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 is an underrecognized cause of forefoot pain. In older active patients presenting with "overuse" related plantar forefoot pain and swelling, one may anchor prematurely on degenerative joint disease, stress fracture or sesamoiditis as the primary etiology given the location of symptoms. However, prolonged high heel use shifts the mechanical load onto the forefoot and sesamoid complex, forcing chronic pressure and friction that may predispose to adventitial bursitis. Differential diagnoses include osteoarthritis of the first metatarsophalangeal joint, sesamoiditis, sesamoid stress fracture, FHL tendinopathy, and Morton's neuroma due to overlapping clinical features. Point of care ultrasound is an essential imaging modaility for differentiating adventitial bursitis from intra articular and osseous disease. A hypoechoic fluid collection seen superficial to the sesamoid complex with preserved sesamoid cortical integrity and intact FHL fibrillar architecture is the hallmark sonographic finding of adventitial bursitis. Osteoarthritis will show hyperechoic bony irregularity and osteophyte formation at the metatarsophalangeal joint. Sesamoiditis will often appear as cortical irregularity and increased vascularity on Doppler imaging. A sesamoid fracture imaging reveals a discrete cortical disruption with associated hypoechoic edema. Systematic scanning in both transverse and longitudinal planes is important to avoid misattributing superficial bursal pathology to degenerative disease, especially in in older patients.