Differences in trochlear parameters between native and prosthetic kinematically or mechanically aligned knees

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical imaging

Background:

• Total knee arthroplasty (TKA) aims to restore knee function through precise implant positioning.
• Kinematic alignment (KA) and mechanical alignment (MA) are distinct philosophies for femoral component placement in TKA.
• Differences in alignment techniques may impact prosthetic trochlear parameters and patient outcomes.

Purpose of the Study:

• To compare the trochlear fill and groove orientation of prosthetic components created using KA versus MA techniques.
• To test the hypotheses that MA and KA femoral implants understuff the native trochlear surface and poorly restore native groove orientation.
• To evaluate differences in prosthetic trochlear groove orientation and fill between MA and KA.

Main Methods:

• Three-dimensional femur models were created from MRI scans of patients with medial tibiofemoral osteoarthritis.
• In-house software was used to perform both KA and MA of a cruciate-retaining femoral component.
• Differences in trochlear fit parameters between native and prosthetic trochleae, and between KA and MA, were analyzed.

Main Results:

• MA prosthetic trochleae understuffed the native medial facet and proximal groove/lateral facet, with an 8° more valgus groove orientation compared to native.
• KA prosthetic trochleae understuffed the proximal native trochleae, with a 6° more valgus groove orientation.
• KA resulted in less distal medial facet understuffing and a groove orientation 2° less valgus and 3° more internally rotated than MA.

Conclusions:

• Both MA and KA techniques result in significant understuffing of the native trochlear anatomy and a more valgus prosthetic groove.
• Distinct differences in trochlear fill and groove alignment were observed between MA and KA techniques.
• Future femoral component designs for KA may improve patient satisfaction by better restoring native trochlear anatomy.