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Trauma Conf/Education > Adult Reconstruction > Flashcards

Adult Reconstruction Flashcards

1
Q

What is femoral stress shielding?

A

Proximal femoral bone loss observed over time in the setting of a well fixed implant.

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2
Q

What is spot welding?

A

New endosteal bone growth contacting the porous coating of the implant. Usually seen w/extensively coated stems. Signs of well-fixed cementless component.

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3
Q

What is the main contributor to proximal femoral stress shielding?

A

Stem stiffness (modulus mismatch). Remember Hoek’s law that 2 springs next to each other. More force transmitted through stiffer spring. Thus the stiffer femoral stem takes on more stress and force and wolfe’s law shows us the result. (bone loss with less stress)

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4
Q

What type of loading is usually seen with extensively coated femoral stems?

A

Distal bone loading. (more proximal stress shielding)

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5
Q

What type of loading is seen with proximal pourous coating?

A

Proximal bone loading in metaphysis and proximal diaphysis

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6
Q

What is the major factor contributing to femoral stem stiffness?

A

Stem diameter. The stiffness approximates the radius to the 4th power. Small changes in radius cause exponential increase in stiffness

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7
Q

What is the most common initial presentation in a THA that is failing?

A

Start-up pain. Groin pain may be loos cup, thigh pain loose femoral stem. Must R/O infection

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8
Q

When replacing acetabular cup on revision case, what is ideal position for lowest joint reaction force?

A

Low and inside. (inf and medial)

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9
Q

What is the safe zone for acetabular cup screws?

A

The posterior superior zone. Structures at risk here are sciatic n, sup gluteal n and vessels. This is the recommended zone

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10
Q

What structures are at risk if acetabular cup screws are placed in anterior superior quadrant?

A

Zone of death! Risk laceration to external iliac artery and veins. Avoid this area.

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11
Q

Name the 4 quadrants for screw placement for acetabular cup screws and risks in each.

A
  • Anterior/Sup: Zone of death. Ext iliac art and veins
  • Posterior/Sup: Safe zone. Sciatic n, sup glu art and n
  • Posterior/Inf: Safe if screws
  • Anterior/Inf: Obturator n and vessels. Avoid screws
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12
Q

What is the significane of bone defects (cavitary or segmental) on femoral sided lesions?

A

Revision femoral stem must bypass the most distal cortical defect by a minimum of 2 cortical diameters.

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13
Q

What is the main culprit in osteolysis?

A

PE wear. From 2 sources.

  • PE bearing wear: the head/cup articulation
  • Backside wear: PE insert rubs against metal shell
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14
Q

What type of wear is the most important process that generates sub-micron sized particles?

A

Adhesive wear

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15
Q

What is adhesive wear?

A

Microscopic sticking of the PE to the implant which causes pulling off of the submicron beads from the PE

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16
Q

What is abrasive wear?

A

Cheese grater effect. A rough femoral head caues mechanical scratching of the PE.

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17
Q

What is 3rd body wear?

A

Particles within the joint space that cause abrasion. Some particles could be from cement, metal debris from cup or stem, metal debris from corrosis, hydroxyappetite debris etc.

18
Q

What is the effective joint space?

A

It is any contiguous area around the joint where the implant touches the bone. Incues area around cup, stem and screws. Osteolysis can occur anywhere in this space

19
Q

What is the main determinant of the number of PE particles produced from wear?

A

Volumetric wear. Head size is most important factor in predicting amount of particles.

20
Q

What is the eqution for volumetric wear?

A

V= 3.14r2w (r2 = r squared)

  • r= radius of head
  • w = linear wear = distance the head has penetrated into cup

Smaller head has more linear wear and less volumetric, fails from wear through PE

Larger head is opposite and has more stability. Fails from osteolysis. 28mm head is standard

21
Q

What rate of linear wear is associated w/ osteolysis?

A

>.1mm/yr

22
Q

Osteolytic lesions that appear in first 2-3 yrs of prosthesis often signify what?

A

Infection. Osteolysis usually not present for>10yrs

23
Q

What is the hallmark finding is osteolysis?

A

Endosteal scalloping

24
Q

What is the mechanical axis of the femur?

A

A line drawn from the center of femoral head to the medial tibial spine and from there through the center of the ankle joint

25
Q

What is the mechanical axis of the femur?

A

Line drawn down center of femoral canal and tibial canal through ankle joint. Usually about 6 degrees from anatomic axis.

26
Q

If doing an osteotomy for varus knee alignment, where and what type of osteotomy is performed?

A

Valgus-producing proximal tibial osteostomy

27
Q

For valgus knee alignment, if doing osteotomy, where and what type should be performed?

A

Varus producing supra-condylar femur osteotomy

28
Q

What are some contraindications to unicompartmental arthroplasty?

A
  • ACL deficiency is an absolute contraindiction
  • Fixed deformity not correctable with clinical exam
  • meniscectomy in opposite compartment
  • Inflammatory arthritis
29
Q

What is the Q angle?

A
  • Quadriceps angle. Measured from ASIS to center of Patella and Patella to tibial tubercle.
  • Males 14 deg, females 17 deg
  • Basically the angle between the quadriceps tendon and patellar tendon
30
Q

What is femoral rollback?

A

The progressive posterior change in the femoral-tibial contact point with increasing degrees of knee flexion.

  • Influenced by PCL tension
31
Q

What is “lift off” when refering to PCL balancing?

A

Lift off is when flexing the knee causes the anterior portion of the tibial insert to lift up. Can be fixed by PCL recession

32
Q

What deformities should discourage you from performing cruciate retaining TKA?

A

Valgus >15 deg

Varus > 10 deg

33
Q

How is femoral rollback maintained in cruciate sacrificing TKA?

A

The femoral cam makes contact with the tibial post which allows femoral rollback. The cam and post control rollback

34
Q

What are the 2 types of cruciate sacrificing TKA?

A

Anterior stabilized (extended anterior PE lip)

Posterior stabilized (cam and post)

35
Q

What is sliding wear in TKA?

A

With the ACL removed in a cruciate retaining knee, as the knee flexes there is paradoxical ant sliding which causes PE sliding wear.

36
Q

What is the major contributing factor to “cam jump”?

A

Flexion gap being too loose. Occurs with varus/valgus stress w/ knee flexed

37
Q

What is patellar clunk syndrome and how can it be prevented?

A

Scar tissue superior to patella gets caught in box as knee moves from flexion to ext. (occurs 30-45 deg).

  • Prevent by performing synovectomy and debridement of all scar tissue from quad tendon at time of TKA
38
Q

What is the problem with internal rotation of the femoral component in TKA?

A

Causes patellar groove to face inward and gives relative lateral tilt to patella. Also causes increased and unbalanced flexion gap

39
Q

What is the most common complication after TKA?

A

Patellar mal-tracking. Prevent by reducing Q angle which includes proper placement (rotation and medial/lateralization) of both tibial and femoral components

40
Q

Patellar clunk is unique to what knee design?

A

Post stabilized. Gets stuck in box

41
Q
A

Trauma Conf/Education (7 decks)

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