Stump entrapment of the anterior cruciate ligament in late childhood and adolescence.

Displacement of a portion of the torn anterior cruciate ligament (ACL) into the intercondylar notch can cause a focal fibrotic reaction similar to that seen following ACL reconstruction. This displacement, which can result in locking or limitation of knee extension, is termed stump entrapment and is described in adult MR imaging literature. We present a pictorial essay of the etiology and appearance of stump entrapment on MR imaging of the knee in an older child and adolescents and review the significance of this finding.