Which of the following are reasons the provisional AP axis would need to be collected?

• A. If 60 degrees of flexion cannot be collected
• B. If the patient's mechanical axis was outside of 7º varus or 3º valgus
• C. Both of the above
• D. None of the above

Answer: (C)

Collecting a provisional AP axis is used when you don’t have reliable data from your usual landmarks, so you need a temporary reference to guide alignment. If the knee can’t be flexed enough to reveal the native AP orientation—specifically, if you can’t obtain 60 degrees of flexion—the normal flexion-based landmarks can’t be trusted. A provisional AP axis provides a workable reference in that incomplete-data situation.

Similarly, if the patient’s mechanical axis falls well outside normal alignment (more than 7 degrees Varus or 3 degrees Valgus), the coronal landmarks can be distorted by the deformity. Again, a provisional AP axis gives a stable reference point to plan the component orientation while accounting for the abnormal alignment rather than forcing a standard neutral expectation.

So, both scenarios create a need for a provisional AP axis to ensure accurate planning.