Normal Suprapatellar Bursa Width on MRI
The suprapatellar bursa is a synovial-lined recess located superior to the patella, deep to the quadriceps tendon, and continuous with the knee joint cavity in most adults. Accurate measurement of its width on MRI is essential for detecting pathological fluid accumulation, which may indicate joint effusion, inflammatory arthritis, or localized bursitis.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | <5 mm |
Clinical Significance
A lateral suprapatellar bursa width of 5 mm or greater is considered abnormal and warrants further clinical correlation. Distension of this bursa most commonly reflects intra-articular pathology, as the suprapatellar recess communicates freely with the knee joint in the majority of the population. Even small increases in fluid volume can be reliably detected on MRI, making it a sensitive indicator of early synovial disease.
Fluid signal within an enlarged suprapatellar bursa should prompt evaluation for underlying causes. Key pitfalls include overcalling a physiologically small amount of fluid as pathological, and failing to recognize complex or intermediate-signal fluid that may represent hemarthrosis, lipohemarthrosis, or purulent material rather than a simple effusion.
- Reactive joint effusion (post-traumatic or post-operative)
- Inflammatory arthropathy (rheumatoid arthritis, crystal arthropathy)
- Septic arthritis or bursitis
- Hemarthrosis or lipohemarthrosis
- Pigmented villonodular synovitis (PVNS)
Reference: Pope TL, M.D. JH. Harris & Harris' The Radiology of Emergency Medicine. Lippincott Williams & Wilkins. (2012).
Imaging Notes
On MRI, the suprapatellar bursa is best evaluated on sagittal sequences, particularly fluid-sensitive sequences such as fat-suppressed proton density or T2-weighted imaging. The bursa width is measured in the lateral plane as the maximum anteroposterior dimension of the fluid-filled recess, superior to the patella and deep to the quadriceps tendon. A small physiological amount of fluid may be present and should not be overcalled.
Axial sequences are useful as a complementary view to assess bursal shape and wall thickening, which may suggest synovitis or infection. Synovial enhancement on post-contrast sequences can help differentiate simple effusion from inflammatory or infectious bursitis when clinical uncertainty exists.