Summary

In this study, nonlinear virtual ligaments on knee joints were developed to mimic the natural behavior of knee joints in clinical laxity tests and high-demand activities.

Abstract

Introduction

A thorough understanding of the biomechanical impact of a variety of factors on knee kinematics following anterior cruciate ligament reconstruction (ACLR) is essential for developing surgical procedures to restore knee function. It is still unclear whether the anterolateral complex (ALC) plays a significant role in ACLR knee stability or if it is only significant when the ACL is injured. In this study, we designed specimen-specific virtual ACLR and used that to simulate real ACLR knee behavior that can be added or removed to simulate intact or injured knees. Additionally, the study assessed the effect of ALC lesion on knee stability with both real and virtual ACLR.

Method

Twelve ACLR knees were mounted to a motion simulator. Each was subjected to tests of clinical laxity exams (Pivot-shift, Lachman, and Anterior drawer test) as well as high-demand activities, including cutting maneuver, and inside and outside pivoting. The forces transmitted through ACLR graft were measured using a sequential resection technique. By tuning the measured ligament forces and elongations to a generic non-linear elastic ligament model, virtual ACLR was designed. Virtual ligaments were applied to the knee after removing the ACLR graft and the same motions were applied. Following biomechanical testing of the ACLR and virtual ACLR joints, ALC was dissected by releasing the tibial attachment of the anterolateral ligament from the lateral meniscus and the femoral attachment from the most posterior limit of the iliotibial band leaving the distal Kaplan fibre attachment intact. Using a load cell attached to the ACLR graft, the original ACLR was reinstalled with extra caution to ensure that it was the same ACLR as when the ALC was intact. Then the effect of ALC lesion was measured on both real and then virtual ACLR.

Results

The average difference between the anterior displacement of the tibia with native ACLR versus virtual ACLR was 1.1 mm during Pivot-shift, 2.8 mm during Lachman, and 1.9 mm during the anterior drawer test. The results obtained using both methods did not differ statistically significant. During Pivot-shift, Lachman, and anterior drawer tests the anterior translation of the tibia increased after cutting ALC in real ACLR by 2.3 mm, 1.7 mm, and 1.5 mm, and in virtual ACLR by 1.7 mm, 0.9 mm, and 1.0 mm, respectively. In real and virtual ACLR, there was a statistically significant difference between intact and injured ALC results. The root mean square error (RMSE) between anterior-posterior displacement in real and virtual ACLR was 0.2 mm for cutting maneuvers, and 0.6 mm and 0.9 mm for inside and outside pivoting, respectively, with no statistically significant difference. The dissection of the ALC increased the average of the anterior translation by 0.7 mm, 0.7 mm, and 0.6 mm in the real ACLR and by 0.5 mm, 0.5 mm, and 0.4 mm in the virtual ACLR during the cutting maneuver and inside and outside pivoting, respectively.

Conclusion

In conclusion, a virtual ACLR knee can simulate real ACLR knee behavior and can be used to parametrically analyze joint behavior in the absence or presence of other injuries.