Abstract
<title>Abstract</title> <p>A well-defined, corticated, bipartite ossicle embedded within the substance of the plantar fascia at the plantar midfoot is described. The structure was identified as an incidental finding on weight-bearing plain radiographs in an asymptomatic 56-year-old female. Serial imaging spanning five years documented progressive maturation from two faint mineralization foci to a fully formed corticated ossicle, supporting a primary developmental etiology. Digital grayscale pixel intensity analysis confirmed greater radiographic density of the ossicle (mean 45,748 US units) relative to the surrounding plantar fascia (mean 43,953 US units), consistent with organized osseous tissue. Given its mid-plantar location with no adjacent bone of origin, the structure most closely resembles a sesamoid-type ossicle developing within a fibrous structure. The provisional designation Os Danielis (os plantare fasciae midpedis) is proposed. Its intrafascial position may create a focal zone of reduced tensile capacity — a locus minoris resistentiae — analogous to the mechanical vulnerability of the os tibiale externum at the posterior tibial tendon insertion. Clinicians should be aware of Os Danielis in the differential diagnosis of medial plantar midfoot pain.</p>