Multipartite hallux sesamoid

Multipartite hallux sesamoids are a commonly seen normal variant, present in up to 33% of hallux sesamoids. They are more commonly bipartite than tripartite. 

The medial (tibial) sesamoid is more likely to be multipartite than the lateral (fibular) sesamoid because it more commonly has more than one ossification center. Bipartite hallux sesamoids are bilateral in ~70% (range 50-85%) of cases. 

Differential diagnosis

The principal differential diagnosis is a hallux sesamoid fracture. It can be difficult to differentiate because bipartite hallux sesamoids are more likely to fracture than complete hallux sesamoids. Features that support a bipartite over a fractured sesamoid include:

• transverse lucency
• smooth, well-corticated margins
• sum of the two parts is greater than the adjacent (and hopefully normal) sesamoid