- Sizing of the Tibial Component:
- generally, the tibial component is either the same size as the femoral component or is one size lower;
-
rotation of tibial component:
- avoid internal rotation of the tibial component:
- medially rotated tibial &
femoral components have a high incidence of assoc postop patellar dislocation;
- if there is tendency for lateral subluxation, position of tibial component can be adjusted to more external
rotation, producing relative internal rotation of tibial tubercle, lessening angle between quadriceps &
patellar tendon, & thus lessening tendency of patella to dislocate laterally; (see Q angle);
- note that too much external rotation of the tibial component can overhang laterally and cause impingement on the popliteus tendon;
-
medial lateral translation:
- goal is to provide maximum coverage &, when possible, have component extend to the cortical margins;
- laterally dislocated soft tissues tend to push trial component medially, which is resolved by adequate retraction;
- medial overhang is unacceptable;
- slight lateral translation of the tibial component helps to centralize patellar tracking;
-
anterior posterior translation:
- goal is to provide maximum coverage;
- if symmetric component is sized to fit AP length of medial plateau, comonent will either overhang
posteriorly on the lateral plateau or have a tendency to
internally rotate;
- the solution is to compromise in AP coverage, rather than allow overhang or internal rotation;
- appropriately sized component is then placed as posteriorly as possible;
- this will in effect shift the tibial tubercle anteriorly, which will decrease patello-femoral contact pressures;
