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Tobias ECVS - Krizia > Ch 59 - Surgical Management of Hip Dysplasia > Flashcards

Ch 59 - Surgical Management of Hip Dysplasia Flashcards

1
Q

What kind of “joint” is the pelvic symphysis?

A

A synchondrosis which transforms over time to become a synostosis

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2
Q

Which end of the symphysis is larger?

A

Ischial portion is slightly larger

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3
Q

What kind of cartilage makes up the pelvic symphysis?

A
  • Hyaline cartilage - acts as the growth plate
  • Fibrocartilage - gradually replaced by bone
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4
Q

When does the pelvis symphysis start to ossify?
When is it complete?

A
  • Starts to ossify in a caudal to cranial direction beginning at 9-21 months
  • Completely ossified within 2-6yr
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5
Q

List the peripheral ligaments of the pelvic symphysis

A
  • Transverse or oblique fibrous fascia - along the dorsal surface, strengthens
  • Prepubic tendon
  • Arcuate pubic ligament - crosses ischial arch, often becomes ossifies
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6
Q

What is a Juvenile Pubic Symphysiodesis (JPS)?

A

Application of electrocautery to the hyaline cartilage of the pubic symphysis resulting in head-induced necrosis of the germinal chondrocytes and premature closure of the symphysis

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7
Q

How does a Juvenile Pubic Symphysiodesis (JPS) effect acetabular growth?

A

Results in external rotation of the acetabulum in a ventrolateral axial direction, increasing the acetabular coverage of the femoral head

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8
Q

What is the ideal age for Juvenile Pubic Symphysiodesis (JPS)?

A

12 - 20 weeks

25% treated dogs developed OA vs 83% of sham operated dogs

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9
Q

What muscles are partially elevated from the symphysis for Juvenile Pubic Symphysiodesis (JPS)?

A

Gracilis and adductor muscles

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10
Q

What are the recommended electrosurgical settings for Juvenile Pubic Symphysiodesis (JPS)?

A
  • 500kHz current frequency
  • 40W
  • current applied via monopolar probe for 10-30 seconds, every 2-3mm along cranial 1/3 - 1/2 of the symphysis
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11
Q

What are the aims of TPO/DPO?

A
  • Reducing joint laxity
  • Normalising joint stresses
  • Improving joint congruence
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12
Q

What vessels need to be avoided during pubic osteotomy?
Nerve?

A
  • Deeper medial circumflex femoral artery and vein
  • Obturator nerve
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13
Q

What muscles need to be elevated from the ischium for ischial osteotomy of TPO? What structures need to be avoided?

A

Dorsal
- Internal obturator muscle
- Pudendal nerve

Ventral
- Semimembranosus
- Semitendinosus
- External obtruator muscle

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14
Q

What range of angles are typically available for TPO/DPO plates?

A

20 - 45 degrees

The desired degree of rotation is generally 5 degrees greater than the measured angle of subluxation

Coverage by the DAR does not signifcantly increase over that achieved by a 20 degree plate

Rotation beyong 40 degrees is not advised (increases risks of impingement)

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15
Q

What is the reported complication rate after a TPO? What are the main complications?

A

35 - 70%
Screw loosening and pelvic canal narrowing

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16
Q

How have the use of locking plate and DPO effected the rates of screw loosening?

A
  • DPO reduced screw loosening to 3.2% (from 6-36%)
  • Locking plates reduced the rate of screw loosening to 0.4%
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17
Q

How do metallic grains effect THR implant strength?
List manufacturing methods of increasing implant strength

A
  • The smaller the metallic grain, the stronger the implant

Manufacturing methods to srengthen implants:
- Forging
- Investment casting
- Hot isostatic pressing
- Cold working
- Heat working

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18
Q

What is the elastic modulus of stainless steel, cobalt chromium and titanium?

A
  • Stainless steel and cobalt chromium = approx 200GPa
  • Titanium = approx 100GPa
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19
Q

What is stress shielding?

A

Occurs when implant is stiffer than bone, preventing adequate load transfer to the bone, resulting in bone resorption due to relative disuse atrophy leading to implant loosening

20
Q

What metals are in 316L stainless steel?

A
  • Iron
  • Chromium
  • Nickel
  • Molybdenum
21
Q

What metals are in cobalt alloys?
What THR implants use this?

A
  • Chromium
  • Molybdenum
  • Nickel

Implants:
- BioMedtrix BFX anf CFX
- Very hard with excellent wear and corrosion resistance

22
Q

What is the most common titanium alloy?
Which THR implant uses this?

A
  • Ti6A14V
  • Stronger, good fatigue resistance
  • More prone to wear debris than cobalt alloys

Implants
- Zurich Cementless
- Recently switched to Ti6A14Nb

23
Q

What is tantalum?

A

A metal that can be fabricated with a porosity and elastic modulus similar to those of cancellous bone

24
Q

What is tribology?

