Long term outcome of total knee arthroplasty. Condylar constrained prostheses

Abstract

Constraint is a limitation of motion in a joint, which restricts one or more degrees of freedom in motion either due to an axis mechanism or to a conformity between two articulating surfaces [1]. In total knee arthroplasty (TKA) constraint is defined as the effect of the elements of the implant design which provides the stability needed when static and dynamic knee stabilisers are efficient [2]. The target for a pain free and well-functioning TKA is the achievement of a stable joint based on both adequate balance and function of the ‘extrinsic’ stability provided by the soft tissue envelope and the ‘intrinsic’ stability or constraint provided by the implant design. The balancing of these two elements and the avoidance of so-called kinematic conflict are the most challenging issues for surgical technique in TKA. With contemporary cruciate retaining or posterior stabilized TKAs restoration of normal knee kinematics depends on restoration of normal knee geometry and soft tissue balancing and thus requires as little implant constraint as possible [3]. When these principles cannot be met and the knee remains intra operatively unstable or, during balancing, soft tissue structures fail, a more constrained implant should be used in order to prevent instability, pain and ultimately failure. Although controversy still exists concerning relative indications and the degree of constraint which is introduced in TKA, the use of the least constraint possible is generally advised [4, 5]. Constrained implants are commonly used in complex revision cases but they can also be utilized in difficult primary TKAs.