The Complex Relationship Between In Vivo ACL Elongation and Knee Kinematics During Walking and Running

Abstract

In vivo anterior cruciate ligament (ACL) bundle (anteromedial bundle [AMB] and posterolateral bundle [PLB]) relative elongation during walking and running remain unknown. In this study, we aimed to investigate in vivo ACL relative elongation over the full gait cycle during walking and running. Ten healthy volunteers walked and ran at a self-selected pace on an instrumented treadmill while biplane radiographs of the knee were acquired at 100 Hz (walking) and 150 Hz (running). Tibiofemoral kinematics were determined using a validated model-based tracking process. The boundaries of ACL insertions were identified using high-resolution magnetic resonance imaging (MRI). The AMB and PLB centroid-to-centroid distances were calculated from the tracked bone motions, and these bundle lengths were normalized to their respective lengths on MRI to calculate relative elongation. Maximum AMB relative elongation during running (6.7 ± 2.1%) was significantly greater than walking (5.0 ± 1.7%, p = 0.043), whereas the maximum PLB relative elongation during running (1.1 ± 2.1%) was significantly smaller than walking (3.4 ± 2.3%, p = 0.014). During running, the maximum AMB relative elongation was significantly greater than the maximum PLB relative elongation (p < 0.001). ACL relative elongations were correlated with tibiofemoral six degree-of-freedom kinematics. The AMB and PLB demonstrate similar elongation patterns but different amounts of relative elongation during walking and running. The complex relationship observed between ACL relative elongation and knee kinematics indicates that ACL relative elongation is impacted by tibiofemoral kinematic parameters in addition to flexion/extension. These findings suggest that ACL strain is region-specific during walking and running. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1920-1928, 2019.

Keywords: anterior cruciate ligament; biplane radiography system; elongation; running; walking.

Figure 1.. Data collection and processing using the biplane radiography system.

Two sets of radiographic generators, image intensifiers and high-speed digital video cameras simultaneously acquired dynamic radiographic images during level walking and running on an instrumented treadmill. Biplane radiographs and subject-specific 3D bone models, obtained from high-resolution computed tomography, were registered using a previously validated model-based tracking process to determine tibiofemoral kinematics.

Figure 2.. Representation of the ACL insertions division into two bundles

(A) Femoral and (B) tibial ACL insertions. The red dots indicate the boundaries of whole ACL insertions, and the blue dots indicate the centroids of the insertions of AM and PL bundles of the right knee. White dotted lines indicate the principle long axis on femur and the projected ACL axis on tibia, respectively. Black lines are the calculated borders of AM and PL bundles. AM: anteromedial, PL: posterolateral

Figure 3.. ACL relative elongation during walking and running.

The blue and pink lines indicate the mean AMB and PLB relative elongation, respectively, for the entire group of participants. Shaded area indicates 95% confidence interval. AMB: anteromedial bundle, PLB: posterolateral bundle

Figure 4.. The complex relationship between the ACL bundle elongation and knee flexion angle during walking.

Scatter plots of the average data of (A) AMB and (B) PLB elongation versus knee flexion angle during walking. (C) The average data of knee flexion angle over the full gait cycle during walking. The four colored dots indicate key gait cycle instants. The numbers and arrows correspond to gait phases between key instants of the gait cycle.

Figure 5.. The complex relationship between ACL bundle elongation and knee flexion angle during running

Scatter plots of the average data of (A) AMB and (B) PLB elongation versus knee flexion angle during running. (C) The average data of knee flexion angle over the full gait cycle during running. The four colored dots indicate key gait cycle instants. The numbers and arrows correspond to gait phases between key instants of the gait cycle.