Image Interpretation: Hypoechoic fluid collection superficial to the sesamoid complex at the plantar aspect of the first metatarsophalangeal joint, consistent with an adventitial bursitis. The medial and lateral sesamoids are visualized as hyperechoic structures with posterior acoustic shadowing. The flexor hallucis longus (FHL) tendon is identified between the sesamoids with preserved fibrillar architecture and no evidence of discrete tear or tendinopathy. No sesamoid fragmentation is identified to suggest fracture. A Longitudinal view confirms intact FHL tendon, as well as rules out a first metatarsal phalangeal effusion and confirms adventitial bursitis of the subcutaneous tissue on the plantar aspect of the foot.
Teaching Pearl: Adventitial bursitis can be an underrecognized cause of plantar forefoot pain and swelling, especially when the diagnosis may be anchored on osteoarthritis, stress fracture, sesamoiditis, or plantar plate injury. Ultrasound can show a hypoechoic or anechoic bursal collection in the plantar soft tissues overlying a pressure point, often superficial to the sesamoid complex.
A focused ultrasound scan should correlate the bursa with callus, footwear pressure, and point tenderness. Conservative treatment usually emphasizes offloading the area, shoe modification, orthoses, activity adjustment, and modifying gait or training contributors.
References:
1. Chen X, Zhou G, Xue H, Wang R, Bird S, Sun D, Cui L. High-resolution ultrasound of the forefoot and common pathologies. Diagnostics (Basel). 2022;12(7):1541. doi:10.3390/diagnostics12071541
2. Zidani H, Genah I, Lae M, Bousson V, Laredo JD. Adventitious bursitis in the plantar fat pad of forefoot presenting as a tumoral mass. J Radiol Case Rep. 2020;14(2):12-20. doi:10.3941/jrcr.v14i2.3711
3. Albano D, Bonifacini C, Zannoni S, et al. Plantar forefoot pain: ultrasound findings before and after treatment with custom-made foot orthoses. Radiol Med. 2021;126(7):963-970. doi:10.1007/s11547-021-01354-8