Description
A 32-year-old man was referred to a radiology department for intermittent anterior knee pain and swelling for approximately 6 months. The patient denied any history of major trauma, fracture or infection. MRI was performed to diagnose the cause of knee pain. The axial view of MRI revealed increased patellofemoral joint effusion and the sagittal view of T1-weighted, and T2-weighted MRIs showed an oedema, increased intra-articular fluid and thickening of suprapatellar fat pad (figures 1 and 2). Also, oedema of quadriceps fat impingement is visible at both coronal and axial fat sat T2-weighted sections.
Figure 1.
The axial T2 fat sat image demonstrates increased intra-articular fluid.
Figure 2.
The axial T2 fat sat image demonstrates increased signal and thickening (arrow) within fat interposed between the quadriceps tendon and the suprapatellar bursa.
Knee pain is a very common clinical complaint. Generalised pain in the front of knee has many causes. Numerous traumatic and non-traumatic processes may be encountered, many occurring relative to the anterior compartment, including fat-pad impingement syndromes. Three normal anterior knee fat pads are present at the knee which separates joint capsule and synovium; the quadriceps (anterior suprapatellar), the prefemoral (posterior suprapatellar or supratrochelar) and Hoffa (infrapatellar) fat pads.1 2 The quadriceps fat pad is the normal fat pad between the suprapatellar recess posteriorly and quadriceps tendon anteriorly. The term ‘quadriceps fat-pad impingement’ has been used to describe an inflammatory process within the anterior suprapatellar fat, manifested on MRI as high T2 signal, low T1 signal and mass effect on the quadriceps tendon3 (figures 3 and 4).
Figure 3.
Quadriceps fat pad (arrow) is hyperintense on the sagittal T2 fat sat image (A) and hypointense on sagittal T1 image (B).
Figure 4.
The coronal T2 fat sat image demonstrates increased signal within the quadriceps fat pad and mild effusion surrounding (patella=green arrow, quadriceps fat pad=yellow arrow, effusion=red arrow).
Learning points
Several entities with anterior knee pain that involve peripatellar fat may be encountered when evaluating MR of the knee. Of these, one of the most common is quadriceps/suprapatellar fat-pad impingement syndrome which may be related to chronic microtrauma.
The term ‘quadriceps fat-pad impingement’ has been used to describe an inflammatory process within the anterior suprapatellar fat, manifested on MRI as high T2 signal, low T1 signal and mass effect on the quadriceps tendon.
Footnotes
Competing interests: None.
Patient consent: Obtained.
References
- 1.Jacobson JA, Lenchik L, Ruhoy MK, et al. MR imaging of the infrapatellar fat pad of Hoffa. Radiographics 1997;17:675–91. [DOI] [PubMed] [Google Scholar]
- 2.Schweitzer ME, Falk A, Pathria M, et al. MR imaging of the knee: can changes in the intracapsular fat pads be used as a sign of synovial proliferation in the presence of an effusion". AJR 1993;160:823–6. [DOI] [PubMed] [Google Scholar]
- 3.Shabshin N, Schweitzer ME, Morrison WB. Quadriceps fat pad edema significance on magnetic resonance images of the knee. Skeletal Radiol 2006;35:269–74. [DOI] [PubMed] [Google Scholar]