Rotational alignment of tibial components in mobile-bearing TKA: posterior substituted vs. PCL retaining

The medial border of the tibial tubercle (MBTT) is one of the fixed anatomic landmarks for tibial component setting during total knee arthroplasty (TKA). In mobile-bearing TKA using a tibial cut first technique, the final tibial component rotation can be guided by the position it achieves following several flexion-extension cycles. In this study, tibial component angle (TCA) and tibial rotational angle (TRA) were determined in dependence of retention or resection of the posterior cruciate ligament (PCL).

The TCA and TRA were examined in 206 patients who underwent primary TKA (PCL retaining: 104 knees, PCL substituting: 102 knees). The tibial component rotation was intraoperatively setting between the parallel to the axis of the most medial aspect of the tibial tubercle as the anterior anatomic landmark and the center of the tibial component as the posterior landmark at the maximum coverage with the osteotomized tibial plateau with its adjustment after several knee flexion-extension exercises. A postoperative quantitative three-dimensional computed tomography technique was used for measurements by a single observer.

The TCA showed a divergence of 0.21° external to the MBTT in the PCL-retaining design and 1.62° internal divergence in the PCL-substituting design. The TRA showed an internal divergence of 0.88° in the PCL-retaining design and an internal divergence of 2.12° in the PCL-substituting design. There were no significant differences between the two designs.

The MBTT might be regarded as a reliable landmark for obtaining an acceptable tibial rotational setting in mobile-bearing TKA despite PCL retention.