Sonographic characterization of Hoffa's fat pad. A pilot study

Area of Science:

• Musculoskeletal Ultrasound
• Radiology
• Anatomy

Background:

• The Hoffa's fat pad (HFP) is a common source of anterior knee pain.
• Normal sonographic characteristics of the HFP in asymptomatic individuals are not well-defined in existing literature.

Purpose of the Study:

• To describe the sonoanatomical features of the Hoffa's fat pad (HFP) in young, asymptomatic subjects.
• To establish reference values for HFP echostructure, echogenicity, elasticity, and vascularization using ultrasound.

Main Methods:

• Grayscale ultrasound (US) and color Doppler (CD) US were used to examine 72 knees from 36 asymptomatic subjects.
• Sonoelastography assessed adipose tissue elasticity.
• Echogenicity was quantified using pixel intensity, and vascularity was evaluated with CD US.

Main Results:

• The HFP exhibits a distinct two-layered echostructure: a hypoechoic superficial layer with septae and a homogeneously hypoechoic deeper layer.
• The deeper layer demonstrated higher echogenicity (brighter appearance) than the superficial layer.
• Superficial HFP layer elasticity (88.8 kPa) was significantly greater than the deeper layer (75.3 kPa; p < .001).
• Color Doppler detected blood flow in 55.5% of examined HFPs.

Conclusions:

• This study provides a comprehensive sonographic description of the normal Hoffa's fat pad.
• These findings enhance the utility of ultrasound in differentiating normal HFP from pathological conditions.