This 17-year-old male reports with knee pain following a foo | Figure 1

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This 17-year-old male reports with knee pain following a football injury. Be sure to size up the case by looking at the first two images without arrows before looking at the same images with arrows to indicate key findings.

What are the anatomical structures indicated by the arrows? (Note: Arrows will be provided with the follow-up) Hint: While this patient's anterior cruciate ligament (ACL) is intact, these structures are very important in the setting of acute ACL tear. #KneeMRI #MRI #Radiology #RadRes

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Cases


Sagittal FS T2-weighted MRI and lateral radiograph (prior post) show a displaced fracture of the tibial spine/intercondylar eminence (black arrows) with a large joint effusion (white arrows). The tibial fragment has been avulsed by the ACL (orange arrow), which is intact. Note the open growth plates of the femur and tibia. As opposed to the classic midsubstance ACL tears seen in older children/adults, this pattern of ACL injury is more frequently found in skeletally immature patients.


2 back to back patients. Image 1 shows intact ACL (orange arrow). Image 2 shows disarray of ACL with essentially full thickness tear.


A1 - Image 7 demonstrates an acute ACL tear (blue arrow). In addition, osseous contusions are identified in the posterior aspect of the lateral compartment in both the lateral femoral condyle (red arrow) and lateral tibial plateau (yellow arrow). Image 8 (arrow) also demonstrates an osseous contusion in the anterior medial tibial plateau (anterior medial tibial rim sign). A2 - The rim sign is associated with a significant increased risk of contusions and fractures as well as posterolateral corner injuries and tears of the posterior horn lateral meniscus.


Sagittal T2 weighted MR of the knee in an adolescent shows disruption of the anterior cruciate ligament (arrow). ACL injuries typically occur when an athlete pivots and a valgus stress is applied to the knee in flexion. ACL injuries are more common in boys when the physis is not completely closed (as in this case).

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