QUADRICEPS / SUPRAPATELLAR FAT PAD IMPINGEMENT SYNDROME:
Dr. Ashutosh Pawale.
A 28-year-old man was referred to an MRI center for intermittent anterior knee pain and mild swelling for 3 months. No history of trauma was given.
A sagittal fat saturation image demonstrates a thickened, edematous suprapatellar fat pad (blue arrow), with posterior bulging margins. Also, reactive marrow edema at the patellar upper pole is noted.
Axial fat saturation image demonstrates a thickened, edematous suprapatellar fat pad (arrow), with posterior bulging margins.
DIAGNOSIS: Quadriceps / suprapatellar fat pad impingement syndrome.
Three normal anterior knee fat pads are present at the knee which separates the joint capsule and synovium; the quadriceps (anterior suprapatellar), the femoral (posterior suprapatellar or supratrochlear), and Hoffa (infrapatellar) fat pads.
The quadriceps fat pad is the normal fat pad between the suprapatellar recess posteriorly and quadriceps tendon anteriorly (which normally has a concave dorsal margin). The term quadriceps fat-pad impingement is supposed to be an inflammatory process within the anterior suprapatellar fat, manifested on MRI as high T2 signal, low T1 signal with convex dorsal margins.
A study by Roth, et al demonstrates Anterior knee pain at physical examination was associated with quadriceps fat pad mass effect (chi(2) = 8.76, p = 0.0031), medial collateral ligament abnormality (chi(2) = 4.83, p = 0.0031), and history of anterior knee pain (chi (2) = 22.76, p < 0.0001). Enlargement of the quadriceps fat pad on MRI has a prevalence of 12% and is significantly associated with intermediate or fluid signal intensity of the quadriceps fat pad and anterior knee pain. However, none of the patients in the study by Roth had a history of direct trauma or overuse. The abnormality thus may have a developmental cause related to the anatomy of the extensor mechanism or may be related to abnormal mechanics (ref: research gate.net).
Other impingements or friction syndromes occurring in relation to an anterior compartment or peripatellar fat pads are 1. Iliotibial band friction syndrome 2. Patellar tendon lateral femoral condyle friction syndrome (PT-LFCFS) 3. Hoffa disease or infrapatellar fat pad impingement syndrome.