Mina Zakhary MD, Presenter: Nothing to Disclose

Thomas Raymond Slattery MD, Abstract Co-Author: Nothing to Disclose

Ran Thein MD, Abstract Co-Author: Nothing to Disclose

Nogah Shabshin MD, Abstract Co-Author: Nothing to Disclose

Mark E. Schweitzer MD, Abstract Co-Author: Nothing to Disclose

Edema in Hoffa’s and quadriceps fat pads have been previously described as sources of pain. The prefemoral fat pad, the third intracapsular fat pad of the knee, has not been systematically evaluated. The purpose of the study is to determine the prevalence, patterns and clinical correlation of prefemoral fat pad edema.

Initially, 11 clinical cases were accumulated and used as a model for a population study. Next, 478 consecutive knee MRI exams were retrospectively reviewed by 2 observers for the presence of prefemoral fat pad edema. The presence, location, pattern and extent of edema, as well as concurrent MRI findings were recorded. Subsequently, patients’ medical records were reviewed for site of pain, history of trauma/surgery, and physical exam findings. The results of the positive cases were compared to the imaging and clinical findings of an age and sex matched control group.

33/478 (6.9%) retrospectively reviewed cases had prefemoral fat pad edema. Of all 44 positive cases, the average lesion volume was 1.10 cm3. Two distinct edema patterns were noted: In group A, 8 cases, there was a superior patellar osteophyte impinging the fat pad, with superior-central pad edema. In group B, 36 cases, edema involved the inferolateral aspect. 64% of group B patients had a history of trauma, compared to only 38% in group A. Conversly, 38% of group A patients had imaging findings of patellar tendon-lateral femoral condyle friction syndrome, versus 19% in group B. Taken as a whole, there was a significantly increased number of ACL tears (p=0.002), patellofemoral compartment osteoarthritis (p=0.043), and patellar tendon-lateral femoral condyle friction syndrome (p=0.039) in the 44 patient study group when compared to the control group.

There are 2 patterns of focal prefemoral fat pad edema: (A) Superior central edema, directly related to a prominent superior patellar osteophyte impinging on the pad; (B) inferolateral edema, with suggested mechanism being a prior sheer injury or impingement. ACL tears, patellar tendon-lateral femoral condyle friction syndrome and patellofemoral osteoarthritis are more frequently observed in patients with prefemoral fat pad edema.

Inferolateral prefemoral pad edema has a high association with lateral patellofemoral friction syndrome and can result from trauma. Superior prefemoral fat edema occurs when impinged by an osteophyte.

Zakhary, M, Slattery, T, Thein, R, Shabshin, N, Schweitzer, M, Prefemoral Fat Pad Edema in the Knee. MRI Findings in 44 Patients Along with Clinical Correlation and Assessment of Prevalence.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12027198.html