Age / Sex : 30 / M

Chief complaint: Anterolateral knee pain

What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Please submit only one answer)

Courtesy: Soo Jeong Yoon, Kangdong Seong-Sim Hospital

Infrapatellar plica

Discussion

Findings: Linear hypointense structure in intercondylar notch lying anterior to ACL continuity with Hoffa's fat pad and inserting into inferior pole of patella (more prominent intercondylar component).

Differential Diagnosis: ACL partial tear

Diagnosis: Infrapatellar plica

Discussion:

The plicae of the knee are normal synovial folds that are remnants from the embryologic development of the knee. At arthroscopy a normal infrapatellar plica has a variable appearance. It is a thin, pliable fold of synovial tissue with elastic and areolar components. The infrapatellar plica may be a complete septum or may be partially attached to the anterior cruciate ligament. The infrapatellar plica may be split, fenestrated, or absent.

Imaging findings

MR; Linear low-signal-intensity structure anterior to and paralleling the ACL on sagittal images.

The IPP continues inferiorly in the knee through Hoffa’s fat pad and loops superiorly to attach to the inferior pole of the patella.

References:

1. Kosarek FJ¹, Helms CA. MR appearance of the infrapatellar plica. AJR Am J Roentgenol. 1999 Feb;172(2):481-4.

2. Cothran RL, McGuire PM, Helms CA et al. MR imaging of infrapatellar plica injury. AJR Am J Roentgenol. 2003 May;180(5):1443-7.