ACL and Lateral Meniscus old avulsion fractures without marrow edema

Clinical history: 40Y M patient with previous history of knee injury, now presenting with lateral joint pain, ROM restriction, locking and sounds. 

ACL tibial attachment appears avulsed and displaced postero-superiorly. No marrow edema seen in the tibial attachment site or in the fragment. Orange arrows point to the avulsed fragment from the tibial intercondylar region, which appears more rounded and corticated.

 

Attachment site of anterior root of lateral meniscus is seen avulsed from the tibia, and is seen displaced slightly laterally from the anterior intercondylar region. No marrow edema was seen. Meniscal avulsion to produce a bony detachment is unusual. The meniscus usually detaches from the cortical surface of bone and is then called as a 'floating meniscus'. (Differential consideration for this would be a meniscal ossicle. But this is commonly seen in posterior horn of medial meniscus and a donor site would not be present in the tibia).

 

Irregular near full thickness cartilage losses of the central portion of lateral tibio-femoral compartment is noted with subchondral marrow edema of both surfaces. Yellow arrow points to the cartilage loss, green arrow to the marrow edema. These in addition to the tiny tibio-femoral marginal osteophytes, favor the development of secondary osteoarthritis. Lateral meniscal extrusion is also noted in the coronal images. Blue arrow(s) shows absence of marrow edema in the tibial intercondylar region, indicating the avulsions are old ones. A small old Segond fracture is also seen in the lateral proximal tibia. 

Prominent horizontal tear (yellow arrow) of posterior horn of medial meniscus is noted extending into the tibial surface and the posterior free margin. A multiloculated cystic area (green arrows) is noted close to the posterior horn of medial meniscus, seen communicating with the tear (orange arrow), suggesting a parameniscal cyst.

A small T2 hypointense intra-articular loose body is noted posterior to the medial femoral condyle.

 T2 oblique sagittal images showing the bony avulsions, the meniscal tear and the parameniscal tear.