Arthroscopic Untethering of the Fat Pad of the Knee: Release or Resection of the Infrapatellar Plica (Ligamentum Mucosum) and Related Structures for Anterior Knee Pain

Abstract

Anterior knee pain (AKP), a multifactorial symptom complex, can be successfully treated surgically. A specific diagnosis often cannot be made, but the pain is linked to an unrecognized common factor in most patients: the mechanical behavior of the non-isometric contents of the anterior compartment of the knee—the fat pad (FP) and infrapatellar plica (IPP). The objective of this presentation is to describe an effective arthroscopic technique that treats AKP by addressing this common factor. The operation consists of release or resection of the IPP, or ligamentum mucosum, which tethers the FP. These highly innervated tissues act together as a hydraulic shock absorber, filling the anterior compartment. They stretch and deform at the extremes of knee motion because of constraint centrally by the non-isometric IPP. These dynamic changes in shape are eliminated when the plica is released or resected. Pain perception is from perturbed nociceptive nerves: pain relief results from de-tensioning these contained nerves by untethering the fat pad. Ascribing pain causation is problematic because morphologic change, such as inflammation, fibrosis, or contracture of these structures, is only present in a minority of cases. Nonetheless, AKP is both physically linked to these central, pain-sensitive structures and relieved by this operation.

Central patellar portal placement frequently provokes anterior knee compartment radiological abnormalities in anterior cruciate ligament reconstruction

“…There are several studies with findings similar to this study regarding symptomatic infrapatellar fat pad fibrosis. The previous studies reported that anterior interval fibrosis might cause anterior knee pain [28], and that good outcomes can be obtained after the release of anterior scar tissue [20, 25, 27]. Fibrosis of the anterior interval can be caused by trauma to the infrapatellar fat pad via direct injury to the ACL or patellar tendon or by iatrogenic injury due to the creation of arthroscopy portals and post‐ACL reconstruction scarring associated with tendon harvest or fat pad resection [2, 12, 26].…”

Plicae: Where Do They Come from and When Are They Relevant?

“…4,13 Its size can range from a thin band to a broad membrane. 2 Posteriorly, it may be either continuous or separated from the anterior cruciate ligament (ACL), 13,41 and it may even encircle the ACL to divide the inferior aspect of the knee joint into two separate compartments. 2 An insertion to the medial surface of the lateral femoral condyle was also described.…”

“…42 A more horizontal course was also reported. 41 The infrapatellar plica poses some nuisance during arthroscopy. When the plica manifests as a complete septum, it can prevent the arthroscope from being passed between the medial and lateral compartments of the knee.…”

“…43,44 The plica can also impinge on the intercondylar notch and with associated chondromalacia. 41 Fat pad and patellar tethering were also reported. 41,45 In addition, ruptured or partially torn infrapatellar plicae were documented, leading to hemarthrosis.…”

“…41 Fat pad and patellar tethering were also reported. 41,45 In addition, ruptured or partially torn infrapatellar plicae were documented, leading to hemarthrosis. 45 In the past decades when pneumoarthrography was more commonplace, the infrapatellar plica was reportedly misidentified as the ACL.…”