Kinematic comparison between asymmetrical and symmetrical polyethylene inserts during deep knee bend activity

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Knee biomechanics

Background:

• The in vivo kinematic advantage of asymmetrical polyethylene inserts over symmetrical ones in total knee arthroplasty (TKA) remains unclear.
• This study aimed to compare the in vivo kinematics of asymmetrical and symmetrical inserts using the same femoral component design.

Purpose of the Study:

• To analyze kinematic differences between asymmetrical and symmetrical polyethylene inserts in TKA.
• To determine if asymmetrical inserts provide a kinematic benefit, specifically increased axial rotation and posterior femoral rollback.

Main Methods:

• A randomized study comparing TKA with asymmetrical (17 knees) and symmetrical (16 knees) inserts.
• In vivo knee kinematics were assessed using an image matching technique.
• Asymmetrical inserts featured a postero-lateral flat surface, unlike the symmetrical design.

Main Results:

• The asymmetrical insert group demonstrated significantly greater posterior femoral positioning at 70° and 80° of flexion.
• External femoral rotation was significantly higher at 80° of flexion in the asymmetrical group.
• While greater, the increase in femoral rollback and axial rotation with asymmetrical inserts was not statistically significant.

Conclusions:

• Asymmetrical polyethylene inserts may offer a slight kinematic advantage in TKA, characterized by enhanced axial rotation and posterior rollback.
• Further investigation is warranted to ascertain if these kinematic improvements translate to better patient outcomes, satisfaction, and function.