Research Papers

Design of Reverse Materials Resurfacing Implants for Mild–Moderate Medial Osteoarthritis of the Knee

[+] Author and Article Information
Hao Yang Chan, Aaron Lerner, Miriam Chaudhary, Joseph A. Bosco

Laboratory for Orthopaedic Implant Design,
Department of Orthopaedic Surgery,
New York University—Hospital for
Joint Diseases,
New York, NY 10003

Peter S. Walker

Laboratory for Orthopaedic Implant Design,
Department of Orthopaedic Surgery,
New York University—Hospital for
Joint Diseases,
301 East 17th Street,
Suite 1500,
New York, NY 10003
e-mail: Peter.Walker@nyumc.org

1Corresponding author.

Manuscript received February 17, 2016; final manuscript received October 17, 2016; published online December 21, 2016. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 11(1), 011004 (Dec 21, 2016) (7 pages) Paper No: MED-16-1038; doi: 10.1115/1.4035083 History: Received February 17, 2016; Revised October 17, 2016

The areas of the most frequent cartilage loss in mild–moderate medial osteoarthritis (OA) were reviewed from previous studies. Implant components were designed to resurface these areas. The surface geometries of the components were based on an average femur and tibia produced from 20 magnetic resonance imaging (MRI) models of normal knees. Accuracy of fit of the components was determined on these 20 individual knees. The femoral surface was toroidal, covering a band on the distal end of the femur, angled inward anteriorly. For a five-size system, the average deviations between the implant surfaces and the intact cartilage surfaces of 20 femurs were only 0.3 mm. For the tibia, the deviations were 0.5–0.7 mm, but the errors were mainly around the tibial spine, with smaller deviations in the central bearing region. Hence, these small implant components would accurately restore the original bearing surfaces and allow for preservation of all the knee structures. Using a thin metal component for the tibia would preserve the strong cancellous bone near the surface, an advantage for fixation. In this case, the femoral component would have a plastic bearing surface, but still be less than 10 mm thickness. Such a design could have a useful place in the early treatment of medial OA of the knee.

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Fig. 1

Typical areas of cartilage loss in medial osteoarthritis: a central band on the distal end of the femur and most of the tibial plateau but excluding the posterior region [5]. The figure is a cartilage thickness model produced from MRI.

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Fig. 2

A plane positioned 2 mm below the lowest bone point and angled to remove the least volume of bone from the medial tibial plateau. The plane was used to assess medial bone subsidence between normal and arthritic tibias.

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Fig. 3

The average medial femoral condyle showing radii in the frontal and sagittal views. In the frontal view, radii were fitted with the femur rotated at flexion angles between 28 deg extension and 42 deg flexion.

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Fig. 4

The surface contours in the frontal and sagittal planes of the medial tibial plateau used to define the geometry of the component. The component is shown with preservation of 3 mm rim of bone and cartilage at the posterior and medial. The resection level at 2–4 deg varus is shown (right).

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Fig. 5

Groups of 20 normal femoral and tibial models were superimposed, and geomagic software was used to produce the average femoral and tibial shapes

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Fig. 6

Contour plots of the bone surface of the average normal, mild OA, and moderate OA used to show medial subsidence. The contours on the femur are relative to a plane over the distal condyles: for the tibia, a plane over the lateral plateau. There are minimal differences in the femurs, but increased varus on the medial side of the tibial plateau for moderate OA, indicating subsidence.

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Fig. 7

Deviation maps between different average femurs and tibias; average normal compared with mild OA cartilage surface, average normal compared with moderate OA bone surface, and male versus female moderate OA bone surfaces

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Fig. 8

The average femur with the circular axis and central plane. A toroid (red) which was angled 8 deg to the central plane was based on the frontal and sagittal radii. The component periphery (yellow) is on the surface of the toroid.

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Fig. 9

A typical example of fit between the femoral component and the femur. The deviations between the implant and cartilage could either be positive or negative.

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Fig. 10

A typical example of fit between the tibial component and the tibia. The goal was to match the tibial surface overall.




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