Magnetic Resonance Signal Abnormalities Within the Pericruciate Fat Pad: A Possible Secondary Sign for Acute Anterior Cruciate Ligament Tears

Purpose The study sought to investigate the presence of magnetic resonance (MR) signal alterations within the pericruciate fat pad in patients with an acute anterior cruciate ligament (ACL) tear as well as evaluate its diagnostic value in comparison with the main secondary signs of ACL tears. Methods Two musculoskeletal radiologists retrospectively reviewed knee MR examinations performed from May to October 2015. The ACL was considered as torn or intact based on either previous arthroscopic findings or unequivocal MR imaging interpretation if arthroscopic correlation was unavailable. Abnormalities of the pericruciate fat pad were evaluated as increased signal on the fluid-sensitive sequences; the main secondary signs of ACL tears were identified. Sensitivity and specificity were calculated for each sign. Results A total of 182 patients entered this study: 22 with an acute ACL tear, 160 with intact ACL. Signal hyperintensity of the pericruciate fat pad was demonstrated in all patients with an acutely torn ACL, resulting significantly different between individuals with intact ACL and those with ligament tear (P <.0001). This sign was much more sensitive (100%) but less specific (72.5%-75%) than other secondary signs. Conclusions Signal hyperintensity of the pericruciate fat pad on the fluid-sensitive sequences is associated with acute ACL tears and could be considered as a possible indicator of these injuries.