Kinematic alignment of current TKA implants does not restore the native trochlear anatomy

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device design

Background:

• Preserving native patellofemoral anatomy is crucial for physiological kinematics and preventing complications after total knee arthroplasty (TKA).
• Kinematically aligned TKA (KA TKA) aims to replicate natural knee motion, but prosthetic component fit can impact outcomes.
• The Persona femoral component's ability to match native trochlear anatomy in KA TKA requires investigation.

Purpose of the Study:

• To compare native and prosthetic trochlear anatomy after kinematically aligned TKA (KA TKA) using the Persona femoral component.
• To evaluate the safety and effectiveness of using larger Persona component sizes to address understuffing of the native lateral trochlea facet.
• To assess the risk of overstuffing and implant overhang with different KA TKA techniques.

Main Methods:

• Virtual kinematically aligned (KA) and alternative KA (AT KA) techniques were applied to 3D bone-cartilage models of healthy knees.
• Persona femoral component models were virtually implanted using conventional and alternative KA techniques.
• Postoperative bone-implant models were analyzed to compare native and prosthetic trochlear surfaces and mediolateral implant overhang.

Main Results:

• Both planned and implanted Persona trochleae in KA TKA were found to be more valgus oriented and proximally understuffed compared to native anatomy.
• The alternative KA technique (AT KA TKA) demonstrated a high rate of native trochlea surface overstuffing and mediolateral implant overhang.
• Conventional KA TKAs with anterior femoral cut flush showed no overstuffing.

Conclusions:

• Restoring native trochlear anatomy with current Persona implants in KA TKA is not fully achievable, leading to understuffing.
• Increasing component size to match native lateral facet height results in significant overstuffing and overhang.
• Current practice favors undersizing implants in KA TKA, despite not restoring native anatomy, as it may minimize complications; further research into anatomically designed implants is warranted.