Summary

Intraoperative varus-valgus joint laxity patterns throughout a knee range of motion after bicruciate-stabilized total knee replacement, which were assessed using a navigation system, were associated with knee flexion angles and patient-reported outcomes (Knee injury and Osteoarthritis Outcome Score and the patient satisfaction score in the 2011 Knee Society Score) at one year postoperatively.

Abstract

Background

In recent-introduced robot-assisted total knee arthroplasties (TKAs) including bicruciate-stabilized (BCS) TKA, the mediolateral laxity under a varus-valgus force is used to determine the amount of bone resection and implant placement angle. However, the evidence regarding what laxity patterns should be aimed for to achieve better postoperative outcomes is still insufficient. This study aimed to clarify the relationship between the pattern of intraoperative varus-valgus laxity throughout a knee range of motion (ROM) after implant placement and postoperative clinical outcomes in BCSTKA.

Methods

One hundred and thirty-four patients [28 males and 106 females with a mean age of 72 years and a mean body mass index (BMI) of 24.7 kg/m2] who underwent mechanical axis aligned primary BCSTKA using an image-free computer navigation for primary varus osteoarthritis were included. After the final implantation and capsule closure, joint laxity (JL) under a maximum varus–valgus stress was recorded with navigation. The amount of change in varus and valgus angles from the unstressed mechanical axis were defined as the lateral and medial JL under a varus-valgus force (JLVV) respectively. The patients were categorized into three groups [Pattern (P) 1–3; P1, n=47; P2, n=55; P3, n=32] based on the medial and lateral JLVVs at a knee flexion of 10°, 30°, 60°, 90° and 120° using hierarchical cluster analysis. The JLVV patterns, the patients’ characteristics (age, gender, BMI and preoperative HKA), and the pre- and postoperative one-year ROM and patient-reported outcome measures (PROMs) [Knee injury and Osteoarthritis Outcome Score (KOOS) and the 2011 Knee Society Score (KSS) satisfaction score] were compared among the three clusters.

Results

There were no significant differences in patient background, preoperative ROM, KOOS and 2011 KSS satisfaction score among the three clusters.
Regarding JLVV patterns, P1 showed medial JLVV of 3° or more at knee flexion of 30°, 60° and 120°, all of which were significantly larger than P2 and P3 (p <0.01). The medial JLVVs in P2 were less than 3 degrees throughout the knee ROM without significant change, whereas the medial JLVV at 120° in P3 were smaller than the medial JLVV at 90° (p =0.02). On the other hand, the lateral JLVV in all clusters increased with knee flexion. In each cluster, the lateral JLVV showed the maximum value at 90° of knee flexion, and the values were 4° in P1, 6° in P2 and 10° in P3.
Regarding the postoperative one-year ROM, P2 and P3 had significantly better flexion angles than P1 (P1, 120°; P2, 128°; P3, 129°; p <0.01). Moreover, one-year postoperative KOOS symptom score (P1, 80; P2, 86; p =0.03) and the 2011 KSS satisfaction score (P1, 26; P2, 30; p <0.01) in P2 were better than those of P1.

Discussion

Patients with the stable medial JLVV less than 3° throughout entire knee ROM combined with the lateral JLVV of approximately 6° achieved better postoperative knee flexion angle and PROMs at postoperative one year in BCSTKA.

Conclusion

Intraoperative JLVV pattern throughout a knee ROM was associated with postoperative knee flexion angle and PROMs in BCSTKA.