Introduction

The principle for success in primary total knee arthroplasty is ensuring a well-aligned and balanced construct. The soft tissue aspect of knee replacement is crucial for stability and for optimizing kinematic function. However, knees with large angular deformities are often difficult to correct using established soft tissue techniques and may result in instability and ultimately implant failure. In these situations the use of additional constraint using a conforming polyethylene post might enhance stability.

The use of constrained condylar implants in primary total knee arthroplasty has been previously described. These implant systems have used a conforming polyethylene post that articulates with a femoral component with a matching intercondylar box. The intent of this post-box constraint is to resist not only posterior tibial translation relative to the femur (ie, posterior stabilization) but also to provide resistance to varus/valgus bending moments.

The femoral component in such constrained knee implants was traditionally used with a supplemental femoral rod. There is increasing experience with so-called nonmodular devices that do not use augmented femoral rods. Anderson and colleagues reported excellent results using this system in a series of 61 patients with preoperative valgus alignment; only 1 failure occurred caused by patellar instability. However, little information exists regarding the integrity of the polyethylene post and the articular surface ex vivo. This study evaluated the location and extent of damage of a consecutive series of retrieved nonmodular constrained condylar implants to determine what clinical or radiographic factors may be associated with observed damage modes.