Shifts the fulcrum so the system changes from a 1st class lever to a 2nd class lever

Q2.List the prerequisites for a tension band construct.

Bone must be eccentrically loaded
Opposite cortex intact to withstand compressive forces
Fracture pattern must be transverse and simple
Construct applied on the tension side
Implant must be able to withstand tensile force

Q3.Which implants can act as a tension band?

Tension band wiring is only one type of construct
A plate can also act as a tension band when the criteria are met

Q4.How does a tension band alter loading across the fracture?

Shifts the neutral axis from the mid axis to the plate-bone junction
Axial loading produces pure tension in the plate and pure compression across the fracture line
This bending configuration is used to produce bending close situation to reduce the working length of the plate

▸ Slide 92 · This is a knee spanning external fixatorBasic Science Trauma · 11 questions expand

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Q1-Q1111 questions — tap to reveal all answerslist

What is an external fixator and what are its advantages and disadvantages?
What is the goal of external fixation?
What are the four ways to improve the stability of an external fixation?
How can pins improve the stability of an external fixator?
Explain the near-near far-far principle.
How can rods improve the stability of an external fixator?
How does the construct improve the stability of an external fixator?
How does reduction improve the stability of an external fixator?
How is stability improved in a ring external fixator?
What are the ways to decrease infection in external fixation?
What are the safety corridors for external fixation pins (right side)?

Answers · Q & A

Q1.What is an external fixator and what are its advantages and disadvantages?

External device stabilising the fracture with pins and rods coupled by clamps
Can be used for temporary or definitive fixation
Advantages: minimally invasive, quick application, flexible during construction
Disadvantages: pin tract infection and neurovascular injury during insertion

Q2.What is the goal of external fixation?

Create a stable construct with low shear and torque
High micromotion at the level of the fracture

Q3.What are the four ways to improve the stability of an external fixation?

Pins
Rods
Construct
Reduction

Q4.How can pins improve the stability of an external fixator?

Place pins close to the fracture (near-near) to decrease working length
Span a longer length (far-far) to decrease the moment arm of bending force and bending stress
More pins; larger pins (not to exceed 1/3 of cortical diameter)
Radial preload decreases micromotion-induced loosening and bone resorption
Bicortical purchase, Material (HA coated), reduce thermal necrosis (predrill, cooling)

Q5.Explain the near-near far-far principle.

2 pins are placed close to the fracture to achieve a short working length and better stability
2 far pins over both fragments share out the stress and increase bending and torsional stability

Q6.How can rods improve the stability of an external fixator?

More rods (increase 2SMA) - double stacking
Thicker rods (increase 2SMA)
Rods close to bone decrease the working length of the pins
Material choice

Q7.How does the construct improve the stability of an external fixator?

More planes
More columns
Ring

Q8.How does reduction improve the stability of an external fixator?

Reduction is listed as one of the four ways to improve stability of the external fixation

Q9.How is stability improved in a ring external fixator?

Decrease ring diameter, increase number of rings, decrease ring spacing, inner rings closer to fracture
Increase wire diameter and pretension (up to 130kg); add wires or half pins
Wire crossing at 90 degrees to bone surface (at least >30 degrees)

Q10.What are the ways to decrease infection in external fixation?

Adequate pin tract release
Pin tract care
Sharp drill, H2O (cooling)

Q11.What are the safety corridors for external fixation pins (right side)?

Femur: proximal 7-10 o'clock, distal 7-10 o'clock
Tibia: proximal 10-11 and 1-3 o'clock, middle 12-3 o'clock, distal 1-3 o'clock
Humerus: proximal 9-11 o'clock, distal 7-8:30 o'clock (Distal: 7-830 OC)

▸ Slide 93 · Skin tractionBasic Science Trauma · 2 questions expand

Question list

Q1-Q22 questions — tap to reveal all answerslist

What is skin traction?
What are the indications, weight limits and complications of skin traction?

Answers · Q & A

Q1.What is skin traction?

Not covered in the speaker notes

Q2.What are the indications, weight limits and complications of skin traction?

Not covered in the speaker notes

▸ Slide 94 · Skeletal tractionBasic Science Trauma · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

Describe the entry point and trajectory for a distal femoral traction pin.
Describe the entry point and trajectory for a proximal tibial traction pin.
What is balanced traction?

Answers · Q & A

Q1.Describe the entry point and trajectory for a distal femoral traction pin.

Entry just proximal to the MFE (too proximal risks Hunter canal, too distal risks intercondylar notch)
2-3 fingerbreadths above the superior pole of the patella with the knee extended
Trajectory parallel to the knee joint, medial to lateral
Insert with the knee flexed, then release the ITB to prevent tethering

Q2.Describe the entry point and trajectory for a proximal tibial traction pin.

