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Anterior Cruciate Ligament Bundles Elongation Patterns During Fast Running and Single-Leg Drop Landing: An In Vivo
Kohei Kamada1,2, Tom Gale2, Koji Nukuto1,2,3
1Biodynamics Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
Background:
Understanding the anterior cruciate ligament (ACL) anteromedial bundle (AMB) and posterolateral bundle (PLB) elongation patterns during physiologic loading may inform graft-tensioning strategies in double-bundle ACL reconstructions. However, limited evidence exists regarding their in vivo elongation during high-impact activities.
Purpose:
To quantify the relative elongation of AMB and PLB during fast running and single-leg drop landing and to identify the knee flexion angle at peak elongation.
Study Design:
Descriptive laboratory study.
Methods:
Nineteen healthy athletes performed fast running and single-leg drop landing within a biplane radiography system. Tibiofemoral motion was tracked using a validated model-based tracking process that matched computed tomography-based subject-specific 3-dimensional bone models to synchronized biplane radiographs. ACL femoral and tibial attachment points were identified on magnetic resonance imaging and registered to the bone models. AMB and PLB lengths were calculated and normalized to lengths during supine computed tomography to determine relative elongation. Fast running kinematics were analyzed over the first 60% of stance (0% = initial contact, 100% = toe-off). Single-leg drop landing kinematics were analyzed from initial contact (0%) to maximum knee flexion (100%).
Results:
During fast running, AMB peak relative elongation was significantly greater than PLB (mean difference, 2.6%; 95% CI, 1.5-3.6; P < .001). During single-leg drop landing, PLB peak relative elongation was comparable with AMB (mean difference, -0.9%; 95% CI, -2.2% to 0.4%; P = .17). Peak relative elongation occurred at 29° (AMB) and 27° (PLB) of knee flexion during fast running (mean difference, 1.6°; 95% CI, 0.2°-3.0°; P = .029) and at 14° (AMB) and 8° (PLB) of knee flexion during single-leg drop landing (mean difference, 5.9°; 95% CI, 2.5°-9.4°; P < .001).
Conclusion:
AMB elongates more than PLB during fast running, whereas PLB elongates to a similar extent as AMB during single-leg drop landing. Peak elongations occur simultaneously during fast running, while PLB elongates earlier than AMB during single-leg drop landing.
Clinical Relevance:
These findings suggest that fixing AMB at 14° of knee flexion and PLB at a slightly lower angle may better reproduce native bundle function during high-impact activities.
