Medical technology: Mapping the meniscus

The knee joint is a highly complex biomechanical evolutionary achievement. Anyone who has suffered an injury there knows the painful tests of patience during diagnosis and therapy. A non-trivial player in the anatomical orchestra of the compound joint is the meniscus cartilage. Empa researchers are now creating a "3D map" of the precious cartilage.

As a crescent-shaped sliding cushion, the meniscus absorbs shocks and enables smooth movement between the upper and lower leg. However, the two menisci per knee are susceptible to wear and injury. For example, about one in three knees in the population age 40 and older exhibits significant meniscus wear, and about 15 percent of all knee joint accidents involve the meniscus. According to the accident insurance company Suva, these accidents alone cause annual health care costs of over 650 million Swiss francs in Switzerland.

If a surgical procedure is to be performed on the knee, the meniscus is generally not a favorable candidate because the so-called fibrocartilaginous tissue is only supplied with blood in certain sections. Precise knowledge of this valuable vascular plexus is helpful in improving healing chances. Until now, however, information has been based on two-dimensional images of tissue sections. This means that valuable data is lost, for example, on the deformability of the tissue or the interconnectedness of the vessels.

"We want to create a three-dimensional 'map' through the meniscus with high precision," explains Federica Orellana from Empa's Center for X-ray Analytics in Dübendorf. According to the biophysicist, this could optimize treatment and enable tailored therapies in the sense of personalized medicine.

Below the millimeter limit

Federica Orellana and the principal investigator of the project, Annapaola Parrilli, are striving for a level of accuracy that cannot be achieved with equipment in hospitals. Compared to the millimeter resolution of clinical computer tomography, the micro- and nano-computer tomographs in Empa's laboratories can even go below the micrometer limit.

From these radiological images, the researchers create mathematical models that can be used to record and map the density, structure, biomechanical deformability, and vascular network of cartilage in space.

Together with clinical partners at the Istituto Ortopedico Rizzoli in Bologna, the Cantonal Hospital Winterthur, and the University of Zurich, the researchers are currently working with a large number of laboratory samples in order to build up as meaningful a database as possible. Initial computer simulations already show the branching veins in the meniscus with promising precision.

The micro-CT images convey the structural complexity of the meniscal tissue and, in the mathematical modeling, also allow further information such as the porosity or how strongly the blood vessels are tortuous.

Federica Orellana is currently working on a 3D atlas of healthy meniscus tissue samples. In the next step, CT images of all kinds of injuries and wear and tear will be integrated into the models. Patients could thus receive essential information on the self-healing potential of the tissue directly during an examination, and the strategies for individual treatment could be optimized. The biophysicist emphasizes that the 3D map can be used for accident patients as well as for wear and tear processes in old age.

Provided by Swiss Federal Laboratories for Materials Science and Technology