Abstract
Background
While posterior cruciate retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bi-cruciate retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. Various fluoroscopic studies have focused on determination of kinematics but haven't defined differentiators that affect motion patterns. This research study assesses the importance of the cruciate ligaments and femoral geometry for Bi-Cruciate Retaining (BCR) and Posterior Cruciate Retaining (PCR) TKAs having the same femoral component, compared to the normal knee.
Methods
The in vivo 3D kinematics were determined for 40 subjects having a PCR TKA, 10 having a BCR TKA, and 10 having a normal knee, in a retrospective study. All TKA subjects had the same femoral component. All subjects performed a deep knee bend under fluoroscopic surveillance. The kinematics were determined during early flexion (ACL dominant), mid flexion (ACL/PCL transition) and deep flexion (PCL dominant).
Results
During the first 30 degrees of flexion, the ACL played an important role, as subjects having a BCR TKA experienced kinematic patterns more similar to the normal knee. During mid flexion, both TKAs experienced random kinematic patterns, which could be due to the ACL and PCL being less active or resected in PCR TKA. In deeper flexion, both TKAs experienced kinematic patterns similar to the normal knee, thus supporting the assumption that the PCL played a dominant role [Fig. 1, Fig. 2]. All three groups generally experienced progressive axial rotation throughout flexion [Fig. 3]. On average, subjects having a PCR TKA experienced 112.3° of flexion, which was greater than the BCR subjects.
Conclusions
Both the BCR TKA and normal groups experienced similar kinematic patterns, but the femoral geometrical differences from the anatomical condition may have influenced decreased motion compared to the normal knee. Both TKAs experienced similar kinematic patterns in deeper flexion, with the PCR TKA experiencing excellent weight-bearing flexion. Results from this study suggest that the cruciate ligaments can play a role in kinematics, but femoral geometry working with the ligaments may be an option to consider.
