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Research Papers

Asymmetric Varus and Valgus Stability of the Anatomic Cadaver Knee and the Load Sharing Between Collateral Ligaments and Bearing Surfaces

[+] Author and Article Information
Xiaonan Wang

Physiology, Biophysics,
and Systems Biology Program,
Weill Cornell Graduate School
of Medical Sciences,
Hospital for Special Surgery,
New York, NY 10021

Aamer Malik, Thomas L. Wickiewicz

Department of Orthopaedic Surgery,
Hospital for Special Surgery,
New York, NY 10021

Donald L. Bartel

Department of Biomechanics,
Hospital for Special Surgery,
New York, NY 10021

Timothy Wright

Department of Biomechanics,
Hospital for Special Surgery,
New York, NY 10021
e-mail: wrightt@hss.edu

1Corresponding author.

Manuscript received June 25, 2013; final manuscript received April 20, 2014; accepted manuscript posted May 14, 2014; published online June 3, 2014. Assoc. Editor: Tammy L. Haut Donahue.

J Biomech Eng 136(8), 081005 (Jun 03, 2014) (6 pages) Paper No: BIO-13-1278; doi: 10.1115/1.4027662 History: Received June 25, 2013; Revised April 20, 2014; Accepted May 14, 2014

Knee joint stability is important in maintaining normal joint motion during activities of daily living. Joint instability not only disrupts normal motion but also plays a crucial role in the initiation and progression of osteoarthritis. Our goal was to examine knee joint coronal plane stability under varus or valgus loading and to understand the relative contributions of the mechanisms that act to stabilize the knee in response to varus–valgus moments, namely, load distribution between the medial and lateral condyles and the ligaments. A robot testing system was used to determine joint stability in human cadaveric knees as described by the moment versus angular rotation behavior under varus and valgus loads at extension and at 30 deg and 90 deg of flexion. The anatomic knee joint was more stable in response to valgus than varus moments, and stability decreased with flexion angle. The primary mechanism for providing varus–valgus stability was the redistribution of the contact force on the articular surfaces from both condyles to a single condyle. Stretching of the collateral ligaments provided a secondary stabilizing mechanism after the lift-off of a condyle occurred. Compressive loads applied across the knee joint, such as would occur with the application of muscle forces, enhanced the ability of the articular surface to provide varus–valgus moment, and thus, helped stabilize the joint in the coronal plane. Coupled internal/external rotations and anteroposterior and medial–lateral translations were variable and in the case of the rotations were often as large as the varus–valgus rotations created by the applied moment.

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Figures

Grahic Jump Location
Fig. 1

Robot testing system. (a) Robotic arm and the load cell. (b) Digitizer, and (c) Digitization points and tibial and femoral coordinate systems.

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Fig. 2

(a) Schema of a moment versus angular rotation curve of the intact knee joint describing the initial high stiffness region, intermediate low stiffness region, and final high stiffness region that occurred as the applied moment increased. (b) A typical curve of one of the specimens at full extension.

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Fig. 3

Average angular rotations under 200 N compression and 10 N m varus and valgus moment at 0 deg, 30 deg, and 90 deg of flexion (n = 11)

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Fig. 4.

Average (±standard deviation) of load sharing on the articular surfaces and the ligaments (n = 7) at 10 N m moment with 200 N compression. (a) At 0 deg of flexion; (b) at 30 deg of flexion, and (c) at 90 deg of flexion.

Grahic Jump Location
Fig. 5

(a) Varus and valgus stability of intact cadaver knees with 200 N and 10 N compressive load. The target moments were 10 N m and 6 N m, respectively (n = 7). (b) The averages (±standard deviation) for angular rotation at the 6 N m moment with different compression forces across the joint at full extension (n = 11). (c) Average load sharing at 6 N m moment with 200 N and 10 N compression.

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