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The Blumensaat Line on Radiograph as an Accurate Predictor of Native ACL Length

The Blumensaat Line on Radiograph as an Accurate Predictor of Native ACL Length

Jeffrey Simpson, BS, UNITED STATES Joshua Cassinat, BS, UNITED STATES Frederic Baker Mills, MD, UNITED STATES Patrick Wakefield Joyner, MD, MS, UNITED STATES

UCF College of Medicine, Orlando, FL, UNITED STATES

2023 Congress   ePoster Presentation   2023 Congress   Not yet rated


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Summary: Pre-operative measurement of the Blumensaat line on radiograph provides surgeons with a convenient and accurate method for predicting the length of the native ACL.


Accurate graft length is crucial to the success of an anterior cruciate ligament (ACL) reconstruction. Inaccurate graft length can lead to graft-tunnel mismatch (GTM) if the graft is too long or too short. Accurate predictions of native ACL length, therefore, are crucial to avoid complications. The Blumensaat Line (BL) is a radiographic landmark representing the roof of the intercondylar fossa. This study examines if radiographic measurements of the BL are accurate predictors of native ACL length and if they can be consistently measured. 


Radiographs and MRIs were collected in a retrospective analysis of 200 patients with non-ACL knee injuries. Ages ranged from 10 to 89 years. Images were reviewed by three physicians of varying experience levels. The BL was measured on lateral radiograph and native ACL length was measured from sagittal MRI. Measurements were assessed for interobserver reliability. Two physicians measured the BL on radiograph and the ACL on MRI twice each in 50 patients to assess intraobserver reliability for both methods. Pearson correlation coefficients were calculated to test for pairwise associations between ACL on MRI and the BL on radiograph. Linear regression models were created to predict ACL length according to the BL on radiograph.


Interobserver reliability was 0.86 for the BL on radiograph, and 0.71 for the ACL on MRI. Intraobserver coefficients were 0.94 for radiograph and 0.87 for MRI. Pearson’s correlations found a statistically significant correlation between the BL and ACL on MRI for all reviewers. (p < 0.0001). There was a significant linear regression model when comparing the BL to ACL measured on MRI (p < .00001). 

Discussion/Conclusion: These results display a significant correlation between the Blumensaat line on radiograph and ACL as measured on MRI. Measurements of the BL were consistent between multiple physicians and consistently measurable by an individual physician. This accurate consistency shows that measuring the BL on radiograph is a convenient, inexpensive, and reliable method for predicting native ACL length. Use of the BL in preoperative planning should therefore improve graft accuracy and minimize GTM.

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