Entry 2cm distal and posterior to the tibial tuberosity
Too proximal enters cancellous bone; too distal risks CPN injury
Trajectory parallel to the knee joint, lateral to medial

Q3.What is balanced traction?

Traction in line with the femoral shaft
Thigh sling just distal to the fracture to decrease extension by gastro, allow proximal fragment to reduce by gravity
Counterweight is body weight, with a Pearson attachment
End sling allows assisted knee flexion when prolonged traction is expected; prerequisite is stable callus

▸ Slide 95 · Indication for removal of implantBasic Science Trauma · 4 questions expand

Question list

Q1-Q44 questions — tap to reveal all answerslist

What are the indications for removal of an implant?
How do you remove a broken screw?
How do you remove a locking screw cold-welded to a plate?
How are cannulated and solid nails removed?

Answers · Q & A

Q1.What are the indications for removal of an implant?

Infection
Cross joint (implant crossing a joint)

Q2.How do you remove a broken screw?

Vice grip plier if the shaft is exposed
Hollow reamer with a reverse thread conical extraction device

Q3.How do you remove a locking screw cold-welded to a plate?

Use a carbide drill
Separate the head from the shaft
Separate the plate at the level of the screw
Separate the plate slightly away from the screw and use the plate as a T handle

Q4.How are cannulated and solid nails removed?

Cannulated nail: Winquist technique
Solid nail: antegrade, metaphyseal window or retrograde

▸ Slide 96 · What is compartment syndromeBasic Science Trauma · 10 questions 1 check expand

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Q1-Q1010 questions — tap to reveal all answerslist

What is compartment syndrome?
What are the first sign and the late signs of compartment syndrome?
What is the ischaemia time window in compartment syndrome and how is it managed?
What pressure measurements indicate compartment syndrome?
Describe the fasciotomy for thigh compartment syndrome.
Describe the double incision fasciotomy of the leg.
How many compartments are in the foot and how are they decompressed?
How is fasciotomy performed in the arm and forearm?
How many compartments are in the hand and how are they decompressed?
What is the post-fasciotomy management?

Answers · Q & A

Q1.What is compartment syndrome?

A state of reduction in perfusion to tissue contained within a confined space
Can be due to intra-compartmental or extra-compartmental causes

Q2.What are the first sign and the late signs of compartment syndrome?

First sign: pain disproportional to the condition, exacerbated by passive stretching of muscles in that compartment
Late signs are the 6 Ps: pain, paresthesia, paralysis, pale, pulselessness, perinsishingly cold

Q3.What is the ischaemia time window in compartment syndrome and how is it managed?

Orthopaedic emergency - fasciotomy is indicated
>8 hours of ischaemia causes irreversible skeletal muscle damage and nerve axonotmesis

Q4.What pressure measurements indicate compartment syndrome?

Within 30mmHg of diastolic pressure, or 33mmHg absolute pressure
30mmHg as an absolute cutoff, beyond which nerve will have ischaemia
Whiteside method, indicated when the patient is unconscious
Need manometer, syringe and water tube connected by a 3-way stopcock; measure at the level of the compartment, look at the meniscus, measure all compartments

Q5.Describe the fasciotomy for thigh compartment syndrome.

Lateral incision +/- medial (adductor compartment seldom involved)
Incise the fascia lata to decompress the anterior compartment, then retract vastus lateralis
Incise the lateral intermuscular septum to decompress the posterior compartment

Q6.Describe the double incision fasciotomy of the leg.

Medial incision 2cm medial to the tibia decompresses the posterior compartments (saphenous vein and nerve at risk)
Enter superficial posterior compartment, reflect soleus posteriorly to enter the deep posterior compartment
Lateral incision midway between tibia and fibula decompresses anterior and lateral compartments (superficial peroneal nerve at risk)
Look for the anterior intermuscular septum, transverse incision, enter lateral and anterior compartments 1cm anterior and posterior to the septum
Extensive longitudinal incision of the whole leg length

Q7.How many compartments are in the foot and how are they decompressed?

9 compartments: 4 interosseous, lateral, medial, central deep, middle and superficial
3 incisions: 2 dorsal along the 2nd and 4th metatarsals, plus one medial

Q8.How is fasciotomy performed in the arm and forearm?

Arm: lateral incision from the deltoid insertion to the lateral epicondyle
Forearm: decompress the mobile wad, anterior and posterior compartments
Anterior wound: lateral proximally to expose the mobile wad, curved medially to allow more skin coverage for median nerve and tendons
Release the carpal tunnel at wrist level without crossing the skin crease perpendicularly
Posterior wound: from the lateral epicondyle to the DRUJ

Q9.How many compartments are in the hand and how are they decompressed?

10 compartments: 4 dorsal interosseous, 3 volar interosseous, adductor, thenar and hypothenar
Incisions: hypothenar, thenar, and dorsal 2nd and 4th metacarpals, plus mid-axial blind side of the finger

Q10.What is the post-fasciotomy management?

