The MR appearance of the infrapatellar plica

OBJECTIVE. Our purpose is to describe the MR appearance and clinical releva nce of the infrapatellar plica of the knee and to assess possible imaging p itfalls resulting from lack of recognition of this normal structure. Seven patients-four from our institution and three from our teaching file from ou tside institutions-were selected because they displayed the imaging feature s of the infrapatellar plica. CONCLUSION. The infrapatellar plica is readily appreciated on sagittal MR i mages of the knee as a low-signal-intensity structure in the intercondylar notch just anterior to the anterior cruciate ligament (ACL). The infrapatel lar plica is important to recognize for the following reasons: It may be co nfused with an intact ACL because of its proximity and similar signal chara cteristics; it may pose difficulty to the arthroscopist when attempting to move instruments from the medial to lateral compartments of the knee; it ca n block clear visualization of the ACL during arthroscopy; and it can impai r retrieval of loose bodies in the intercondylar notch. Familiarity with th e infrapatellar plica should allow one to differentiate this normal structu re from other structures in the knee and aid in preoperative planning.