Ultrasound evaluation of infrapatellar fat pad impingement: An exploratory prospective study

We sought to determine whether there are ultrasound parameters that differ between knees with symptomatic fat pad synovial impingement and asymptomatic knees.

A prospective study was performed in patients with clinical signs and symptoms of fat pad synovial impingement and asymptomatic controls. Eleven symptomatic knees and 10 asymptomatic controls were evaluated. Ultrasound imaging was performed before and after exercise. Evaluated parameters included largest fat lobule compressibility, subjective assessment of vascularity, largest vessel diameter, and subjective assessment of dynamic fat pad motion during flexion and extension. Receiver operating characteristic (ROC) curve analysis was used to assess whether changes in these parameters were different between symptomatic and asymptomatic knees.

Change in the largest vessel diameter was greater and trended toward dilation in asymptomatic knees compared to symptomatic knees (mean: 0.83 vs. -0.02; P<0.001). No significant differences were observed between symptomatic and asymptomatic knees with respect to pre-exercise versus post-exercise states in subjective assessment of vascularity (P=0.131), fat pad motion (P=0.115), or percent change of the largest fat lobule (P=0.241). However, overall compressibility of the fat pad lobule was significantly diminished in the pre-exercise state in symptomatic knees compared to asymptomatic controls.

This study demonstrated a statistically significant change in the largest vessel diameter from pre- to post-exercise states between symptomatic and asymptomatic knees, as well as abnormal pre-exercise fat lobule compressibility in symptomatic knees. These findings show promise that with further research, ultrasound could have clinical utility in diagnosing infrapatellar fat pad impingement.