Blumensaat's line is a linear shadow on lateral X-rays of the knee that corresponds to the roof of the intercondylar notch between the two rounded condyles of the femur.
Page updated May 2024 by Dr Sheila Strover (Clinical Editor)
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.
The lateral X-ray 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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Quote from peer-reviewed paper:
"....The Blumensaat line....will accurately approximate the native ACL....length and may aid in the prevention of [graft tunnel mismatch]...."
Citation: Joyner PW, Mills FB 4th, Brotherton S, Bruce J, Roth T, Hess R, Wilcox CL, Leddon CE, Davis B, O'Grady C, Andrews JR, Roth CA. Blumensaat Line as a Prediction of Native Anterior Cruciate Ligament Length. Orthop J Sports Med. 2020 Aug 6;8(8):2325967120943185. doi: 10.1177/2325967120943185. PMID: 32821762; PMCID: PMC7412920.
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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Quote from peer-reviewed paper:
"....Blumensaats line should extend to the inferior pole of the patella at 30 degrees of knee flexion...."
Citation: Wolfe S, Varacallo M, Thomas JD, et al. Patellar Instability. [Updated 2023 Sep 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482427/