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

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.