Last updated on 9th of May 2025
Description
The TT-TG index (Tibial Tubercle-Trochlear Groove Index) is a radiological measurement used to evaluate the lateral displacement of the kneecap (patella) in relation to the thigh bone (femur). This measurement is often performed on patients with patellar luxation or other kneecap problems.
This procedure is only available in the Axial orientation for CT or MRI. However, a knee representation is required.
Measurements
The measurements made by the procedure are displayed in the image:
- TT-TG distance: is the distance between TT and TG lines.
Auxiliary references
- Posterior condylar line (PCL): is the line drawn between the medial femoral condyle and
the lateral femoral condyle. - Tibial tubercle (TT): a perpendicular line drawn from the PCL to the highest point of the tibial tuberosity.
- Trochlear Line (TG): a perpendicular line drawn from the PCL to the lowest femoral trochlear groove.
How to perform
After selecting this procedure in the sidebar, you must mark the points to conclude it. To see the caption of each point you need to click on this button 
Note: You can change the position of the points at this stage or later. To do this, simply click on each handle with the left mouse button and move them to the most suitable position.
This procedure has no advanced configuration.