An Insert Goniometer Identifies One Insert Thickness That Provides Maximum Tibial Rotation During Kinematically...

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Biomedical Engineering

Background:

• Kinematically aligned total knee arthroplasty (KA TKA) aims to restore natural knee function.
• The mid-vastus approach for KA TKA allows use of an insert goniometer to determine optimal insert thickness.
• This study investigates the efficacy of the insert goniometer in a medial parapatellar approach for KA TKA.

Purpose of the Study:

• To evaluate if an insert goniometer can identify the optimal insert thickness for maximizing tibial rotation during KA TKA.
• To assess if this method restores full knee extension and enhances knee kinematics.
• To determine the role of insert goniometer in medial parapatellar approach for KA TKA.

Main Methods:

• A medial ball-in-socket and flat lateral insert conformity was used in 33 patients undergoing KA TKA.
• The insert goniometer measured tibial orientation at full extension and 90° flexion.
• Tibial internal rotation was calculated by comparing tibial orientation at these positions.

Main Results:

• The insert goniometer identified specific insert thicknesses (10-14mm) that maximized tibial internal rotation in 33 TKAs.
• Maximal tibial rotation averaged 17 ± 4.1°, significantly greater than with 1mm thinner or thicker inserts (p<0.001).
• The optimal insert thickness varied among patients, highlighting the need for individualized selection.

Conclusions:

• The insert goniometer is a valuable tool for surgeons performing KA TKA via a medial parapatellar approach.
• Utilizing the insert goniometer to maximize tibial rotation restores physiologic knee kinematics.
• This technique, with specific insert conformity, dynamically stabilizes the patella, improving functional outcomes.