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Design Innovation

Design of a Free-Floating Polycarbonate-Urethane Meniscal Implant Using Finite Element Modeling and Experimental Validation

[+] Author and Article Information
Jonathan J. Elsner, Sigal Portnoy, Gal Zur, Avi Shterling

Research and Development Center, Active Implants Corporation, Netanya 42505, Israel

Farshid Guilak

 Duke University Medical Center, Durham, NC 27710

Eran Linder-Ganz1

Research and Development Center, Active Implants Corporation, Netanya 42505, Israeleran.ganz@activeimplants.com

1

Corresponding author.

J Biomech Eng 132(9), 095001 (Aug 17, 2010) (8 pages) doi:10.1115/1.4001892 History: Received April 21, 2010; Revised May 24, 2010; Posted May 31, 2010; Published August 17, 2010; Online August 17, 2010

The development of a synthetic meniscal implant that does not require surgical attachment but still provides the biomechanical function necessary for joint preservation would have important advantages. We present a computational-experimental approach for the design optimization of a free-floating polycarbonate-urethane (PCU) meniscal implant. Validated 3D finite element (FE) models of the knee and PCU-based implant were analyzed under physiological loads. The model was validated by comparing calculated pressures, determined from FE analysis to tibial plateau contact pressures measured in a cadaveric knee in vitro. Several models of the implant, some including embedded reinforcement fibers, were tested. An optimal implant configuration was then selected based on the ability to restore pressure distribution in the knee, manufacturability, and long-term safety. The optimal implant design entailed a PCU meniscus embedded with circumferential reinforcement made of polyethylene fibers. This selected design can be manufactured in various sizes, without risking its integrity under joint loads. Importantly, it produces an optimal pressure distribution, similar in shape and values to that of natural meniscus. We have shown that a fiber-reinforced, free-floating PCU meniscal implant can redistribute joint loads in a similar pattern to natural meniscus, without risking the integrity of the implant materials.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic descriptions of the medial meniscal implant design and evaluation process

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Figure 2

The geometries of the medial meniscus and the (a) femoral and (b) tibial surfaces contacting it were extracted from sagittal MRI scans of a cadaveric male left knee to produce a (c) three-dimensional solid model of the medial knee. The solid model was then exported to (d) a finite element solver where it was loaded with 1200 N. All nodes on the distal surface of the tibia were fixed for all translations and rotations. The outer perimeter of the implant was fixed by a dozen springs (stiffness modulus k=0.05 N/m) connected to the ground.

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Figure 3

The meniscal implant composed of a polycarbonate-urethane (PCU) matrix, reinforced with circumferential polyethylene (PE) fibers

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Figure 4

(a) The setup for the in vitro experiments. The femur and tibia of a normal human cadaveric knee was fixed with bone cement to specially designed holders in a knee compression apparatus. Contact pressures under the intact medial meniscus or the implant were measured using (b) force sensors while subjecting the knee to 1200 N vertical compression.

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Figure 5

(a) Contact pressure maps on the tibial plateau for calculated (left frame) and measured (right frame) configurations; (b) pressures along peripheral paths I (measured) and II (calculated) were plotted

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Figure 6

(a) Calculated contact pressure maps under the selected reinforced meniscus implant loaded from 0 N to 1200 N, (b) corresponding contact pressure maps measured in vitro under an intact natural meniscus loaded from 0 N to 1200 N, (c) calculated contact pressure maps under a nonreinforced meniscus implant loaded from 0 N to 1000 N (due to excessive deformations in this model, the analysis could not be completed up to 1200 N)

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