Spontaneous rupture of the flexor digitorum superficialis tendon of the index and middle fingers: "the pen sign".

We report this case of a flexor digitorum superficialis (FDS) tendon rupture of the second and third fingers of the right hand in a 46-year-old patient. This rupture seems to occur under moderate stress. In this precise situation, the diagnosis was confirmed from the MRI data. Treatment was entirely conservative. However, the clinical presentation of the patient appeared quite original and so misleading to us that we reported this case here and developed the term "pen sign" to describe it. Considering this case, in order to reanimate thumb flexion transferring the fourth finger, FDS would appear to be entirely justified because of the lack of consequent difficulties on fine thumb index finger grasping used when holding pens or fine tweezers. It should also lead us in our everyday surgical practice to attempt to systematically repair the two index flexor tendons when they are damaged.