Rotational Alignment

Mechanical causes are present 30–50% of the time in cases of early failure, with specific causes including:
- patellofemoral maltracking,
- instability,
- stiffness
- malalignment of components
Rotational profile has an impact on
- flexion gap
- stability in flexion
- patellofemoral
- tibiofemoral joint kinematics
Malrotation may lead to problems
- cam-shaft impingement
- altered polyethylene loading and wear
- patellar subluxation, dislocation
- loosening
internal rotation of the femoral component
- leads to
  - malalignment of the trochlear groove relative to the patella.
  - flexion gap asymmetry with a medial smaller flexion gap
    - causing an imbalance in soft tissues with increased tightness of the medial-sided structures and lateral-sided laxity.
Internal rotation of the tibial component
- leads to
  - relative external rotation of the tibia and tubercle
    - causing an increased Q angle

External rotation of the femoral component leads to a rectangular flexion space when the tibia is resected at 90 degrees relative to its anatomic axis
Options
- transepicondylar axis
  - medial sulcus to the lateral epicondyle
- Whiteside line
  - lowest point in the sulcus of the distal femur to the center of the intercondylar notch
- posterior condylar axis
  - varies with the difference in cartilage thickness between the medial and lateral condyles
- gap technique