The Cruciate Ligaments in Total Knee Arthroplasty
The early knee replacements were hinge designs that ignored the ligaments of the knee and resurfaced the joint, allowing freedom of motion in a single plane. Advances in implant fixation paved the way for modern designs, including the posterior-stabilized (PS) total knee arthroplasty (TKA) that sacrifices both cruciate ligaments while substituting for the posterior cruciate ligament (PCL), and the cruciate-retaining (CR) TKA designs that sacrifice the anterior cruciate ligament but retain the PCL. The early bicruciate retaining (BCR) TKA designs suffered from loosening and early failures. Townley and Cartier designed BCR knees that had better clinical results but the surgical techniques were challenging.
Kinematic studies suggest that normal motion relies on preservation of both cruciate ligaments. Unicompartmental knee arthroplasty retains all knee ligaments and closely matches normal motion, while PS and CR TKA deviate further from normal. The 15% to 20% dissatisfaction rate with current TKA has renewed interest in the BCR design. Replication of normal knee kinematics and proprioception may address some of the dissatisfaction.
However, only 80% to 90% of patients are fully satisfied with their implants. The reasons for the dissatisfaction include unexplained anterior knee pain, stiffness, unexplained swelling, loss of range of motion, changes in proprioception, and loss of preoperative functions.14
The mid-term results of the BCR knees that were performed in the 1980s showed similar results to the CR and PS knees. Townley8 reported excellent clinical results with only 2% loosening at 2 to 11 years after surgery. Cloutier and colleagues9 reported 95% survival with improved proprioception at 9 to 11 years after surgery(Table 2).62,63
Studies comparing traditional TKA designs with cruciate preserving designs, both UKA and BCR, have found differences in subjective outcomes.62,64 Comparison of UKA and TKA in the same patient demonstrated significant preference for UKA, particularly with stair-climbing.65 Similarly, comparison between BCR and PS TKA or CR TKA demonstrated preference for BCR in 85% of patients.62
The new BCR knee designs have just started to come to the market.50 The surgical techniques are much improved over the 1980s and cruciate preservation is certainly much easier now. The new designs can produce full range of motion with kinematics that are almost identical to the normal knee in the cadaver laboratory and in computer analyses. These designs certainly should have a similar 20-year survival to the original BCR knees. However, the critical evaluation will be the patient satisfaction scores. With greater motion, better kinematics, and more precise balancing the scores would improve with these designs.
Conclusion
The cruciate ligaments of the knee are central to control of the motion of the normal knee. TKA is a successful operation with at least a 40- to 50-year history. The techniques have continued to develop but 15% to 20% of patients are dissatisfied with the results.14 Evaluations of the prostheses are more sophisticated and kinematics appears to have a central position in the evaluation. If the knee is to move more anatomically correctly, all of the ligaments must be preserved. Proprioception certainly plays a role in the patient’s judgment of the result. History has shown that a BCR knee can be implanted with good mid-term results and it should certainly be possible to build on these results and design a knee that will incorporate all of the ligaments with full range of motion and increased levels of activity.
