A dynamic study of the anterior cruciate ligament of the knee using an open MRI

Recent anatomical and radiological studies of the anterior cruciate ligament (ACL) suggest the ACL length and orientation change during knee flexion, and an open MRI sequencing during knee flexion enables a dynamic ACL analysis. This study's goal is to describe a normal ACL using a 1T open MRI and, in particular, variations in length and insertion angles at different degrees of flexion. Twenty-one volunteers with clinically healthy knees received a dynamic MRI with their knees in hyperextension, neutral position, and flexed at 45A degrees and 90A degrees angles. For each position, two radiologists measured the ACL lengths and angles of the proximal insertion between the ACL's anterior edge and the roof of the inter-condylar notch. Additionally, we measured the ACL's and the tibial plateau's distal angle insertion between their anterior edges and then compared these with the nonparametric Wilcoxon test. The ACL had a significant extension between the 90A degrees flexion and all other positions (hyperextension: 31.75 +/- 2.5 mm, neutral position: 32.5 +/- 2.6 mm, 45A degrees: 35.6 +/- 1.6 mm, 90A degrees: 35.6 +/- 1.6 mm). There was also a significant increase of the angle insertion between the proximal 90A degrees flexion and all other positions, as well as between hyperextension and bending to 45A degrees (hyperextension: 2.45A degrees A +/- 3.7A degrees, neutral: 13.4A degrees A +/- 9.7A degrees, 45A degrees: 33 25 +/- 9.3, 90: 51.85A degrees A +/- 9.3A degrees). Additionally, there is a significant increase in the distal angle insertion for all positions (hyperextension: 133.2A degrees A +/- 5.4A degrees, neutral position: 134.95A degrees A +/- 4.4A degrees, 45A degrees: 138.35A degrees A +/- 5.9A degrees, 90A degrees: 149.15A degrees A +/- 8.6A degrees). Our study is the first to exhibit that a dynamic MRI has a significant ACL extension in vivo during bending. This concept opens the way for further studies to improve the diagnosis of traumatic ACL injuries using a dynamic MRI.