Effect of component alignment and ligament balancing on the passive stability of the replaced knee

Abstract

Initial stability of the knee joint is essential if long-term survivorship is to be achieved. At the time of operation the surgeon can assess the stability of the joint by carrying out simple passive stability tests, assessing the integrity of the joint and the laxity of the ligaments. A fully mechanical model of a replaced knee has been developed to simulate this passive stability testing, which is capable of altering parameters such as component positioning and ligament tensions simply and accurately. Internal/external rotational stability of a posterior cruciate-retaining rotating platform knee was assessed under a variety of different knee conditions. Increasing the strains equally in both collateral ligaments increased the axial stability of the knee, with lax ligaments causing the stability to decrease. Varus or valgus malrotation of the femoral component did not significantly affect the femoral rotations of the knee, however the interaction between the femoral and tibial components was significantly altered. A lax medial collateral ligament combined with valgus malrotation of the femoral component caused pivoting to occur on the lateral side of the knee, producing zero internal rotation. This indicates that 100% of the load passes through the lateral side of the knee. The opposite was seen in the varus knee with a slack lateral collateral ligament.

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ORCID for Martin Browne: orcid.org/0000-0001-5184-050X

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