Extension Block from ACL Tear

Patients with acute ACL tears can sometimes present with missing terminal extension (inability to fully straighten the knee). One must always suspect a bucket-handle meniscus tear in this situation, but sometimes it is due to “stump entrapment” where a portion of the torn ACL flips forward and gets pinched between the femur and tibia, acting as a mechanical obstruction that limits full extension of the knee.

1️⃣ + 2️⃣ Arthroscopy views of the ACL fragment caught in the intercondylar notch.
3️⃣ + 4️⃣ Sagittal and coronal MRI views of the ACL fragment flipped forward.