Anterior suprapatellar (quadriceps) fat pad impingement syndrome is a controversial cause of anterior knee pain although anterior suprapatellar fat pad oedema may often, and possibly more commonly, be incidental or considered an anatomical variant ^1,2,11. 

Clinical presentation

Patients present with anterior knee pain and with the point of tenderness at the superior pole of the patella. The pain is exacerbated on deep knee flexion.

Pathology

Aetiology

The aetiology is unclear. It is suggested to result from repeated microtrauma resulting in fibrosis and haemorrhage. There is no significant correlation with patellofemoral maltracking ⁸. There is an association with patellofemoral joint degeneration ⁹.

Radiographic features

MRI

The anterior suprapatellar fat pad is oedematous compared to the prefemoral fat pad, enlarged (≥10 mm AP diameter) with a mass effect on the adjacent suprapatellar recess (i.e. a convex border) and quadriceps tendon ^1-4.  

• T1: low signal within the suprapatellar fat pad

• T2: high signal within the suprapatellar fat pad

• T1 C+ (Gd): enhancement of the suprapatellar fat pad

The most common associated MRI findings are joint effusion and quadriceps tendinitis ¹⁰.

Treatment and prognosis

Initial management is usually conservative, like anti-inflammatory medications and decreased painful activities. Complete pain resolution can be achieved with ultrasound-guided injection of anaesthetic or corticosteroid followed by physical therapy ⁶. Surgery could be considered in cases with persistent symptoms by laparoscopic resection ⁷.

Differential diagnosis

In the absence of anterior knee pain, quadriceps fat pad oedema diagnosis cannot be made based solely on MRI findings ^1,2.