In the frame of the EU project RESTORE, Reykjavik University is developing the 1st European database of chondral lesions’ morphometric and associated 3D models by gathering and processing CT and MRI data from patients suffering from degenerative and traumatic cartilage. This work will serve as a benchmark for bioprinting of synthetic cartilage and for understanding the quantitative and qualitative factors associated with individual patients.

The database consists of 24 degenerative (D) cartilage, 15 traumatic (T) and 8 healthy controls (C). The database of chondral lesions will contain several types of information, including results about cartilage density. The density extracted from the datasets is measured in Hounsfield Unit (HU). The Hounsfield scale is a quantitative scale used for describing radiodensity. The radiodensity of water is 0 HU, and the air is -1000 HU, fat ~-100 HU, muscle 100 HU, a bone from 100-200 to 2000+ HU. The cartilage has been segmented from MRI images and the bone from the CT images. After that, the two datasets are combined through the image registration process. Then, the average cartilage density for each part of the knee (femur, tibia, and patella) has been extracted for each patient. This value can be averaged for each patient category (degenerative, traumatic, control) to study cartilage density behaviour and quality. The density values are displayed in Figure 1 for the femoral cartilage, patellar cartilage, medial tibia cartilage, and lateral tibia cartilage.

Figure 1. Cartilage density for each part of the knee (femur, tibia, and patella) in Hounsfield units (HU) for different patient groups (degenerative D, traumatic T, and healthy controls C).

This preliminary analysis shows that the degenerative cartilage has the highest density for all parts, whereas the control cartilage has the lowest. It has to be known that the knee cartilage contains water fluid, which has a density of around 0 HU. When the cartilage is ageing or starts to degenerate due to different conditions, such as osteoarthritis, it calcifies little, leading to the disappearance of the water. Therefore, the radiodensity of the cartilage becomes higher. It explains that the D group is showing the highest density for every cartilage, whereas the C group has the lowest. The T group comprises people suffering from an accident that did not necessarily impact the same part for every subject. Moreover, the age range of this group is younger than for the D group. That is why we can assume that the cartilage has a lower density than the D group and behaviour closer to the C group.