Presentation
Injured left knee.
Patient Data
Undisplaced peripheral third vertical tear of the medial meniscus from the anterior horn-body junction through the body to the posterior horn, where there is high signal of the posterior root attachment. No lateral meniscal tear.
Deficient anterior cruciate ligament, presumably chronically torn. No edema. 9 mm anterior tibial translation. Posterior cruciate ligament is intact.
Medial and lateral collateral ligaments are intact. Quadriceps and patellar tendons are intact.
No cartilage defect.
Case Discussion
Chronic anterior cruciate ligament (ACL) ruptures can be missed on MRI because recognizing an absent structure is harder than recognizing an abnormal structure, particularly when there is scarring along the expected course of the ACL and lack of edema. ACL deficient knees can lead to chronic instability and subsequent meniscal injuries (medial >>> lateral) after 6 months and chondral lesions after 12 months.