Location of the ankle center for total knee arthroplasty

The purpose of this study was to investigate the ankle center position as determined from the malleoli for total knee arthroplasty (TKA).

We retrospectively analyzed computed tomography data from 102 patients with osteoarthritic knees. The tibial anteroposterior (AP) axis and transmalleolar axis (TMA) were used as rotational reference axes of the knee and ankle joint, respectively. With these axes, we regarded the offset distance from the intermalleolar midpoint as the position of the ankle center and investigated any angular osteotomy errors on the proximal tibia when the ankle center was assumed to the intermalleolar midpoint.

The mean offset distances relative to the tibial AP axis were 1.8±0.9mm medial and 4.2±1.2mm anterior, and the distances relative to the TMA were 3.0±0.9 and 3.6±1.1mm in the coronal and sagittal planes, respectively. Mean angular osteotomy errors were 0.3±0.2° in the coronal plane and 0.8±0.2° in the sagittal plane.

The ankle center was located around the intermalleolar midpoint. The position of the ankle center observed along the knee reference axis further approached the intermalleolar midpoint than when observed along the ankle reference axis in the coronal plane, but not in the sagittal plane. And the coronal angular osteotomy error was smaller than the sagittal error. Therefore, the intermalleolar midpoint in the coronal plane is a reliable landmark for the ankle center during TKA. However, surgeons should be cognizant of this sagittal angular error.