Rotational position of ligament balancer affects medial and lateral soft tissue balance in total knee arthroplasty

Abstract

PurposeThe purpose of this study was to clarify the effect on medial and lateral soft tissue balance for different rotational positions of the balancer. MethodsA total of 65 patients who were operated using a rotational mobile bearing total knee arthroplasty (TKA) have been evaluated. A new balancer was made so that the insert trial could be rotated on the paddle. We measured the angle of deviation to varus or valgus and the rotational angle of the insert trial at Akagi's line (group 0), at 20° of internal rotation from the Akagi's line (group IR), and at 20° of external rotation from the Akagi's line (group ER). ResultsThe IR group had a significantly medial tightness than the other two groups. The ER group had a significantly lateral tightness than the other two groups. All cases were divided into three groups by the position of the insert (neutral, internal rotation and external rotation) on the balancer with respect to Akagi's line after range of motion (ROM) technique. In extension, a significant negative correlation was found between mean varus/valgus balance and rotation of the insert. ConclusionIn mobile bearing TKA, it is possible to obtain the optimal medial and lateral soft tissue balance if the misalignment is within the possible range of rotation allowed by the design of the insert. Anatomical landmarks should also be referenced when determining tibial rotational alignment using the ROM technique, as it was easily influenced by medial and lateral soft tissue balance.