A) Cobblestoning of the anterior knee
B) Heterogeneous appearance of patellar tendon
C) Large joint effusion
D) Hypoechoic fluid collection anterior to patella
Image 1: Illustration of prepatellar bursitis (courtesy of orthoinfo.aaos.org)
Image 2: Clinical example of prepatellar bursa (courtesy of wikipedia.org)
Image 4: Ultrasound of the patella (at the bottom in white) with layered soft tissue edema, a small fluid collection (in black) and some cobblestoning near the surface. Most consistent with septic prepatallar bursitis.
Answer is D. The described patient is most likely to have prepatellar bursitis. Most cases are aseptic and will show a large hypoechoic fluid collection anterior to the patella. In septic cases, there may be cobblestoning but he has no fever or erythema. A joint effusion is unlikely in this vignette given his range of motion is intact. A heterogenous patellar tendon could be possible in the case of patellar tendonitis but doesnt fit the case in question.
- Ho G, Tice AD, Kaplan SR (1978) Septic bursitis in the prepatellar and olecranon bursae: an analysis of 25 cases. Ann Intern Med 89(1):21–27
- Diering, Nina, et al. “Calcific prepatellar bursitis in a patient with limited cutaneous systemic sclerosis.” JDDG: Journal der Deutschen Dermatologischen Gesellschaft 15.12 (2017): 1248-1250.
- Draghi F, Corti R, Urciuoli L, Alessandrino F, Rotondo A. Knee bursitis: a sonographic evaluation. (2015) Journal of ultrasound. 18 (3): 251-7. doi:10.1007/s40477-015-0168-z – Pubmed