The relationship between anteroposterior stability and medial–lateral stability of the bi-cruciate stabilized total knee arthroplasty

Acquisition of appropriate anteroposterior (AP) stability depends on the prosthetic design and intraoperative soft tissue handling. A bi-cruciate stabilized (BCS) total knee arthroplasty (TKA) has a two cam-post mechanism, which substitutes for the anterior cruciate ligament and posterior cruciate ligament (PCL). Therefore, appropriate AP stability is expected. Because the PCL is sacrificed during BCS TKA, medial stability and lateral stability are thought to be important factors to determine AP stability. However, no previous study has reported AP stability after BCS TKA and the relationship between AP and medial–lateral stability.

AP stability was measured using a navigation system intraoperatively and the KT 2000 device postoperatively. Intraoperative joint laxity of the medial and lateral compartments was evaluated separately using a compartment-specific ligament tensioner. The relationship between AP stability and medial–lateral laxity was assessed.

Intraoperative AP translation at 30° and 90° knee flexion angles was 7.7 ± 3.1 mm and 5.9 ± 2.0 mm, respectively. Postoperative AP translation at 30° was 5.9 ± 1.7 mm. AP translation correlated positively with medial joint laxity at 30° (R = 0.29) and 90° (R = 0.40). The intraoperative and postoperative AP translations at 30° flexion had a positive relationship (R = 0.61).

AP stability of the BCS TKA had a positive relationship with intraoperative medial stability. Therefore, surgical soft tissue handling focusing on medial stability is also appropriate for AP stability of BCS TKA. Additionally, intraoperative AP translation turned out to be a predictive indicator for postoperative knee AP stability at 30° flexion.