Flexor tendon rupture associated with an anomalous muscle.

A rupture occurred in the substance of an apparently normal flexor digitorum profundus tendon of a left small finger. It was associated with a previously undescribed anomalous flexor digitorum superficialis of the brevis type to the same finger. Clinical reports of 20 anomalous flexor digitorum superficialis muscles were found in the literature; all but one were on the right side or bilateral and occurred predominantly in females. Three cases were of the brevis type and all involved the index finger. Although the precise reason for rupture is not known we have speculated that the anomalous superficialis may have given rise to a deficient vinculum longus to the profundus predisposing it to failure.