Removal or retention—will we ever know? The posterior cruciate ligament in total knee replacement

For more than 2 decades the question regarding retention or removal of the posterior cruciate ligament during total knee arthroplasty has appeared at congresses, instructional courses and in orthopedic journals. One reason for this intense debate is that the scientific evidence behind choice of surgical technique—and its consequences—is limited, as reported in a meta-analysis by Jacobs et al. (2005) in this issue of Acta Orthopaedica (pages 757–768).

Little is known about the detailed weight-bearing kinematics of the knee after posterior cruciate ligament rupture in the natural knee also. Even though this topic has been studied using both MRI and radiostereometry, these studies were not dynamic and the existence of any associated injuries was not completely known (Jonsson and Kärrholm 1999, Logan et al. 2004). According to Logan et al. (2004), the medial femoral condyle will more or less always adopt an anteriorly displaced position, whereas the motion and position of the lateral condyle and rotations of the knee seem to be unaffected.

Our limited knowledge about the importance of the PCL for normal knee kinematics and function may explain the lack of consensus regarding the optimum treatment of the PCL in total knee arthroplasty. This may have been the reason for the divergent designs of the early TKRs, either intended to spare both the anterior and the posterior cruciate ligament (e.g. the Geomedic), or as for the cruciate removing designs such as the Freeman-Samuelsson and the Total Condylar prosthesis, to substitute for these ligaments by increased inherent stability (Freeman and Railton 1988). Later on, posterior cruciate substitution with a central tibial post and a corresponding box on the femoral component was introduced, often as a design option to an existing standard prosthesis.