"Fat Brook" in the Popliteal Fossa: Cadaveric and Clinical Investigation With Magnetic Resonance Imaging.

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.