Assess muscle viability
Leave open
Monitor circulation and rhabdomyolysis
Plan wound coverage

Fact check

An absolute compartment pressure of 33mmHg (or 30mmHg) diagnoses compartment syndrome — contested/imprecise — Contemporary guidance uses the delta pressure (diastolic minus compartment pressure) of 30mmHg or less; absolute pressure thresholds alone are not recommended and may cause unnecessary fasciotomies — source

▸ Slide 97 · Classical sequela of untreated acute compartment syndrome developing from advancBasic Science Trauma · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

What is the classical sequela of untreated acute compartment syndrome of the forearm?
Describe the classical posture of the forearm sequela of compartment syndrome.
How is this sequela classified and treated (Tsuge classification)?

Answers · Q & A

Q1.What is the classical sequela of untreated acute compartment syndrome of the forearm?

Develops from advanced myonecrosis and muscle fibrosis of the forearm
FDP and FPL muscles are most vulnerable

Q2.Describe the classical posture of the forearm sequela of compartment syndrome.

Insensate hand
Flexed elbow, pronated forearm, flexed wrist, adducted thumb
Extended MCPJ with flexed IPJ
Intrinsic minus hand

Q3.How is this sequela classified and treated (Tsuge classification)?

Mild (finger flexor): dynamic splint, tendon lengthening
Moderate (finger and wrist flexor): excision of necrotic muscle, neurolysis, tendon transfer (BR to FPL, ECRL to FDP)
Severe (extensor): free muscle transfer

▸ Slide 98 · DHSBasic Science Trauma · 7 questions expand

Question list

Q1-Q77 questions — tap to reveal all answerslist

What is a DHS and when is it used?
Describe the components and key dimensions of a DHS.
Why is the DHS plate screw angle 135 degrees?
What are the contraindications to a DHS?
What factors affect sliding of the DHS?
What are the 4 modes of failure of a DHS?
What are the advantages of a cephalomedullary nail and the registry evidence?

Answers · Q & A

Q1.What is a DHS and when is it used?

Sliding screw plate device for fixation of stable trochanteric fractures or fracture neck of femur with a high Pauwels angle
Material: 316L stainless steel

Q2.Describe the components and key dimensions of a DHS.

Lag screw 12.5, 8; long barrel 38mm, short barrel 25mm, thread 22mm
Minimum sliding 10mm; recommended sliding 25mm (38+22+10=70, so 85mm is the cut-off; Gundel et al. Injury 1995)
Plate has a staggered array of holes to avoid stress concentration and bone splitting

Q3.Why is the DHS plate screw angle 135 degrees?

130 degrees causes too much bending
150 degrees is difficult to insert and risks screw cut out

Q4.What are the contraindications to a DHS?

No posteromedial support
Reverse oblique fracture pattern
No lateral buttress
Subtrochanteric extension

Q5.What factors affect sliding of the DHS?

Plate barrel angle: decreasing the angle makes it less collinear with the joint reaction force, increasing friction at the screw-barrel junction and the bending moment
Screw length: a class 1 lever, so more screw protruding from the barrel generates more friction at the barrel, increasing bending and fatigue failure

Q6.What are the 4 modes of failure of a DHS?

Cutting out of the compression screw from the femoral head
Pulling off of the side plate from the femoral shaft
Dissociation of the sliding compression hip screw from the barrel
Failure of the hip screw itself

Q7.What are the advantages of a cephalomedullary nail and the registry evidence?

Biological: minimally invasive, does not disrupt the haematoma or rely on reaming graft
Mechanical: load sharing, more efficient load transfer, prevents uncontrolled collapse, intramedullary buttress for reverse oblique fractures
Norwegian hip registry (Injury 2013, 2000+ patients): DHS increase reop rate; cephalomedullary nail gives better pain, satisfaction, QoL and mobility
Long vs short nail: similar outcome but short nail has a higher peri-implant fracture rate

▸ Slide 99 · Dynamic condylar screwBasic Science Trauma · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

What are the features of the dynamic condylar screw?
What is the principle behind the dynamic condylar screw?
Why was the dynamic condylar screw abandoned?

Answers · Q & A

Q1.What are the features of the dynamic condylar screw?

95 degree plate barrel angle
2 proximal round plate holes for independent screws to the calcar (6.5mm cancellous screw)

Q2.What is the principle behind the dynamic condylar screw?

Tension band plating
Prerequisite: intact or well reduced calcar acting as a medial buttress
Need to lag the fracture through the plate for absolute stability

Q3.Why was the dynamic condylar screw abandoned?

High rate of failure
Difficult to reduce the calcar and lesser trochanter from a lateral approach
Non locking, no angular stability
Calcar malreduction and loss of medial buttress: compression side of the tension band not restored, extra bending moment causing fatigue failure

FRCS Quiz — private