Component rotational alignment in unexplained painful primary total knee arthroplasty

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering

Background:

• Rotational malalignment of total knee arthroplasty (TKA) components is a potential cause of poor outcomes, but acceptable limits remain undefined.
• This study investigated rotational alignment in patients experiencing unexplained pain post-TKA compared to a matched control group.

Purpose of the Study:

• To define acceptable rotational alignment limits for components in total knee replacement.
• To identify if component malrotation is associated with unexplained pain after TKA.

Main Methods:

• Comparative analysis of rotational alignment using the Berger protocol and postoperative CT scans.
• Measurement of tibial and femoral component rotations, combined rotations, and component rotational mismatch.

Main Results:

• Internal rotation malalignment of tibial (5.8°), femoral (3.9°), combined (8.7°), and mismatch (5.6°) components was significantly associated with pain.
• No significant association was found between excessive external rotation and TKA pain.
• Painful TKA cohort showed internal rotation, while the control cohort exhibited external rotation.

Conclusions:

• Internal rotation malalignment of individual components, combined rotation, and component mismatch are factors contributing to pain after TKA.
• External rotation of components was not identified as a cause of pain in TKA.
• This research provides specific internal rotation limits for Nex Gen Legacy LPS flex fixed bearing TKA associated with pain.