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Musculoskeletal Imaging

E3283. Extrasynovial Inflammation and Impingement of the Knee: A Current Review

Desai K1,  Chang K2,  Garza-Gongora R.2 1. Texas A&M Health Science Center, Temple, USA ; 2. Baylor Scott & White Medical Center, Temple, USA

Address correspondence to K. Desai (

Background Information: Knee pain is a common complaint seen in orthopedic as well as primary care clinics, particularly in active individuals. Patella maltracking and accompanied patella alta may lead to anterior extrasynovial impingement syndromes of the knee that may be mismanaged if not appropriately considered by the clinician. The synovial and capsular layers of the anterior knee and juxtaposed fat pads coexist in a complex relationship, making this specific anatomy difficult to evaluate. MRI is the best imaging modality for evaluation of knee anatomy, particularly with respect to the extrasynovial compartments. The purpose of this educational exhibit is to discuss pertinent knee anatomy, common extrasynovial and impingement syndromes, and diagnostic pitfalls.

Educational Goals/Teaching Points: This education exhibit will detail the anatomic components of the knee. We provide an overview of fat pads and their role in protecting the knee and describe the common extrasynovial impingement and inflammation syndromes of the knee. We will evaluate MRI characteristics of the suprapatellar fat pad, patellofemoral fat pad, infrapatellar fat pad (Hoffa disease), and iliotibial band (ITB) impingement syndromes. Lastly, we will discuss pitfalls in diagnosis and management considerations.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: We will review the anatomic and pathophysiologic considerations along with imaging findings of the knee. The anterior compartment has three intracapsular fat pads, divided into infrapatellar and suprapatellar. These include the infrapatellar fat pad (Hoffa fat pad) as well as the anterior (quadriceps) and posterior (prefemoral fat pad) suprapatellar fat pads. Extrasynovial inflammation and impingement syndromes may affect the suprapatellar fat pad and infrapatellar fat pad (Hoffa disease) and be involved in ITB syndrome, adhesive capsulitis, and patellofemoral malalignment. Given the number of syndromes and various etiologic mechanisms, MRI is essential to evaluation and characterization. High-intensity signals on fluid-sensitive MR images are usually seen in the above-mentioned syndromes. Size and morphology of the fat pad should always be considered when evaluating disorders of the knee. Interestingly, fat pads may allow better visualization of synovial abnormalities, as fat pad edema is believed to be an intermediate step in the progression of the inflammatory reaction of the capsule.

Conclusion: This educational exhibit serves to evaluate and characterize cases of extrasynovial inflammation and fat pad disease. It is important for radiologists to be aware of these syndromes in evaluation of knee MRI. Literature review has shown that impingement syndromes and extrasynovial inflammation of the knee have yet to be defined by radiologists using a standard classification system, and as a result, have been under diagnosed. A better understanding of the pathology and anatomy that is involved in these disorders of the knee will serve to create a clearer path to diagnosis and optimize management by clinicians.