The effect of femoral component malrotation on patellar biomechanics.

Oliver Kessler
Oliver Kessler
University of Zurich
Shantanu Patil
Shantanu Patil
Shiley Center for Orthopaedic Research and Education at Scripps Clinic
Clifford W Colwell
Clifford W Colwell
Shiley Center for Orthopaedic Research and Education at Scripps Clinic
United States

J Biomech 2008 Dec 18;41(16):3332-9. Epub 2008 Nov 18.

Scientific Affairs, Stryker Europe, Thalwil, Switzerland.

Patellofemoral complications are among the important reasons for revision knee arthroplasty. Femoral component malposition has been implicated in patellofemoral maltracking, which is associated with anterior knee pain, subluxation, fracture, wear, and aseptic loosening. Rotating-platform mobile bearings compensate for malrotation between the tibial and femoral components and may, therefore, reduce any associated patellofemoral maltracking. To test this hypothesis, we developed a dynamic model of quadriceps-driven open-kinetic-chain extension in a knee implanted with arthroplasty components. The model was validated using tibiofemoral and patellofemoral kinematics and forces measured in cadaver knees. Knee kinematics and patellofemoral forces were measured after simulating malrotation (+/-3 degrees ) of the femoral component. Rotational alignment of the femoral component affected tibial rotation near full extension and tibial adduction at higher flexion angles. External rotation of the femoral component increased patellofemoral lateral tilt, lateral shift, and lateral shear forces. Up to 21 degrees of bearing rotation relative to the tibia was noted in the rotating-bearing condition. However, the rotating bearing had minimal effect in reducing the patellofemoral maltracking or shear induced by femoral component rotation. The rotating platform does not appear to be forgiving of malalignment of the extensor mechanism resulting from femoral component malrotation. These results support the value of improving existing methodologies for accurate femoral component alignment in total knee arthroplasty.

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December 2008
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