Both Intraoperative Medial and Lateral Soft Tissue Balances Influence Intraoperative Rotational Knee Kinematics in Bi-Cruciate Stabilized Total Knee Arthroplasty: A Retrospective Investigation.

Background: Tibial internal rotation following total knee arthroplasty (TKA) is important in achieving favorable postoperative clinical outcomes. Studies have reported the effect of intraoperative soft tissue balance on tibial internal rotation in conventional TKA, however, its effect on bi-cruciate stabilized (BCS) TKA has not reported enough. Furthermore, although studies have shown that both medial and lateral soft tissue balances are important for a good tibial internal rotation, no studies have evaluated the effects of soft tissue balance at medial or lateral compartments separately on tibial internal rotation in BCS TKA. The purpose of this study was to clarify the relationship between medial or lateral component gaps and rotational knee kinematics in BCS TKA. Methods: One hundred fifty-eight knees that underwent BCS TKA were included in this study. They were divided into two groups according to the medial or lateral joint laxities, which was defined as the value of component gap minus the selected thickness of the tibial component at 30°, 60°, and 90° flexion, respectively: Group M-stable (medial joint laxity, ≤2 mm) or Group M-loose (medial joint laxity, ≥3 mm) and Group L-stable (lateral joint laxity, ≤3 mm) or Group L-loose (lateral joint laxity, ≥4 mm). The intraoperative rotational knee kinematics was compared between Group M-stable and Group M-loose or between Group L-stable and Group L-loose at each angle, respectively. Results: The rotational angular difference between 30° flexion and maximum flexion was significantly larger in Group M-stable at 30° flexion than that in Group M-loose at 30° flexion. The rotational angular difference between 60° flexion and maximum flexion was significantly larger in Group L-loose at 60° flexion than that in Group L-stable at 60° flexion. The rotational angular difference between 60° flexion and maximum flexion was significantly larger in Group L-loose at 90° flexion than that in Group L-stable at 90° flexion. Conclusion: Surgeons should pay attention to the importance of medial joint stability at midflexion and lateral joint laxities at midflexion and 90° flexion on a good tibial internal rotation from midflexion to deep flexion in BCS TKA.