LAUSR

Objective This study aimed to describe the “fat brook” (FB) in the popliteal fossa of a cadaver and to evaluate its clinical significance. Methods Ten fresh cadaveric knees underwent magnetic resonance imaging and histologic analyses. In addition, magnetic resonance imaging images from 321 patients (108 men, 213 women; mean age, 49.8 years; age range, 5–92 years) were retrospectively reviewed. Two radiologists independently determined the presence/absence of the FB and internal derangement of the knee. Results The FB was present in all cadaveric specimens without synovial lining or joint communication. In the clinical study, the prevalence of FB was 97.8% (314/321). The FB was associated with effusion (P = 0.001) and tear of the medial meniscus (P = 0.022). There was no significant association between prevalence of FB and age or other structures. Determining FB and internal derangement of the knee had excellent interobserver agreement (concordance correlation coefficient = 0.966, 0.834–1.000). Conclusions The FB might be a part of the superficial layer of superficial fascia and not be mistaken for a fat fracture or Morel-Lavallée lesion.