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Research Papers

A Combined Experimental and Computational Approach to Subject-Specific Analysis of Knee Joint Laxity

[+] Author and Article Information
Michael D. Harris

Department of Mechanical
and Materials Engineering,
University of Denver,
2390 S York Street,
Denver, CO 80208
e-mail: michael.d.harris@hotmail.com

Adam J. Cyr

Department of Mechanical
and Materials Engineering,
University of Denver,
2390 S York Street,
Denver, CO 80208;
Department of Mechanical Engineering,
University of Kansas,
3138 Learned Hall,
Lawrence, KS 66045
e-mail: adamjcyrphd@gmail.com

Azhar A. Ali

Department of Mechanical
and Materials Engineering,
University of Denver,
2390 S York Street,
Denver, CO 80208
e-mail: azhar.ali@du.edu

Clare K. Fitzpatrick

Department of Mechanical
and Materials Engineering,
University of Denver,
2390 S York Street,
Denver, CO 80208
e-mail: clare.fitzpatrick@du.edu

Paul J. Rullkoetter

Department of Mechanical
and Materials Engineering,
University of Denver,
2390 S York Street,
Denver, CO 80208
e-mail: paul.rullkoetter@du.edu

Lorin P. Maletsky

Department of Mechanical Engineering,
University of Kansas,
3116 Learned Hall,
Lawrence, KS 66045
e-mail: maletsky@ku.edu

Kevin B. Shelburne

Department of Mechanical
and Materials Engineering,
University of Denver,
2390 S York Street,
Denver, CO 80208
e-mail: kevin.shelburne@du.edu

1Corresponding author.

Manuscript received September 17, 2015; final manuscript received June 3, 2016; published online June 29, 2016. Assoc. Editor: Tammy L. Haut Donahue.

J Biomech Eng 138(8), 081004 (Jun 29, 2016) (8 pages) Paper No: BIO-15-1462; doi: 10.1115/1.4033882 History: Received September 17, 2015; Revised June 03, 2016

Modeling complex knee biomechanics is a continual challenge, which has resulted in many models of varying levels of quality, complexity, and validation. Beyond modeling healthy knees, accurately mimicking pathologic knee mechanics, such as after cruciate rupture or meniscectomy, is difficult. Experimental tests of knee laxity can provide important information about ligament engagement and overall contributions to knee stability for development of subject-specific models to accurately simulate knee motion and loading. Our objective was to provide combined experimental tests and finite-element (FE) models of natural knee laxity that are subject-specific, have one-to-one experiment to model calibration, simulate ligament engagement in agreement with literature, and are adaptable for a variety of biomechanical investigations (e.g., cartilage contact, ligament strain, in vivo kinematics). Calibration involved perturbing ligament stiffness, initial ligament strain, and attachment location until model-predicted kinematics and ligament engagement matched experimental reports. Errors between model-predicted and experimental kinematics averaged <2 deg during varus–valgus (VV) rotations, <6 deg during internal–external (IE) rotations, and <3 mm of translation during anterior–posterior (AP) displacements. Engagement of the individual ligaments agreed with literature descriptions. These results demonstrate the ability of our constraint models to be customized for multiple individuals and simultaneously call attention to the need to verify that ligament engagement is in good general agreement with literature. To facilitate further investigations of subject-specific or population based knee joint biomechanics, data collected during the experimental and modeling phases of this study are available for download by the research community.

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References

Figures

Grahic Jump Location
Fig. 1

Experimental setup for laxity testing. Each leg was inverted, with the femur rigidly mounted to a base and a 6DOF load cell attached to the distal tibia. Optotrak arrays tracked segment motion while torques and displacements were manually applied.

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Fig. 2

Medial (left) and lateral (right) views of FE model from one knee. Yellow dots indicate digitized points taken during the experiments to identify attachment locations for the LCL, MCL, ACL, and PCL. Other ligaments were placed based on anatomical descriptions.

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Fig. 3

Experimental and FE model torque versus displacement curves at 30 deg flexion for the resected (top) and intact (bottom) cases. Positive torque or force values and positively directed rotation and displacement values represent valgus, external, and anterior.

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Fig. 4

Engagement of ligaments contributing to resistance of tibia motion during (a) varus, (b) valgus, (c) internal, (d) external, (e) anterior, and (f) posterior tests for the intact state. Forces represented are the average and standard deviation forces for all knees at the end of the applied 10 N·m for VV or 8 N·m for IE torque tests. For AP tests, not all knees reached 80 N during experimental testing; shown here are averages at applied forces of 50 N for anterior and 80 N for posterior.

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Fig. 5

Representation of force within ligaments engaged during external rotation at 0 deg flexion (left) compared to 45 deg flexion (right). Arrow sizes indicate ligament forces in the four. Major contributors during external rotation were the PFL and MCL. The MCLA of knee 04, particularly, became increasingly engaged as flexion increased.

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