Age / Sex : 10 / F

Chief complaint: persistent left knee pain and flexion difficulty after trauma (5MA)

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Courtesy: Kyung Sik Ahn, Korea University Anam Hospital

Patellofemoral friction syndrome, Patellar tendon–lateral femoral condyle friction syndrome

Discussion

Findings:

MRI shows focal edema at the inferolateral aspect of the patellofemoral joint (superolateral Hoffa fat pad). Note the high riding patella.

Differential Diagnosis: Hoffa’s disease

Diagnosis: Patellofemoral friction syndrome

Discussion:

Inflammatory changes within Hoffa’s fat pad can be categorized into three main forms according to the location of the inflammation. The most commonly described is Hoffa’s disease (also known as Hoffa’s fat pad impingement) which shows diffuse and widespread abnormalities involving the posterior aspect of the fat pad between the femur and tibia. Another form is infrapatellar plica syndrome, which shows abnormalities along the course of infrapatellar plica in Hoffa’s fat pad. The relationship between Hoffa’s disease and infrapatellar plica syndrome is not clear, therefore, sometimes the two may be difficult to differentiate. A third condition is impingement of the superolateral aspect of the fat pad between the patellar tendon and lateral femoral condyle. This is clinically more common but radiologically more subtle.

MRI can reveal focal area of high T2 signal intensity (edema) at the inferolateral aspect of the patellofemoral joint, within the superolateral portion of Hoffa’s fat pad. Cystic changes may also be seen adjacent to the lateral femoral condyle. Edema in superolateral Hoffa’s fat pad may be an important indicator of underlying patellofemoral maltracking or impingement in younger, symptomatic patients. Reported associated findings include patella alta, lateral patellar subluxation, patellar tendon pathology, and cartilage abnormality.

In evaluating anterior knee symptoms, MR imaging allows identification of changes that may be related to patellofemoral friction syndrome and that should be distinguished from other causes of anterior or lateral knee pain.

References:

Saddik D, McNally EG, Richardson M. MRI of Hoffa’s fat pad. Skeletal Radiol 2004;33(8):433–444.

Chung CB, Skaf A, Roger B, Campos J, Stump X, Resnick D. Patellar tendon-lateral femoral condyle friction syndrome: MR imaging in 42 patients. Skeletal Radiol. 2001;30(12):694-697.