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Abstract Presented at the 26th Annual Meeting of the Arthroscopy Association of North America| Volume 23, ISSUE 6, SUPPLEMENT , e5-e6, June 2007

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Magnetic Resonance Imaging Measurement of the Two Bundles of the Normal Anterior Cruciate Ligament (SS-09)

      Summary

      To date, no study has assessed the magnetic resonance imaging (MRI) appearance of the AM and PL bundle. The purpose of this study was to assess the MRI appearance of the AM and PL bundle in patients with a normal ACL in order to determine the average length and width of each bundle as measured on digital imaging.In the sagittal plane MRIs, the AM bundle was an average of 36.9 mm ± 2.8mm in length, and 5.1 mm ± 0.7mm in width. The PL bundle, by contrast, was an average of 20.5mm ± 2.4mm in length, and 4.4 ± 0.8mm in width. In the coronal plane, the width of the AM bundle was 4.2 ± 0.8mm and the PL bundle 3.7 ± 0.8mm.

      Purpose

      Anatomical studies have shown that the normal anterior cruciate ligament (ACL) consists of two distinct functional bundles, the anteromedial (AM) and posterolateral (PL) bundles. Cadaveric measurements of the bundles have revealed that the AM bundle is approximately 38mm in length and 7.1 mm in diameter, while the PL bundle is 18mm in length and 6.7 mm in diameter.
      Arthroscopic assessment has shown that all individuals with a normal ACL, regardless of age, have both an AM and PL bundle. To date, no study has assessed the MRI appearance of the AM and PL bundle. The purpose of this study was to assess the MRI appearance of the AM and PL bundle in patients with a normal ACL in order to determine the average length and width of each bundle as measured on digital imaging.

      Methods

      Fifty consecutive MRIs of the knee were prospectively collected using a 1.5 Tesla magnet. Demographic data was collected including age, gender, height and weight.
      The length and width of each ACL bundle were measured on digital MRI using Stentor, Philips Medical System. Measurements were performed on sagittal and coronal images through the ACL and were independently measured in blinded fashion by 2 observers. In the sagittal plane, the AM bundle was defined as the oblique fibers inserting at the anterior border of the ACL on the tibia and the proximal aspect of the lateral femoral condyle attachment. The PL bundle was defined as the oblique fibers inserting posteriorly on the tibial insertion, and inferiorly on the lateral femoral condyle. In the coronal plane, the AM bundle was defined as the central of the two bundles; where as the PL bundle was defined as the lateral of the two bundles, from its insertion on the tibia to its origin in the intercondylar notch.

      Results

      The average age of patients included was 33.5 years (range: 15-61) There were 20 females and 30 males. Both the AM and PL bundles were visualized for all 50 patients. In the sagittal plane MRIs, the AM bundle was an average of 36.9 mm ± 2.8mm in length, and 5.1 mm ± 0.7mm in width. The PL bundle, by contrast, was an average of 20.5mm ± 2.4mm in length, and 4.4 ± 0.8mm in width. In the coronal plane, the width of the AM bundle was 4.2 ± 0.8mm and the PL bundle 3.7 ± 0.8mm. The inter-observer reliability for length of the ACL in the sagittal plane was .849 with a 95% CI of .748 to .911 for the AM bundle, and .748 with a 95% CI of .597 to .849 for the PL bundle.

      Conclusion

      This is the first study that quantifies the two anatomic bundles of the ACL based on MRI. Digital MRI allows for a high degree of accuracy. Providing precise measurement of the AM and PL bundles of the ACL on MRI allows for an accurate determination of damage to one or both of the bundles following injury.