Chapter 45 - Revision Total Hip Arthroplasty

Question 1

Ideal acetabular implant position

Answer 1

30-50 degrees of cup abduction
5-25 degrees of cup anteversion

Question 2

increased dislocation rates in what preoperative diagnoses?

Answer 2

hip fracture
osteonecrosis

Question 3

when can you keep components in a dislocating tha?

Answer 3

when components are in good alignment - treat dislocation with increased head size, dual mobility construct, trochanteric advancement, or constrained acetabular liner

Question 4

what PATIENT factors increase the risk of PJI?

Answer 4

prior hip surgery

DM
Smoking
BMI
Inflammatory Arthritis
Malnutrition
Chronic Immunosuppression

Question 5

what femoral stem malalignment pre-disposes to implant loosening?

Answer 5

varus

Question 6

what factor is most commonly associated with failure to obtain adequate component stabiity?

Answer 6

subsidence

Question 7

what can smaller head size in femoral head resurfacing lead to?

Answer 7

metallosis (<46mm heads)

Question 8

what cell type drives metallosis?

Answer 8

t-lymphocytes

Question 9

what cell type drives osteolysis?

Answer 9

macrophages

Question 10

what has increased head size (>36mm) in THA been associated with?

Answer 10

1. clinical, substantial decrease in dislocaiton rates
2. increased evidence of groin pain
3. higher poly wear rates among younger, more active people
4. corrosion of the head neck junction (increased moment arm)

Question 11

groin or buttock pain indicates what in the presence of a tha?

Answer 11

acetabular cause

Question 12

thigh pain indicates what in the setting of a THA?

Answer 12

stem problem

Question 13

cell counts that indicate infection of acute THA:

Answer 13

27,000 cells/ml
90% pmns

Question 14

cell counts that indicate infection of chronic THA

Answer 14

2500 cells/ml
90% pmns

Question 15

patients with symptomatic metallosis should undergo what imaging study?

Answer 15

MRI metal suppression (MARS)

Question 16

Paprosky classification of acetabular defects

Answer 16

1: focal bone loss, looks like you reamed a primary cup -> porus coated tab with screw fixation
II:
IIa: up and in: (<2cm) - porous cup plus bone grafting
IIb: up and out (<2cm) - porous cup plus augment
IIIc: pure medial migration <2cm, bone grafting, lots of screws porous cup
III:
IIIa: up and out >2 cm -> cup plus graft plus augments
IIIb: pelvic discontinuity -> flange, cup cage

Question 17

when to cement the acetabular component?

Answer 17

bone quality that will not support press fit (even with tons of bone grafting) -> previous irradiation, massive osteolysis

Question 18

late instability with THA most commonly comes from what?

Answer 18

bearing surface wear

Question 19

in the setting of concomitant lumbar fusion and tha what increases the risk of dislocaiton

Answer 19

number of fused levels

Question 20

what combination of implants is mOST associated with trunnionosis

Answer 20

cobalt chromium head, flexible titanium stems