ISAKOS: 2019 Congress in Cancun, Mexico
ISAKOS

2019 ISAKOS Biennial Congress ePoster #1513

 

Virtual Reconstruction of the Posterior Cruciate Ligament for Mechanical Testing of the Knee

Julian Joseph Sonnenfeld, MD, Mineola, NY UNITED STATES
Nana Sarpong, MD, MBA, New York, NY UNITED STATES
Sally LiArno, PhD, Mahwah, NJ UNITED STATES
Raga Rajaravivarma , MS, Mahwah, NJ UNITED STATES
Sonia Donde, MS, Mahwah, NJ UNITED STATES
Emily Sneddon, MS, Mahwah, NJ UNITED STATES
Tatyana Kaverina, MS, Mahwah, NJ UNITED STATES
Roshan P. Shah, MD, JD, New York, NY UNITED STATES
Jeffrey A. Geller, MD, New York, NY UNITED STATES

Stryker, Mahwah, NJ, UNITED STATES

FDA Status Not Applicable

Summary

This study indicates that a virtually reconstructed three-fiber model of the PCL simulated with an six-axis hydraulic testing machine can restore kinematics and provide an approach to obtain clinically relevant kinematics when testing total knee replacements under force control.

Abstract

In order to replicate clinically relevant kinematics when testing a total knee replacement (TKR) under force control, it is essential to simulate the restraint obtained from the soft tissues of the knee. Previous work has focused on creating a virtual anterior cruciate ligament, however, a virtual posterior cruciate ligament (PCL) is yet to be elucidated. Therefore, our objective was to determine if virtually reconstructing the PCL in a six-axis hydraulic testing machine could substitute for the absence of the physical ligament.

Three cadaveric knee specimens were dissected such that all soft tissue was removed with the exception of the PCL, ACL, and the collateral ligaments. The knee was mounted in a 6-axis AMTI VIVO (AMTI, Watertown, MA) hydraulic testing machine. The femoral and tibial ligament insertion points were digitized using a Revware Microscribe (Raleigh, NC). Testing was first completed with the intact knee. A posterior drawer test was first completed at 0?, 45 degrees and 90 degrees flexion. Additionally, knee kinematics were measured during simulated stair climbing and deep knee bend for later verification of the virtual soft tissue model during activities of daily living. All tests were then repeated after transection of the PCL. Results from the posterior drawer tests (difference in knee stiffness before and after PCL transection) were used to determine initial parameters for PCL stiffness. The acquired data on the ligament stiffness and the ligament insertion locations were then utilized to construct a virtual soft-tissue model composed of three virtual ligament fibers representing the PCL. One virtual ligament fiber was used to represent the posteromedial (PM) bundle of the PCL and two fibers were used to represent the anterolateral (AL) bundle. The posterior drawer test was then repeated and the PCL parameters (stiffness and insertion points) were optimized until the displacement of the PCL-deficient knee with the virtual PCL bundles approximated that of the intact knee. For verification, the PCL-deficient knee with the virtual PCL was tested under stair-climbing and deep knee bend activities and the resultant kinematics compared to that of the intact knee. A Root Mean Square (RMS) between both sets of kinematics of less than 10% was considered adequate to virtually simulate the PCL.

Ligament stiffness and reference strain was similar among all 3 specimens. The PM bundle represented 2.5 times the stiffness of the AL bundle. Although varying in magnitude, the same trend in kinematics was seen for all 3 specimens, with additional posterior translation occurring following transection of the PCL. The RMS of the difference in kinematics (stair climbing and deep knee bend) between the virtually reconstructed knee and the intact knee was found to be within 6-8% for all tests.

To our knowledge, this study is the first report of implementing a multi-fiber virtual PCL in a hydraulic testing machine. This study indicates that a virtually reconstructed three-fiber model of the PCL can restore kinematics within a goal of 10% RMS. Such an approach is valuable to obtain clinically relevant kinematics when testing total knee replacements under force control.