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Tibiofemoral contact and alignment using Upright, Open Magnetic Resonance Imaging (UO-MRI) in patients with Anterior Cruciate Ligament (ACL) rupture Stockton, David John


Problem: Surgery to reconstruct the Anterior Cruciate Ligament (ACL) does not mitigate the elevated risk of arthritis after ACL rupture. There is indirect evidence of persistent contact and alignment changes in the tibiofemoral articulation post-reconstruction, but this has not been quantified with direct measurements in standing, weightbearing positions. Our aims were: 1) to establish the reliability and accuracy of a direct method of determining tibiofemoral contact with Upright, Open Magnetic Resonance Imaging (UO-MRI), 2) to assess differences in knees with ACL rupture treated nonoperatively versus operatively, and 3) to assess differences in knees with ACL rupture versus healthy knees. Methods: Using UO-MRI, we investigated tibiofemoral contact area, contact centroid location, and alignment under standing, weightbearing conditions with knees extended. We assessed the inter-rater, test-retest, and intra-rater reliability in 5 participants with ACL rupture. We assessed accuracy by comparing the contact area of bovine osteochondral blocks axially loaded in a custom jig in the UO-MRI against a high resolution 7T MRI. We then conducted a biomechanical study involving 8 participants with ACL rupture treated nonoperatively and 10 treated operatively, all of whom were high functioning and had returned to sport. We compared contact area, centroid location, and alignment between the operative and nonoperative cohort, and in ACL-ruptured knees versus healthy contralateral control knees. Results: Our methods demonstrated acceptable reliability for contact area and centroid location measurements, with intra-class correlation coefficients of 0.83 to 1.00 in the sagittal plane. Contact area measurement was accurate to within 4.8% measurement error. At a mean 2.7 years after injury, knees with ACL rupture had a 10.4% larger contact areas and a medial contact centroid that was located 5.2% more posterior. The tibiae of knees with ACL rupture were 2.3mm more anterior, and 2.6° less externally rotated relative to the femur, than contralateral control knees. We found no differences between ACL-reconstructed and nonreconstructed knees. Conclusion: ACL rupture was associated with significant mechanical changes 2.7 years out from injury, which ACL reconstruction did not restore. These findings may partially explain the equivalent risk of post-traumatic osteoarthritis in patients treated operatively and nonoperatively after ACL rupture.

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