Presentation
Twisting injury to right knee while dancing. History of right knee instability since childhood.
Patient Data
Moderate sized knee joint effusion. Extensive partial thickness articular cartilage loss from the medial patellar facet. There is a shallow trochlea.
Absence of anterior cruciate ligament. Posterior cruciate ligament intact.
Anterior subluxation of tibia relative to distal femur.
Extensive tear of muscle fibers of popliteus muscle.
Tear of the root of the posterior horn of the lateral meniscus. Macerated posterior horn of the medial meniscus and anterior horn is normal. The posterior surface of the medial tibial plateau is steeply downward sloping.
Collateral ligaments are normal.
Case Discussion
This case illustrates the MRI findings associated with the absence of the anterior cruciate ligament (ACL).
Congenital absence of the ACL was first described by Giorgi in 1956 and is an extremely rare condition (0.017 per 1000 live births). It can present unilaterally or bilaterally and involve the ACL and/or PCL.
Informed patient consent for publication has been obtained
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