In knee arthroplasty, how is malposition of the tibial or femoral component detected on radiographs and corrected?

• A. Look for varus/valgus alignment, slope, rotation; correction may involve revision of the affected component or intraoperative realignment.
• B. Only look for fracture lines; correction is not possible.
• C. Malposition is detected by ultrasound; corrected by medication.
• D. There is no method to assess malposition postoperatively.

Answer: (A)

Postoperative radiographs are used to assess where the knee implant sits in relation to the bones in multiple planes. Malposition shows up as measurable misalignments: in the coronal plane as varus or valgus of the limb indicating the components aren’t aligned with the mechanical axis; in the sagittal plane as an abnormal tibial slope or femoral flexion/extension orientation on lateral views; and rotational issues can be inferred from the relationship of femoral and tibial components to anatomical landmarks. When such malposition is detected and is clinically relevant (pain, instability, abnormal wear, or loosening), the typical correction is surgical revision to reposition or replace the affected component, sometimes accompanied by intraoperative realignment or soft-tissue balancing to restore proper knee kinematics. Ultrasound or looking only for fracture lines won’t reliably reveal the prosthetic misplacement, and a method to assess malposition postoperatively does exist, so those options aren’t accurate.