Quadriceps fat pad syndrome

Clinical History

33-year-old male patient who had a one year history of recurrent anterior knee pain, more severe on prolonged sitting. No history of recent trauma.

Imaging Findings

PD fat-suppressed sagittal MR images of the knee show extensive quadriceps fat pad oedema with intact extensor mechanism. The rest of the knee joint was normal without evidence of bone, ligament or meniscal injury or pathology.

Discussion

Anterior knee pain, the most common knee complaint, may be caused by a variety of abnormalities that include cartilage disease, patellar instability/dislocation, femoral trochlear dysplasia, tendinopathies, bursal conditions, mediopatellar plica syndrome and Hoffa’s disease. It is not difficult to diagnose these on MRI, although less common aetiologies may be overlooked in spite of the patient’s significant complaints [1-5].

There are three normal fat pads located about the anterior knee: quadriceps (anterior suprapatellar), prefemoral (posterior suprapatellar), and Hoffa (infrapatellar) fat pads. Each is interposed between the joint capsule externally and the synovium-lined joint cavity, making it intracapsular but extrasynovial [6]. Previous studies have demonstrated abnormal MR appearance of these fat pads in relation to symptomatic knees without evidence of internal derangement [4, 6-8].

A normal quadriceps fat pad lies on the patellar base and is triangular, filling the gap between the posterior aspect of the quadriceps tendon insertion and the superior aspect of the retropatellar cartilage to increase the congruency of the extensor mechanism [7, 8]. Focal inflammation involving the anterior suprapatellar fat has been described, manifested on MRI as low T1/high T2 signal with accompanying mass effect on the quadriceps tendon and suprapatellar recesses [8]. Additionally, some have described its imaging appearance as resembling that of Hoffa disease but in a different location [6, 7]. Proposed aetiologies include developmental changes in the anatomy of the extensor mechanism, abnormal mechanics [8], chronic microtrauma or overuse injury [6]. Although some authors favour the overuse mechanism based on its imaging similarities to Hoffa disease, young male predominance, lack of significant association with patellofemoral malalignment or osteoarthritis and symptomatic involvement in highly active patients [6], other more recent investigations have theorized that fat pad oedema may be an early manifestation of an inflammatory process such as rheumatoid arthritis [9, 10].

Because the exact cause of quadriceps fat pad enlargement associated with anterior knee pain at physical examination is not known, a treatment for this problem is also not known. Roth et al. used conservative measures such as physical therapy and intraarticular corticosteroid injection with eventual symptomatic improvement [8]. No surgical management has been reported in existing literature.

Quadriceps fat pad syndrome is a diagnosis of exclusion which must be considered in a highly active patient with persistent anterior knee pain and without evidence of trauma or internal joint derangement. Alternatively, it may also herald the presence of a more systemic inflammatory process such as rheumatoid arthritis.

Differential Diagnosis List

Final Diagnosis

Quadriceps fat pad syndrome

URL:	https://eurorad.org/case/13763
DOI:	10.1594/EURORAD/CASE.13763
ISSN:	1563-4086