Blumensaat's line

Written by Dr Sheila Strover on March 14, 2025

Blumensaat's line is a linear shadow on lateral X-rays of the knee that corresponds to the roof of the intercondylar notch that houses the cruciate ligaments between the two rounded condyles of the femur.

On this lateral X-ray the red line marks what is referred to as Blumensaat's line.

Lateral X-ray to show the position of Blumensaat's line.

Blumensaat's line in cruciate ligament surgery

During cruciate ligament reconstruction, the surgeon - by referring to Blumensaat's line - can get an idea of how long to make the new graft construct.

Illustration of the knee joint from the front (knee bent) to show the roof of the notch.
Looking into the joint from the front, one can clearly see the roof of the notch, and the anterior cruciate ligament reaching across the joint.
Lateral X-ray of the knee to show how the Blumensaat's line is easy to visualise as long as the two condyles overlap one another.
The lateral X-ray (looking from the side) allows the two condyles to be lined up, which then clearly identifies with a shadow where the roof of the notch lies, and how long the replacement graft should be.

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Blumensaat's line in patella alta

Blumensaat's line is also useful in the diagnosis of patella alta, or 'high-riding' patella.

Extending the line to beyond the X-ray shadow of the patella (kneecap) gives an indication of whether or not the patella is abnormally high or low, as it would normally intersect the lower pole of the patella.

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Tibial tunnel, Condyle, Intercondylar notch, Anterior cruciate ligament reconstruction, Patella alta, Caton-Deschamps index, Cruciate ligament, Patella alta, Patella infera, Patella baja

Contributions by experts -

Dr Ronal P Grelsamer - Imaging and X-rays for patellofemoral pain (part of a Course on Patellofemoral Pain)

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