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TECHNICAL PAPERS: Joint/Whole Body

Effect of ACL Deficiency on MCL Strains and Joint Kinematics

[+] Author and Article Information
Trevor J. Lujan, Michelle S. Dalton, Brent M. Thompson, Benjamin J. Ellis

Department of Bioengineering, University of Utah, Salt Lake City, UT 84112

Jeffrey A. Weiss1

Department of Bioengineering, University of Utah, Salt Lake City, UT 84112jeff.weiss@utah.edu

1

Corresponding author.

J Biomech Eng 129(3), 386-392 (Nov 06, 2006) (7 pages) doi:10.1115/1.2720915 History: Received May 12, 2006; Revised November 06, 2006

The knee joint is partially stabilized by the interaction of multiple ligament structures. This study tested the interdependent functions of the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) by evaluating the effects of ACL deficiency on local MCL strain while simultaneously measuring joint kinematics under specific loading scenarios. A structural testing machine applied anterior translation and valgus rotation (limits 100N and 10Nm, respectively) to the tibia of ten human cadaveric knees with the ACL intact or severed. A three-dimensional motion analysis system measured joint kinematics and MCL tissue strain in 18 regions of the superficial MCL. ACL deficiency significantly increased MCL strains by 1.8% (p<0.05) during anterior translation, bringing ligament fibers to strain levels characteristic of microtrauma. In contrast, ACL transection had no effect on MCL strains during valgus rotation (increase of only 0.1%). Therefore, isolated valgus rotation in the ACL-deficient knee was nondetrimental to the MCL. The ACL was also found to promote internal tibial rotation during anterior translation, which in turn decreased strains near the femoral insertion of the MCL. These data advance the basic structure-function understanding of the MCL, and may benefit the treatment of ACL injuries by improving the knowledge of ACL function and clarifying motions that are potentially harmful to secondary stabilizers.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Twenty-one markers defined 18 regions for strain measurement. The markers in rows 1 and 2 were affixed to the anterior and posterior longitudinal fibers of the superficial MCL. Markers in row 3 inferior to the joint line were considered affixed to the distal oblique fibers of the superficial MCL. Markers in row 3 superior to the joint line were considered affixed to the anterior posteromedial corner.

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Figure 5

MCL strain changes due to ACL transection at peak anterior translation and valgus rotation, averaged over all cases. Transection significantly increased MCL strains during anterior translation, but had no effect on MCL strains during valgus rotation. * p<0.05 (within a region).

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Figure 6

(A) Internal tibial axial rotation from neutral to peak anterior translation, 30deg knee flexion, before and after ACL transection. (B) Average MCL strains at peak anterior translation, 30deg knee flexion, with fixed and unconstrained tibial axial rotation, before and after ACL transection. In the ACL-intact knee, unconstraining tibia axial rotation significantly reduced strain along the anterior MCL. After ACL transection, internal tibial rotation was significantly decreased and MCL strain was unaffected when tibial axial rotation was unconstrained. Thus, in the intact knee, the ACL promoted internal tibial rotation during anterior translation, which relieved strain in the MCL. This also occurred at 60deg and 90deg flexion. * p<0.05.

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Figure 2

Schematic of the loading apparatus, depicting a medial view of the knee at 0deg flexion. Kinematic blocks are rigidly attached to the tibia and femur for 3D motion measurement. (A) Applied anterior-posterior tibial translation. (B) Applied varus-valgus rotation. (C) Adjustable flexion angle. (D) Constrained or unconstrained tibial axial rotation. (E) Unconstrained medial-lateral translation and joint distraction. (F) Load/torque cell.

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Figure 3

(A) Anterior tibial displacements at all flexion angles, with unconstrained tibial axial rotation, before and after ACL transection. (B) Average MCL strains at peak anterior translation as a function of flexion angle, with unconstrained tibial axial rotation, before and after ACL transection. Knee anterior laxity and MCL strains significantly increased at each flexion angle in the ACL-deficient knee. * p<0.05, error bars=SD.

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Figure 4

(A) Valgus rotation at all flexion angles, with unconstrained tibial axial rotation, before and after ACL transection. (B) Average MCL strains at peak valgus rotation as a function of knee flexion angle, with unconstrained tibial axial rotation, before and after ACL transection. ACL transection had no significant effect on valgus laxity or MCL strains. Error bars=SD.

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