Posterior Stabilized

Abstract

By the mid-1970s, the Total Condylar knee was one the most successful knees on the market in usage and performance. However there were two limitations: the range of flexion averaged only about 90 degrees, and there were cases of flexion instability due to loose collateral ligaments. At the Hospital for Special Surgery, where the Total Condylar originated, it was decided that a modification to the design was needed to solve the two problems. There were already several mechanical features in existing designs to suggest a possible configuration, including the Deane and Attenborough knees from England and the Kinematic Stabilizer from Boston. Insall and Burstein designed the posterior stabilized (PS) design, which had similar bearing surfaces to the Total Condylar but which had an intercondylar cam-post mechanism which operated after mid-flexion to cause rollback of the femur on the tibia. This design solved the limitations of the Total Condylar and started a new design type which became the most widely used of any other design. Today, the PS and a posterior cruciate retaining design type the CR are still the most widely used of any type of artificial knee. Recently, the Ultracongruent knee, essentially a Total Condylar type with more conforming bearing surfaces, is gaining some popularity due to providing the same control of anterior-posterior motion as the PS, but in a simpler design with less bone resection.