Video Gallery

Video Gallery

To View the Video

Rationale and Reliability of Setting I/E Component Rotation and Restoring Function in Kinematically Aligned TKA

March 15, 2015

Contributors: Alexander J. Nedopil, MD; Maury L Hull, PhD; Stephen M Howell, MD; Stephen M Howell, MD

INTRODUCTION: This video concerning total knee arthroplasty (TKA): 1) provides a rationale for setting internal/external (I/E) rotation of the femoral and tibial components parallel to the sagittal kinematic plane of the knee, 2) shows two methods for setting the A/P axis of the femoral and tibial components parallel to the sagittal kinematic plane, and 3) presents a reliability study that shows the range of I/E rotation of each component from the sagittal kinematic plane and function after kinematically aligned (KA) TKA.

DISCUSSION: The rationale for setting the I/E rotation of the femoral and tibial components parallel to the sagittal kinematic plane is based on the concept of restoring the three kinematic axes of the knee. The natural flexion and extension of the tibia and patella are in the sagittal kinematic plane (Gu, JBJS, 2014). Because an important objective of TKA should be to restore the normal kinematics of the joint and maintain normal ligament length (Kurosawa, J Biomech, 1985), the A/P axes of the femoral and tibial components should be set parallel to the sagittal kinematic plane. The method for setting the I/E rotation of the femoral component is to restore the natural angle and level of the posterior joint line. Wear of femoral bone is rare in Kellgren-Lawrence Grade 3-4 osteoarthritic (OA) knees, and cartilage wear at 90 degrees on the posterior femoral condyle rarely exceeds 1 mm (Nam, KSSTA, 2014). Therefore, resection of the posterior femoral condyles equal in thickness to the posterior condyle of the femoral component (-1mm for kerf) sets the I/E rotation of the femoral condyle in KA TKA (Howell, KSSTA, 2013). The method for setting the I/E rotation of the tibial component is to align the A/P axis of the tibial component parallel to the A/P axis of the nearly elliptical shape of the lateral tibial condyle (Nedopil, Orthop, 2013). The lateral tibial condyle is used to construct the tibial reference line instead of the tibial tubercle because the medial to lateral location of the tibial tubercle varies 15 mm in normal knees, which causes a 40 degree range of I/E rotational error from the sagittal kinematic plane (Howell, KSSTA, 2012).

RESULTS: A study of 71 consecutive patients treated with KA TKA measured the rotation of the femoral and tibial components from the sagittal kinematic plane using synchronized preoperative MRI and postoperative CT scans and measured function (Oxford knee score) at six months. The 0 ± 3 degrees range of femoral component rotation and 0 ± 12 degrees range of tibial component rotation from the sagittal kinematic plane resulted in a high mean Oxford Knee Score of 42 (48 best).

Results for "Primary Knee Arthroplasty"

2 of 4
2 of 4

X