Ligamentum mucosum

Last revised by Dr Magdalena Chmiel-Nowak on 09 Mar 2020

The ligamentum mucosum, also known as the infrapatellar plica, is an embryological remnant of a synovial septum and one of the types of knee plicae

It is the most common knee plica, with incidence ranging from 65% 4 to 85.5% 5 of the population.

The classification according to the plica morphology was proposed by Kim 4.

  • separate type - completely separated from the ACL (60.5%)
  • split type - longitudinally divided (13.5%)
  • vertical septum type - attached to the ACL (10.5%)
  • fenestra type - with fenestrated vertical septum (1.0%)

It is best seen on T2/PD sagittal images as a curvilinear, low signal structure, originating from the anterior intercondylar notch and traversing the infrapatellar (Hoffa's) fat pad to attach to the inferior pole of the patella. It may connect to the anterior cruciate ligament (ACL). Its thickness ranges from very thin to almost as thick as the anterior cruciate ligament.

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Cases and figures

  • Case 1: ligamentum mucosum injury
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  • Case 2: normal
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