Arthro Flashcards
5 variables that affect PE wear characteristics
- PE thickness
- should be >8mm - Articular surface design
- higher congruity / contact aurface area –> leads to lower contact stress and better wear characteristics - Kinematics
- knee kinematics
- change them to get most congrous implant - PE sterilization
- Gamma radiation sterilisation in oxygen depleted environment is the best - PE machining
- best with direct-compression molding
Dual mobility THR concept
Combine Chanley Low-Friction principle & McKee Farrar concept:
Increase femoral head-to-neck ratio, reducing risk of dislocation, by facilitating increased range of motion before impingement & maximising jump distance needed for femoral head to separate from acetabular socket
Dual mobility intraprosthetic dislocation (IPD)
Dissociation of the outer PE head from inner femoral head secondary to degeneration of PE retention rim
Femoral head remains in acetabular socket while PE head lies adjacent
Xray: C-shaped bubble
Clinically: acute pain & limb shortening
Revision TKR, with bone defect, wedge vs block:
Wedge
- less bone cut
- less stable (shear force)
Metal block
- more bone cut
- more stable (platform)
Revision TKR, steps:
Steps:
1. Tibial plaform
2. Then, balance knee in flexion (sizing of femoral component)
3. Balance knee in extension
Aim to restore joint line
Principles of revision TKR:
“E3R”
- Exposure
- Extraction
- Evaluation
- Replantation
THR femoral cementing technique:
Generations:
1st: hand mixing, finger packing
2nd: femoral brushing, cement gun, pressurisation with cement restrictor
3rd: vacuum mixing, distal centralizer
4th: proximal centralizer
Grading of cement technique, based on radiographic analysis:
Barrack and Harris grading system:
Grade A:
- complete filling of medullary canal
- “white-out” cement-bone interface
Grade B:
- slight radiolucency of cement-bone interface (<50%)
Grade C:
- radiolucency >50% of cement-bone interface or
- incomplete cement mantles (<1mm in some areas)
Grade D:
- gross lucencies and/or absence of cement distal to tip
4 principles of TKR:
- Preserved joint line
- Restore mechnical axis
- Restore Q angle
- Soft tissue balancing
CPG guideline for DVT prophylaxis?
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