Anterior cruciate ligament tear. A new diagnostic index on magnetic resonance imaging

An objective index of anterior cruciate ligament (ACL) tears based on posterior cruciate ligament (PCL) shape has been introduced. The PCL shapes on magnetic resonance imaging (MRI) were measured in 67 patients (31 normal ACL, 31 torn ACL, and five partial ACL tears, all confirmed by arthroscopy). All of the measurements were performed in a blinded manner, without previous knowledge of the MRI or arthroscopy diagnosis. The index consisted of the ratio B/A, with B equaling the length of the line between the posterior inferior tibial and the superior anterior femoral attachment of the PCL, and A equaling the maximum perpendicular distance from this line to the PCL. All measurements were performed twice, and the mean was used for statistical significance. The average index ratio was 5.4 and 3.9 for normal ACL and torn ACL, respectively. Using a cutoff value of 4.75, the sensitivity of the index was 87% and the specificity was 84%. An objective and reproducible index measurement of PCL shape for normal and injured ACL has been established. It provides additional information for both orthopaedic surgeons and radiologists in the diagnosis of ACL injury.