DOES TOTAL KNEE REPLACEMENT MODIFY FLEXION AXIS OF THE KNEE ON FRONTAL AND AXIAL PLANE REGARDLESS FROM LIMB...

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Medical Imaging

Background:

• The optimal rotational positioning of the femoral component in total knee replacement (TKR) remains a subject of debate.
• Navigational systems offer potential for intraoperative acquisition of patient-specific kinematics and the functional flexion axis (FFA).

Purpose of the Study:

• To prospectively investigate if pre-operative FFA in osteoarthritis (OA) patients with varus alignment changes after TKR.
• To determine the correlation between post-operative FFA and pre-operative limb alignment.

Main Methods:

• A navigated TKR was performed on 108 patients.
• Passive joint kinematics were acquired using specialized software before and after TKR through a 0° to 120° range of motion.
• The functional flexion axis (FFA) was computed using the mean helical axis algorithm, with angles relative to the surgical transepicondylar axis (TEA) measured on frontal (αf) and axial (αa) planes. Pre- and post-operative hip-knee-ankle (HKA) angles were also determined.

Main Results:

• Post-operative FFA differed from pre-operative FFA significantly only on the frontal plane (αf); no significant difference was observed on the axial plane (αa).
• No correlation was found between pre-operative HKA and pre-operative αa.
• A significant correlation was identified between pre-operative HKA and pre-operative αf, indicating frontal plane FFA is dependent on limb alignment.

Conclusions:

• Total knee replacement modifies the functional flexion axis (FFA) solely in the frontal plane.
• The axial plane FFA is not influenced by the degree of varus deformity or the TKR procedure.
• Pre-operative limb alignment is a determinant of the frontal plane FFA, which is positioned more varus relative to the surgical transepicondylar axis before TKR.