Does total knee arthroplasty modify flexion axis of the knee?

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Knee Osteoarthritis

Background:

• Total knee arthroplasty (TKA) aims to restore knee function and alignment.
• Understanding the functional flexion axis is crucial for predicting TKA outcomes.
• Native limb deformity can influence surgical planning and implant positioning.

Purpose of the Study:

• To investigate changes in the functional flexion axis after TKA.
• To determine the correlation between preoperative functional flexion axis and native limb deformity.
• To assess the impact of TKA on frontal and axial planes of the functional flexion axis.

Main Methods:

• Navigated TKA performed on 108 patients.
• Passive joint kinematics acquired using specialized software (0°-120° range of motion).
• Functional flexion axis computed via mean helical axis algorithm; angles (α(F), α(A)) measured relative to the transepicondylar axis.

Main Results:

• Postoperative functional flexion axis differed from preoperative only in the frontal plane.
• No significant difference observed in the axial plane functional flexion axis.
• Poor correlation found between frontal plane axis and preoperative hip-knee-ankle angle; no correlation in the axial plane.

Conclusions:

• TKA affects the functional flexion axis primarily on the frontal plane.
• Preoperative functional flexion axis is consistently in a varus position relative to the transepicondylar axis.
• Frontal plane functional axis position is influenced by native limb alignment, unlike the axial plane.