A

The study of bearing surfaces

The ideal bearing surface is low friction, low wear debris generation, biocompatible, and damage resistant

25
Q

What is the acceptable linear wear rate in people?

A

0.1mm/year

Dogs showed a significatnyl lower volumetric wear that is seen in humans however dogs had a more severe bony reaction (osteolysis) to the debris

26
Q

List the 5 main ways in which wear debris can be generated

A
  • Adhesive wear (cold welding)
  • Abrasive wear (irregularity on surface of harder material or thrid-body wear)
  • Fatique wear (Cyclic loading causing cracks/microcracks)
  • Erosive wear (Solid particle erosion, impingement wear)
  • Corrosive wear (Galvanic corrosion - oxidation that generally results from interactions of dissimilar metals)
27
Q

Under what circumstances is the greatest amount of wear debris created?

A

Titanium bearing surface with a cemented prosthesis

28
Q

List options for coating of metallic heads

A
  • Titanium nitride
  • Diamond-like carbon (“amorphous carbon film”)
29
Q

What are two forms of ceramic used in THR in humans?
What are the benefits?

A
  • Alumina and Zirconia
  • Wear products are locally inert
  • Hydrophilic crating a virtually frictionless fluid-film lubrication
30
Q

What is the reported loosening rate of a Helica implant?

A

37.5%

31
Q

What strategies can be imployed to enhance the strength of the cement mantle?

A
  • Centrifugation and application of a vacuum (Decreases porosity)
  • Pressurisation (injector and intramedullary cement restrictor)
  • Minimum 2mm mantle
  • Femoral stem centralisers
  • Collared prostheses
  • Minimising blood and fat interposition
32
Q

What environment is necessary for bone ingrowth?

A
  • Pore size 50 - 400mcm
  • Micromotion less than 20mcm
  • Porosity of 30-40% is ideal
33
Q

What is the angle of inclination?

A

Angle between the anatomic axis of the femoral neck and femoral shaft
- Lower Femoral neck angle: varus neck
- Higher Femoral neck angle: valgus neck

34
Q

What is femoral offset?

A

DIstance between center of rotation of femoral head and anatomical axis of the femur

35
Q

What is femoral neck anteversion?

A

The cranial angulation of the femoral neck in relative to the anatomical axis of the frontal plane of the femur

Increased anteversion can predispose to craniodorsal luxation

36
Q

What is the goal version angle of the acetabulum?
Goal angle of lateral opening?

A
  • 15 - 20 degrees acetabular retroversion
  • 45 degrees lateral opening
37
Q

What is the recommened version angle of the femoral neck?

A
  • 15 - 25 degrees anteversion
38
Q

What is the overall success rate and complication rate for THR?

A
  • 95% success
  • 5 - 22% complication rate
39
Q

List some forms of mechanical and biological failure of a THR

A

Mechanical
- Luxation (2 - 17%)
- Femoral fracture
- Acetabular fracture
- Acetabular cup avulsion
- Femoral stem avulsion
- Subsidence (less than 4-5mm likely insignificant)
- Implant failure
- Cement failure

Biologic
- Aseptic loosening
- Septic loosening (1 - 2%)
- Stress protection

40
Q

How are THR-related femoral fractures classified?

A

The Vancouver classification:
- Fracture at level of greater trochanter Ag
- Fracture of lesser trochanter Al
- Fracture with stable prosthesis B1 (screw fixation)
- Fracture with unstable prosthesis B2 (press-fit stem)
- Fracture with unstable prosthesis, worse prognosis B3
- C describes fractures distal to prosthesis (cemented stems)

41
Q

What is the “coffin-lid” approach for removing cement?

A
  • Creation of a bone flap starting at base of greater trochanter and extending the length of the cement mantle. Edges should be beveled and corners should be rounded
42
Q

What is the primary cause of aseptic loosening?

A

Wear-debris mediated osteolysis

43
Q

Why is the removal of periprosthetic fibrous tissue a crucial part of revision?

A

Contains mediators of bone lysis
- Activated macrophages
- TNF-a
- Oxygen-derived free radicals

44
Q

What are the reported outcomes of an FHO?

A
  • 38% good (no lameness)
  • 20% satisfactory (some lameness)
  • 42% poor (persistent mild to severe lameness)
45
Q

What are the anatomical landmarks for a FHO?

A

From medial aspect of greater trochanter proximolaterally to lesser trochanter distomedially

46
Q

What are two palliative options for hip OA?

A
  • Hip denervation
  • Pectineus myectomy
47
Q

What muscles need to be elevated from the ischium for ischial osteotomy of TPO? What structures need to be avoided?

A

Dorsal
- Internal obturator muscle
- Pudendal nerve

Ventral
- Semimembranosus
- Semitendinosus
- External obtruator muscle

Tobias ECVS - Krizia (110 decks)

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