Coexistence of two accessory flexor pollicis longus heads or coexistence of two-headed flexor pollicis longus with an unrecognized anatomical structure?

The flexor pollicis longus (FPL) is located in the anterior compartment of the forearm. It is morphologically variable in both point of origin and insertion. An additional head of the FPL can lead to anterior interosseous syndrome. This report presents a morphological variation of the FPL (additional head in proximal attachment and bifurcated tendinous insertion in distal attachment) and an unrecognized structure that has not so far been described in the literature. This structure originates in six heads (attached to the FPL or interosseous membrane) that merge together, and inserts on to the FPL. All the variations noted have clinical significance, ranging from potential nerve compression to prevention of tendon rupture.